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connection between $ i^2 = -1 $ and where $ i $ lives we began our study of complex numbers by inventing a number $ i $ that satisfies $ i^2 = -1 $ , and later visualized it by placing it outside the number line , one unit above $ 0 $ . with the visualizations offered in the last article , we can now see why that point in space is such a natural home for a number whose square is $ -1 $ . you see , multiplication by $ i $ gives a $ 90^\circ $ rotation about the origin : you can think about this either because $ i $ has absolute value $ 1 $ and angle $ 90^\circ $ , or because this rotation is the only way to move the grid around ( fixing $ 0 $ ) which places $ 1 $ on the spot where $ i $ started off . so what happens if we multiply everything in the plane by $ i $ twice ? it is the same as a $ 180^\circ $ rotation about the origin , which is multiplication by $ -1 $ . this of course makes sense , because multiplying by $ i $ twice is the same as multiplying by $ i^2 $ , which should be $ -1 $ . it is interesting to think about how if we had tried to place $ i $ somewhere else while still maintaining its characteristic quality that $ i^2 = -1 $ , we could not have had such a clean visualization for complex multiplication . powers of complex numbers let 's play around some more with repeatedly multiplying by some complex number . example 1 : $ ( 1 + i\sqrt { 3 } ) ^3 $ take the number $ z = 1 + i\sqrt { 3 } $ , which has absolute value $ \sqrt { 1^2 + ( \sqrt { 3 } ) ^2 } = 2 $ , and angle $ 60^\circ $ . what happens if we multiply everything on the plane by $ z $ three times in a row ? everything is stretched by a factor of $ 2 $ three times , and so is ultimately stretched by a factor of $ 2^3 = 8 $ . likewise everything is rotated by $ 60^\circ $ three times in a row , so is ultimately rotated by $ 180^\circ $ . hence , at the end it 's the same as multiplying by $ -8 $ , so $ ( 1 + i\sqrt { 3 } ) ^3 = -8 $ . we can also see this using algebra as follows : $ \begin { align } & amp ; \phantom { = } \left ( 2 ( \cos ( 60^\circ ) + i\sin ( 60^\circ ) ) \right ) ^3\\ & amp ; = 2^3 ( \cos ( 60^\circ + 60^\circ + 60^\circ ) + i\sin ( 60^\circ + 60^\circ + 60^\circ ) \\\ & amp ; = 8 ( \cos ( 180^\circ ) + i\sin ( 180^\circ ) ) \\ & amp ; = -8 \end { align } $ example 2 : $ ( 1 + i ) ^8 $ next , suppose we multiply everything on the plane by $ ( 1 + i ) $ eight successive times : since the magnitude of $ 1 + i $ is $ |1 + i| = \sqrt { 1^2 + 1^2 } = \sqrt { 2 } $ , everything is stretched by a factor of $ \sqrt { 2 } $ eight times , and hence is ultimately stretched by a factor of $ ( \sqrt { 2 } ) ^8 = 2^4 = 16 $ . since the angle of $ ( 1 + i ) $ is $ 45^\circ $ , everything is ultimately rotated by $ 8 \cdot 45^\circ = 360^\circ $ , so in total it 's as if we did n't rotate at all . therefore $ ( 1 + i ) ^8 = 16 $ . alternatively , the way to see this with algebra is $ \begin { align } & amp ; \phantom { = } ( 1 + i ) ^8 \\ & amp ; = \left ( \sqrt { 2 } \cdot ( \cos ( 45^\circ ) + i \sin ( 45^\circ ) \right ) ^8 \ & amp ; = ( \sqrt { 2 } ) ^8 \cdot \left ( \cos ( \underbrace { 45^\circ + \cdots + 45^\circ } { \text { $ 8 $ times } } ) + i\sin ( \underbrace { 45^\circ + \cdots + 45^\circ } { \text { $ 8 $ times } } ) \right ) \\ & amp ; = 16 \left ( \cos ( 360^\circ ) + i\sin ( 360^\circ ) \right ) \\ & amp ; = 16 \end { align } $ example 3 : $ z^5 = 1 $ now let 's start asking the reverse question : is there a number $ z $ such that after multiplying everything in the plane by $ z $ five successive times , things are back to where they started ? in other words , can we solve the equation $ z^5 = 1 $ ? one simple answer is $ z = 1 $ , but let 's see if we can find any others . first off , the magnitude of such a number would have to be $ 1 $ , since if it were more than $ 1 $ , the plane would keep stretching , and if it were less than $ 1 $ , it would keep shrinking . rotation is a different animal , though , since you can get back to where you started after repeating certain rotations . in particular , if you rotate $ \dfrac { 1 } { 5 } $ of the way around , like this then doing this $ 5 $ successive times will bring you back to where you started . the number which rotates the plane in this way is $ \cos ( 72^\circ ) + i\sin ( 72^\circ ) $ , since $ \dfrac { 360^\circ } { 5 } = 72^\circ $ . there are also other solutions , such as rotating $ \dfrac { 2 } { 5 } $ of the way around : or $ \dfrac { 1 } { 5 } $ of the way around the other way : in fact , beautifully , the numbers which solve the equation form a perfect pentagon on the unit circle : example 4 : $ z^6 = -27 $ looking at the equation $ z^6 = -27 $ , it is asking us to find a complex number $ z $ such that multiplying by this number $ 6 $ successive times will stretch by a factor of $ 27 $ , and rotate by $ 180^\circ $ , since the negative indicates $ 180^\circ $ rotation . something which will stretch by a factor of $ 27 $ after $ 6 $ applications must have magnitude $ \sqrt [ 6 ] { 27 } = \sqrt { 3 } $ , and one way to rotate which gives $ 180^\circ $ after $ 6 $ applications is to rotate by $ \dfrac { 180^\circ } { 6 } = 30^\circ $ . therefore one number that solves this equation $ z^6 = -27 $ is $ \begin { align } \sqrt { 3 } ( \cos ( 30^\circ ) + i\sin ( 30^\circ ) ) & amp ; = \sqrt { 3 } \left ( \frac { \sqrt { 3 } } { 2 } + i \frac { 1 } { 2 } \right ) \ & amp ; = \frac { 3 } { 2 } + i \frac { \sqrt { 3 } } { 2 } \end { align } $ however , there are also other answers ! in fact , those answers form a perfect hexagon on the circle with radius $ \sqrt { 3 } $ : can you see why ? solving $ z^n= w $ in general let 's generalize the last two examples . if you are given values $ w $ and $ n $ , and asked to solve for $ z $ , as in the last example where $ n=6 $ and $ w = -27 $ , you first find the polar representation of $ w $ : $ w = r ( \cos ( \theta ) + i\sin ( \theta ) ) $ this means the angle of $ z $ must be $ \dfrac { \theta } { n } $ , and it 's magnitude must be $ \sqrt [ n ] { r } $ , since this way multiplying by $ z $ a total of $ n $ succesive times will in effect rotate by $ \theta $ and scale by $ r $ , just as $ w $ does , so $ z = \sqrt [ n ] { r } \cdot \left ( \cos\left ( \dfrac { \theta } { n } \right ) + i\sin\left ( \dfrac { \theta } { n } \right ) \right ) $ to find the other solutions , we keep in mind that the angle $ \theta $ could have been thought of as $ \theta + 2\pi $ , or $ \theta + 4\pi $ , or $ \theta + 2k\pi $ for any integer $ k $ , since these are all really the same angle . the reason this matters is because it can affect the value of $ \dfrac { \theta } { n } $ if we replace $ \theta $ with $ \theta + 2\pi k $ before dividing . hence all the answers will be of the form $ z = \sqrt [ n ] { r } \cdot \left ( \cos\left ( \dfrac { \theta + 2k\pi } { n } \right ) + i\sin\left ( \dfrac { \theta + 2k\pi } { n } \right ) \right ) $ for some integer value of $ k $ . these values will be different as $ k $ ranges from $ 0 $ to $ n-1 $ , but once $ k=n $ we can note that the angle $ \dfrac { \theta + 2n\pi } { n } = \dfrac { \theta } { n } + 2\pi $ is really the same as $ \dfrac { \theta } { n } $ , since they differ by one full rotation . therefore one sees all the answers just by considering values of $ k $ ranging from $ 0 $ to $ n-1 $ .
