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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) .
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why is the smooth endoplasmic reticulum , not involved in protein synthesis ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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why does the mitochondria have its own dna ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm .
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why did you not use the term nuclear membrane ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production .
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do dna have a specific temperature and/or ph to maintain inorder for it to be in a good condition ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it .
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how do organelles get through the outer and inner membrane of the nucleus ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) .
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how are platelets able to function without a nucleus and why do they not have organelles ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum .
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what would happen if a cell not specialized for detoxification , like a muscle cell , had a significantly larger amount of ser ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it .
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why are ribosomes organelles if they do n't have a membrane ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info .
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what happens to cells with damaged dna ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it .
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what percentage of the cell is taken up by cytoplasm ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material .
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where do the substances go after being broken down in a lysosome ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement .
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how do microtubules make the cell move ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament .
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what is the mitotic spindle , and what are its functions ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function .
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are there any cells visible to the naked eye ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory .
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how are ribosomes assembled in the nucleolus ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm .
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nucleus how do the nuclear pores know when to allow proteins and other particles into the cells ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability .
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cytoskeleton what happens when a part of the cytoskeleton gets disconnected ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers .
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does the cytosol destroy the proteins that is it sent by the golgi apparatus or are they just sent back for relabeling ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers .
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how does the golgi apparatus send the proteins to the different paths ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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in the 15th paragraph , were does the mitochondria stores its dna and what process does it have to go through to reproduce ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum .
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in the 8th paragraph , how does a cell decide if it has a smooth or rough er ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it .
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about how many lysosomes are in a single cell ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability .
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how many would have to burst in order for the cytoplasm to be acidic enough for the enzymes to function within the cytoplasm ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability .
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how does a cytoskeleton contribute to movement ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle .
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is the only purpose of the nucleus to house the dna and nucleolus ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material .
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if a lysosome were to break down a non-functioning protein , then would n't at least one of the new amino acids be non-functioning ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside .
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how come the outer membrane 's lipid bilayer of the mitochondria allows small molecules to pass through but the inner membrane 's lipid bilayer is non-permeable ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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how are mitochondria able to have their own set of dna and still be an organelle ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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why does glycolisis occur in the cytoplasm and not in the mitochondria ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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why do mitochondria need or even have 2 membranes ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) .
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what occurs in the perinuclear space ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory .
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how fast is the production of ribosomes in the nucleolus ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) .
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why are the smooth endoplasmic reticulum and rough endoplasmic reticulum not considered completely different organelles and have different names if they have different appearances and functions ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it .
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how does the cell move around ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart .
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not in the sense of flagella and cilia , but rather how it functions at all , without being made of more living cells ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart .
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how does the cell move its cilia and/or flagella in order to propel itself around its environment ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) .
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can organelles live on their own for any amount of time ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells .
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if one organelle stops working correctly , does it immeadiatly effect the rest of the cell , and will it effect cells around it ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes .
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if the prokaryotic cells do n't have membrane bound organelles , then how do they stay in place to form cells ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments .
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how do scientists know the chemical components in a structure as small as an organelle ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made .
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for example how do scientists know that cytoplasm is made up of mostly water and some other materials ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found .
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cytoplasm and nucleoplasm are similar , but what is the key difference other than the fact that they 're found in different locations ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome .
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is one more viscous than the other ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) .
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is the perinuclear space 's only function to separate the nucleus from the cytoplasm ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers .
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how does the golgi apparatus decide which proteins go on each of the four paths ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material .
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the article states that cells can produce proteins and lipids , but can they produce anything else ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) .
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how cells are self-regulating ; relating to major organelles ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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why is mitochondria classified as an organelle if it has its own dna ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum .
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what happens if a cell 's organelle is defective in some way and can not preform its function ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism .
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how are prokaryotes supported if they have no nucleus that controls the cell ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin .
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what 's the major difference between microtubules and microfilaments ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space .
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what would happen to the process of cellular respiration in the mitochondria if the intermembrane space was not a low ph and was more neutral or barely even acidic ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) .
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why does the nuclear envelope have so many layers to separate it from the cytoplasm in the space called the perinuclear space ( it is unlike the other organelles with only two layers and not four ) ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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what diseases in particular come from mitochondria dna defects ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself .
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1 ) how do the ribosomes attach to the exterior of the rough er ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself .
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2 ) what is the difference between the rough and smooth er other than that the rough er has ribosomes on its exterior ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it .
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how does the cytoskeleton move the cell , does it move the organelles or the cell as a whole ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function .
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how do peroxisomes keep ros from hurting our cells , and how do antioxidants play into the picture ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) .
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does that imply that the separate dna of the mitochondria split as well ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory .
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if prokaryotic cells do n't have membrane bound organelles how do they properly function ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum .
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will a cell properly function if it 's dna is n't protected by 2 phospholipid bilayers ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism .
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why would a cell not have a nucleus ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins .
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what modifications does rna have to have in order to leave the nucleus ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) .
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why are n't the rough and smooth endoplasmic reticulum connected ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum .
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is there a specific name for the function of transporting things throughout the cell ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material .
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does the waste that gets put into the lysosome stay in the cell ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it .
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what is the purpose for an inter membrane space ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed .
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what would happen to an enzyme if it were in an environment less acidic than a ph of 5 ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function .
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my question is : do you think fat cells contains more ribosomes than the liver cells ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed .
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what exactly do platelets do ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info .
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why do mitochondria have a set of dna if the nucleus is the organelle meant for storing dna ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) .
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what is the structure of cell organelles ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) .
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what is the structure of cell organelles ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) .
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if the mitochondria is self replicating , then does it just continue to make more of itself in a cell until there is no more room for it ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells .
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in the chart , under `` what 's found inside the cell '' , it says that the functions of peroxisomes is security and waste removal and the function of lysosomes is security and recycling , but what is the differnece between them ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do .
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are there any other differences between eukaryotic and prokaryotic cells ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) .
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are there any other reasons why ribosomes attach to the rough and smooth endoplasmic reticulums ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi .
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what diseases can be traced back to malformation ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers .
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why were the cytosol ever sent to the golgi apparatus ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do .
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what is the main difference between a microtubule and microfilament ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself .
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why does the rough er have ribosomes yet the soft er does not ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it .
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how does a prokaryotic cell survive without cell organelles ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net .
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whats the difference between cytosol and cytoplasm ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) .
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how do smooth er help detoxify area such as the liver ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net .
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hoe does the cytoplasm help with cellar respiration ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) .
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if a prokaryotic cell has no organelles , how does it carry out life processes ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship .
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when was the endosymbiotic theory thought of ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle .
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how does the nucleolus form inside of the nucleus ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed .
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why do disposal enzymes work only when the ph is 5 ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself .
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why are there ribosomes in the rough , but not soft er ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) .
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why does the number of smooth endoplasmic reticulum vary within cells ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus .
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in the process , glycosylation , why is the protein generally tagged with a carbohydrate ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it .
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if a vesicle forms on the cell membrane , does it still release what it was going to release outside of the cell ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found .
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what is the difference between nucleoplasm and cytoplasm ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship .
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are the endosymbiosis theory and the endosymbiotic theory the same thing ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria .
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in the 13th paragraph , what process produces atp in the cells , and where is most of this energy created ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) .
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how does the rough endoplasmic reticulum help distinguish whether cells should leave or remain in the cell ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle .
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how does the nucleolus stay separated from the nucleus without a bound membrane ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) .
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how many different carbohydrates are tagged to proteins on the rough endoplasmic reticulum ?
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what is a cell right now your body is doing a million things at once . it ’ s sending electrical impulses , pumping blood , filtering urine , digesting food , making protein , storing fat , and that ’ s just the stuff you ’ re not thinking about ! you can do all this because you are made of cells — tiny units of life that are like specialized factories , full of machinery designed to accomplish the business of life . cells make up every living thing , from blue whales to the archaebacteria that live inside volcanos . just like the organisms they make up , cells can come in all shapes and sizes . nerve cells in giant squids can reach up to 12m [ 39 ft ] in length , while human eggs ( the largest human cells ) are about 0.1mm across . plant cells have protective walls made of cellulose ( which also makes up the strings in celery that make it so hard to eat ) while fungal cell walls are made from the same stuff as lobster shells . however , despite this vast range in size , shape , and function , all these little factories have the same basic machinery . there are two main types of cells , prokaryotic and eukaryotic . prokaryotes are cells that do not have membrane bound nuclei , whereas eukaryotes do . the rest of our discussion will strictly be on eukaryotes . think about what a factory needs in order to function effectively . at its most basic , a factory needs a building , a product , and a way to make that product . all cells have membranes ( the building ) , dna ( the various blueprints ) , and ribosomes ( the production line ) , and so are able to make proteins ( the product - let ’ s say we ’ re making toys ) . this article will focus on eukaryotes , since they are the cell type that contains organelles . what ’ s found inside a cell an organelle ( think of it as a cell ’ s internal organ ) is a membrane bound structure found within a cell . just like cells have membranes to hold everything in , these mini-organs are also bound in a double layer of phospholipids to insulate their little compartments within the larger cells . you can think of organelles as smaller rooms within the factory , with specialized conditions to help these rooms carry out their specific task ( like a break room stocked with goodies or a research room with cool gadgets and a special air filter ) . these organelles are found in the cytoplasm , a viscous liquid found within the cell membrane that houses the organelles and is the location of most of the action happening in a cell . below is a table of the organelles found in the basic human cell , which we ’ ll be using as our template for this discussion . organelle | function | factory part : - : | : - : | : - : nucleus | dna storage | room where the blueprints are kept mitochondrion | energy production | powerplant smooth endoplasmic reticulum ( ser ) | lipid production ; detoxification | accessory production - makes decorations for the toy , etc . rough endoplasmic reticulum ( rer ) | protein production ; in particular for export out of the cell | primary production line - makes the toys golgi apparatus | protein modification and export | shipping department peroxisome | lipid destruction ; contains oxidative enzymes | security and waste removal lysosome | protein destruction | recycling and security nucleus our dna has the blueprints for every protein in our body , all packaged into a neat double helix . the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info . this membrane is actually a set of two lipid bilayers , so there are four sheets of lipids separating the inside of the nucleus from the cytoplasm . the space between the two bilayers is known as the perinuclear space . though part of the function of the nucleus is to separate the dna from the rest of the cell , molecules must still be able to move in and out ( e.g. , rna ) . proteins channels known as nuclear pores form holes in the nuclear envelope . the nucleus itself is filled with liquid ( called nucleoplasm ) and is similar in structure and function to cytoplasm . it is here within the nucleoplasm where chromosomes ( tightly packed strands of dna containing all our blueprints ) are found . a nucleus has interesting implications for how a cell responds to its environment . thanks to the added protection of the nuclear envelope , the dna is a little bit more secure from enzymes , pathogens , and potentially harmful products of fat and protein metabolism . since this is the only permanent copy of the instructions the cell has , it is very important to keep the dna in good condition . if the dna was not sequestered away , it would be vulnerable to damage by the aforementioned dangers , which would then lead to defective protein production . imagine a giant hole or coffee stain in the blueprint for your toy - all of a sudden you don ’ t have either enough or the right information to make a critical piece of the toy . the nuclear envelope also keeps molecules responsible for dna transcription and repair close to the dna itself - otherwise those molecules would diffuse across the entire cell and it would take a lot more work and luck to get anything done ! while transcription ( making a complementary strand of rna from dna ) is completed within the nucleus , translation ( making protein from rna instructions ) takes place in the cytoplasm . if there was no barrier between the transcription and translation machineries , it ’ s possible that poorly-made or unfinished rna would get turned into poorly made and potentially dangerous proteins . before an rna can exit the nucleus to be translated , it must get special modifications , in the form of a cap and tail at either end of the molecule , that act as a stamp of approval to let the cell know this piece of rna is complete and properly made . nucleolus within the nucleus is a small subspace known as the nucleolus . it is not bound by a membrane , so it is not an organelle . this space forms near the part of dna with instructions for making ribosomes , the molecules responsible for making proteins . ribosomes are assembled in the nucleolus , and exit the nucleus with nuclear pores . in our analogy , the robots making our product are made in a special corner of the blueprint room , before being released to the factory . endoplasmic reticulum endoplasmic means inside ( endo ) the cytoplasm ( plasm ) . reticulum comes from the latin word for net . basically , an endoplasmic reticulum is a plasma membrane found inside the cell that folds in on itself to create an internal space known as the lumen . this lumen is actually continuous with the perinuclear space , so we know the endoplasmic reticulum is attached to the nuclear envelope . there are actually two different endoplasmic reticuli in a cell : the smooth endoplasmic reticulum and the rough endoplasmic reticulum . the rough endoplasmic reticulum is the site of protein production ( where we make our major product - the toy ) while the smooth endoplasmic reticulum is where lipids ( fats ) are made ( accessories for the toy , but not the central product of the factory ) . rough endoplasmic reticulum the rough endoplasmic reticulum is so-called because its surface is studded with ribosomes , the molecules in charge of protein production . when a ribosome finds a specific rna segment , that segment may tell the ribosome to travel to the rough endoplasmic reticulum and embed itself . the protein created from this segment will find itself inside the lumen of the rough endoplasmic reticulum , where it folds and is tagged with a ( usually carbohydrate ) molecule in a process known as glycosylation that marks the protein for transport to the golgi apparatus . the rough endoplasmic reticulum is continuous with the nuclear envelope , and looks like a series of canals near the nucleus . proteins made in the rough endoplasmic reticulum as destined to either be a part of a membrane , or to be secreted from the cell membrane out of the cell . without an rough endoplasmic reticulum , it would be a lot harder to distinguish between proteins that should leave the cell , and proteins that should remain . thus , the rough endoplasmic reticulum helps cells specialize and allows for greater complexity in the organism . smooth endoplasmic reticulum the smooth endoplasmic reticulum makes lipids and steroids , instead of being involved in protein synthesis . these are fat-based molecules that are important in energy storage , membrane structure , and communication ( steroids can act as hormones ) . the smooth endoplasmic reticulum is also responsible for detoxifying the cell . it is more tubular than the rough endoplasmic reticulum , and is not necessarily continuous with the nuclear envelope . every cell has a smooth endoplasmic reticulum , but the amount will vary with cell function . for example , the liver , which is responsible for most of the body ’ s detoxification , has a larger amount of smooth endoplasmic reticulum . golgi apparatus ( aka golgi body aka golgi ) we mentioned the golgi apparatus earlier when we discussed the production of proteins in the rough endoplasmic reticulum . if the smooth and rough endoplasmic reticula are how we make our product , the golgi is the mailroom that sends our product to customers . it is responsible for packing proteins from the rough endoplasmic reticulum into membrane-bound vesicles ( tiny compartments of lipid bilayer that store molecules ) which then translocate to the cell membrane . at the cell membrane , the vesicles can fuse with the larger lipid bilayer , causing the vesicle contents to either become part of the cell membrane or be released to the outside . different molecules actually have different fates upon entering the golgi . this determination is done by tagging the proteins with special sugar molecules that act as a shipping label for the protein . the shipping department identifies the molecule and sets it on one of 4 paths : cytosol : the proteins that enter the golgi by mistake are sent back into the cytosol ( imagine the barcode scanning wrong and the item being returned ) . cell membrane : proteins destined for the cell membrane are processed continuously . once the vesicle is made , it moves to the cell membrane and fuses with it . molecules in this pathway are often protein channels which allow molecules into or out of the cell , or cell identifiers which project into the extracellular space and act like a name tag for the cell . secretion : some proteins are meant to be secreted from the cell to act on other parts of the body . before these vesicles can fuse with the cell membrane , they must accumulate in number , and require a special chemical signal to be released . this way shipments only go out if they ’ re worth the cost of sending them ( you generally wouldn ’ t ship just one toy and expect to profit ) . lysosome : the final destination for proteins coming through the golgi is the lysosome . vesicles sent to this acidic organelle contain enzymes that will hydrolyze the lysosome ’ s content . lysosome the lysosome is the cell ’ s recycling center . these organelles are spheres full of enzymes ready to hydrolyze ( chop up the chemical bonds of ) whatever substance crosses the membrane , so the cell can reuse the raw material . these disposal enzymes only function properly in environments with a ph of 5 , two orders of magnitude more acidic than the cell ’ s internal ph of 7 . lysosomal proteins only being active in an acidic environment acts as safety mechanism for the rest of the cell - if the lysosome were to somehow leak or burst , the degradative enzymes would inactivate before they chopped up proteins the cell still needed . peroxisome like the lysosome , the peroxisome is a spherical organelle responsible for destroying its contents . unlike the lysosome , which mostly degrades proteins , the peroxisome is the site of fatty acid breakdown . it also protects the cell from reactive oxygen species ( ros ) molecules which could seriously damage the cell . ross are molecules like oxygen ions or peroxides that are created as a byproduct of normal cellular metabolism , but also by radiation , tobacco , and drugs . they cause what is known as oxidative stress in the cell by reacting with and damaging dna and lipid-based molecules like cell membranes . these ross are the reason we need antioxidants in our diet . mitochondria just like a factory can ’ t run without electricity , a cell can ’ t run without energy . atp ( adenosine triphosphate ) is the energy currency of the cell , and is produced in a process known as cellular respiration . though the process begins in the cytoplasm , the bulk of the energy produced comes from later steps that take place in the mitochondria . like we saw with the nuclear envelope , there are actually two lipid bilayers that separate the mitochondrial contents from the cytoplasm . we refer to them as the inner and outer mitochondrial membranes . if we cross both membranes we end up in the matrix , where pyruvate is sent after it is created from the breakdown of glucose ( this is step 1 of cellular respiration , known as glycolysis ) .the space between the two membranes is called the intermembrane space , and it has a low ph ( is acidic ) because the electron transport chain embedded in the inner membrane pumps protons ( h+ ) into it . energy to make atp comes from protons moving back into the matrix down their gradient from the intermembrane space . mitochondria are also somewhat unique in that they are self-replicating and have their own dna , almost as if they were a completely separate cell . the prevailing theory , known as the endosymbiotic theory , is that eukaryotes were first formed by large prokaryotic cells engulfing smaller cells that looked a lot like mitochondria ( and chloroplasts , more on them later ) . instead of being digested , the engulfed cells remained intact and the arrangement turned out to be advantageous to both cells , which created a symbiotic relationship . so far we ’ ve discussed organelles , the membrane-bound structures within a cell that have some sort of specialized function . now let ’ s take a moment to talk about the scaffolding that ’ s holding all of this in place - the walls and beams of our factory . cytoskeleton within the cytoplasm there is network of protein fibers known as the cytoskeleton . this structure is responsible for both cell movement and stability . the major components of the cytoskeleton are microtubules , intermediate filaments , and microfilaments . microtubules microtubules are small tubes made from the protein tubulin . these tubules are found in cilia and flagella , structures involved in cell movement . they also help provide pathways for secretory vesicles to move through the cell , and are even involved in cell division as they are a part of the mitotic spindle , which pulls homologous chromosomes apart . intermediate filaments smaller than the microtubules , but larger than the microfilaments , the intermediate filaments are made of a variety of proteins such as keratin and/or neurofilament . they are very stable , and help provide structure to the nuclear envelope and anchor organelles . microfilaments microfilaments are the thinnest part of the cytoskeleton , and are made of actin [ a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells ] . actin is both flexible and strong , making it a useful protein in cell movement . in the heart , contraction is mediated through an actin-myosin system . plants and platelets so far we ’ ve covered basic organelles found in a eukaryotic cell . however , not every cell has each of these organelles , and some cells have organelles we haven ’ t discussed . for example , plant cells have chloroplasts , organelles that resemble mitochondria and are responsible for turning sunlight into useful energy for the cell ( this is like factories that are powered by energy they collect via solar panels ) . on the other hand , platelets , blood cells responsible for clotting , have no nucleus and are in fact just fragments of cytoplasm contained within a cell membrane . eukaryotes vs bacteria vs archaea it is also important to keep in mind that organelles are found only in eukaryotes , one of the three major cell divisions . the other two major divisions , bacteria and archaea are known as prokaryotes , and have no membrane bound organelles within . consider the following : some diseases can be traced back to organelle lack / malformation . for example , inclusion-cell ( i-cell ) disease occurs due to a defect in the golgi . in order to mark enzymes that should be sent to lysosomes to help degrade unwanted molecules , the golgi has to bind them with a mannose 6-phosphate tag , like a shipping label . however , in patients with i-cell disease , one of the proteins that make this tag is mutated , and can not do its job , like a broken label machine . this means that proteins can not be targeted to lysosomes . these untagged proteins are the enzymes that are responsible for chopping up other proteins . what happens is the inactivated enzymes end up being sent outside the cell , while lysosomes clog up with undigested material . this disease is congenital , and usually fatal before patients reach 7 years of age . an interesting idea is that mitochondria can be used to trace maternal ancestry . since mitochondria are self-replicating and have their own dna , they are not determined by the genes found in the nucleus . instead , your mitochondria have developed from the mitochondria present in the female ovum ( egg ) that you developed from . defects in mitochondrial dna cause hereditary diseases that pass only from mother to children .
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the processes to transform dna into proteins are known as transcription and translation , and happen in different compartments within the cell . the first step , transcription , happens in the nucleus , which holds our dna . a membrane called the nuclear envelope surrounds the nucleus , and its job is to create a room within the cell to both protect the genetic information and to house all the molecules that are involved in processing and protecting that info .
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how does the nucleus protect the dna inside of it ?
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