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hence all the answers will be of the form $ z = \sqrt [ n ] { r } \cdot \left ( \cos\left ( \dfrac { \theta + 2k\pi } { n } \right ) + i\sin\left ( \dfrac { \theta + 2k\pi } { n } \right ) \right ) $ for some integer value of $ k $ . these values will be different as $ k $ ranges from $ 0 $ to $ n-1 $ , but once $ k=n $ we can note that the angle $ \dfrac { \theta + 2n\pi } { n } = \dfrac { \theta } { n } + 2\pi $ is really the same as $ \dfrac { \theta } { n } $ , since they differ by one full rotation . therefore one sees all the answers just by considering values of $ k $ ranging from $ 0 $ to $ n-1 $ .
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where does n-1 come from ?
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connection between $ i^2 = -1 $ and where $ i $ lives we began our study of complex numbers by inventing a number $ i $ that satisfies $ i^2 = -1 $ , and later visualized it by placing it outside the number line , one unit above $ 0 $ . with the visualizations offered in the last article , we can now see why that point in space is such a natural home for a number whose square is $ -1 $ . you see , multiplication by $ i $ gives a $ 90^\circ $ rotation about the origin : you can think about this either because $ i $ has absolute value $ 1 $ and angle $ 90^\circ $ , or because this rotation is the only way to move the grid around ( fixing $ 0 $ ) which places $ 1 $ on the spot where $ i $ started off . so what happens if we multiply everything in the plane by $ i $ twice ? it is the same as a $ 180^\circ $ rotation about the origin , which is multiplication by $ -1 $ . this of course makes sense , because multiplying by $ i $ twice is the same as multiplying by $ i^2 $ , which should be $ -1 $ . it is interesting to think about how if we had tried to place $ i $ somewhere else while still maintaining its characteristic quality that $ i^2 = -1 $ , we could not have had such a clean visualization for complex multiplication . powers of complex numbers let 's play around some more with repeatedly multiplying by some complex number . example 1 : $ ( 1 + i\sqrt { 3 } ) ^3 $ take the number $ z = 1 + i\sqrt { 3 } $ , which has absolute value $ \sqrt { 1^2 + ( \sqrt { 3 } ) ^2 } = 2 $ , and angle $ 60^\circ $ . what happens if we multiply everything on the plane by $ z $ three times in a row ? everything is stretched by a factor of $ 2 $ three times , and so is ultimately stretched by a factor of $ 2^3 = 8 $ . likewise everything is rotated by $ 60^\circ $ three times in a row , so is ultimately rotated by $ 180^\circ $ . hence , at the end it 's the same as multiplying by $ -8 $ , so $ ( 1 + i\sqrt { 3 } ) ^3 = -8 $ . we can also see this using algebra as follows : $ \begin { align } & amp ; \phantom { = } \left ( 2 ( \cos ( 60^\circ ) + i\sin ( 60^\circ ) ) \right ) ^3\\ & amp ; = 2^3 ( \cos ( 60^\circ + 60^\circ + 60^\circ ) + i\sin ( 60^\circ + 60^\circ + 60^\circ ) \\\ & amp ; = 8 ( \cos ( 180^\circ ) + i\sin ( 180^\circ ) ) \\ & amp ; = -8 \end { align } $ example 2 : $ ( 1 + i ) ^8 $ next , suppose we multiply everything on the plane by $ ( 1 + i ) $ eight successive times : since the magnitude of $ 1 + i $ is $ |1 + i| = \sqrt { 1^2 + 1^2 } = \sqrt { 2 } $ , everything is stretched by a factor of $ \sqrt { 2 } $ eight times , and hence is ultimately stretched by a factor of $ ( \sqrt { 2 } ) ^8 = 2^4 = 16 $ . since the angle of $ ( 1 + i ) $ is $ 45^\circ $ , everything is ultimately rotated by $ 8 \cdot 45^\circ = 360^\circ $ , so in total it 's as if we did n't rotate at all . therefore $ ( 1 + i ) ^8 = 16 $ . alternatively , the way to see this with algebra is $ \begin { align } & amp ; \phantom { = } ( 1 + i ) ^8 \\ & amp ; = \left ( \sqrt { 2 } \cdot ( \cos ( 45^\circ ) + i \sin ( 45^\circ ) \right ) ^8 \ & amp ; = ( \sqrt { 2 } ) ^8 \cdot \left ( \cos ( \underbrace { 45^\circ + \cdots + 45^\circ } { \text { $ 8 $ times } } ) + i\sin ( \underbrace { 45^\circ + \cdots + 45^\circ } { \text { $ 8 $ times } } ) \right ) \\ & amp ; = 16 \left ( \cos ( 360^\circ ) + i\sin ( 360^\circ ) \right ) \\ & amp ; = 16 \end { align } $ example 3 : $ z^5 = 1 $ now let 's start asking the reverse question : is there a number $ z $ such that after multiplying everything in the plane by $ z $ five successive times , things are back to where they started ? in other words , can we solve the equation $ z^5 = 1 $ ? one simple answer is $ z = 1 $ , but let 's see if we can find any others . first off , the magnitude of such a number would have to be $ 1 $ , since if it were more than $ 1 $ , the plane would keep stretching , and if it were less than $ 1 $ , it would keep shrinking . rotation is a different animal , though , since you can get back to where you started after repeating certain rotations . in particular , if you rotate $ \dfrac { 1 } { 5 } $ of the way around , like this then doing this $ 5 $ successive times will bring you back to where you started . the number which rotates the plane in this way is $ \cos ( 72^\circ ) + i\sin ( 72^\circ ) $ , since $ \dfrac { 360^\circ } { 5 } = 72^\circ $ . there are also other solutions , such as rotating $ \dfrac { 2 } { 5 } $ of the way around : or $ \dfrac { 1 } { 5 } $ of the way around the other way : in fact , beautifully , the numbers which solve the equation form a perfect pentagon on the unit circle : example 4 : $ z^6 = -27 $ looking at the equation $ z^6 = -27 $ , it is asking us to find a complex number $ z $ such that multiplying by this number $ 6 $ successive times will stretch by a factor of $ 27 $ , and rotate by $ 180^\circ $ , since the negative indicates $ 180^\circ $ rotation . something which will stretch by a factor of $ 27 $ after $ 6 $ applications must have magnitude $ \sqrt [ 6 ] { 27 } = \sqrt { 3 } $ , and one way to rotate which gives $ 180^\circ $ after $ 6 $ applications is to rotate by $ \dfrac { 180^\circ } { 6 } = 30^\circ $ . therefore one number that solves this equation $ z^6 = -27 $ is $ \begin { align } \sqrt { 3 } ( \cos ( 30^\circ ) + i\sin ( 30^\circ ) ) & amp ; = \sqrt { 3 } \left ( \frac { \sqrt { 3 } } { 2 } + i \frac { 1 } { 2 } \right ) \ & amp ; = \frac { 3 } { 2 } + i \frac { \sqrt { 3 } } { 2 } \end { align } $ however , there are also other answers ! in fact , those answers form a perfect hexagon on the circle with radius $ \sqrt { 3 } $ : can you see why ? solving $ z^n= w $ in general let 's generalize the last two examples . if you are given values $ w $ and $ n $ , and asked to solve for $ z $ , as in the last example where $ n=6 $ and $ w = -27 $ , you first find the polar representation of $ w $ : $ w = r ( \cos ( \theta ) + i\sin ( \theta ) ) $ this means the angle of $ z $ must be $ \dfrac { \theta } { n } $ , and it 's magnitude must be $ \sqrt [ n ] { r } $ , since this way multiplying by $ z $ a total of $ n $ succesive times will in effect rotate by $ \theta $ and scale by $ r $ , just as $ w $ does , so $ z = \sqrt [ n ] { r } \cdot \left ( \cos\left ( \dfrac { \theta } { n } \right ) + i\sin\left ( \dfrac { \theta } { n } \right ) \right ) $ to find the other solutions , we keep in mind that the angle $ \theta $ could have been thought of as $ \theta + 2\pi $ , or $ \theta + 4\pi $ , or $ \theta + 2k\pi $ for any integer $ k $ , since these are all really the same angle . the reason this matters is because it can affect the value of $ \dfrac { \theta } { n } $ if we replace $ \theta $ with $ \theta + 2\pi k $ before dividing . hence all the answers will be of the form $ z = \sqrt [ n ] { r } \cdot \left ( \cos\left ( \dfrac { \theta + 2k\pi } { n } \right ) + i\sin\left ( \dfrac { \theta + 2k\pi } { n } \right ) \right ) $ for some integer value of $ k $ . these values will be different as $ k $ ranges from $ 0 $ to $ n-1 $ , but once $ k=n $ we can note that the angle $ \dfrac { \theta + 2n\pi } { n } = \dfrac { \theta } { n } + 2\pi $ is really the same as $ \dfrac { \theta } { n } $ , since they differ by one full rotation . therefore one sees all the answers just by considering values of $ k $ ranging from $ 0 $ to $ n-1 $ .
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if you are given values $ w $ and $ n $ , and asked to solve for $ z $ , as in the last example where $ n=6 $ and $ w = -27 $ , you first find the polar representation of $ w $ : $ w = r ( \cos ( \theta ) + i\sin ( \theta ) ) $ this means the angle of $ z $ must be $ \dfrac { \theta } { n } $ , and it 's magnitude must be $ \sqrt [ n ] { r } $ , since this way multiplying by $ z $ a total of $ n $ succesive times will in effect rotate by $ \theta $ and scale by $ r $ , just as $ w $ does , so $ z = \sqrt [ n ] { r } \cdot \left ( \cos\left ( \dfrac { \theta } { n } \right ) + i\sin\left ( \dfrac { \theta } { n } \right ) \right ) $ to find the other solutions , we keep in mind that the angle $ \theta $ could have been thought of as $ \theta + 2\pi $ , or $ \theta + 4\pi $ , or $ \theta + 2k\pi $ for any integer $ k $ , since these are all really the same angle . the reason this matters is because it can affect the value of $ \dfrac { \theta } { n } $ if we replace $ \theta $ with $ \theta + 2\pi k $ before dividing . hence all the answers will be of the form $ z = \sqrt [ n ] { r } \cdot \left ( \cos\left ( \dfrac { \theta + 2k\pi } { n } \right ) + i\sin\left ( \dfrac { \theta + 2k\pi } { n } \right ) \right ) $ for some integer value of $ k $ . these values will be different as $ k $ ranges from $ 0 $ to $ n-1 $ , but once $ k=n $ we can note that the angle $ \dfrac { \theta + 2n\pi } { n } = \dfrac { \theta } { n } + 2\pi $ is really the same as $ \dfrac { \theta } { n } $ , since they differ by one full rotation .
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why is pi in there ?
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key points : when a population is in hardy-weinberg equilibrium for a gene , it is not evolving , and allele frequencies will stay the same across generations . there are five basic hardy-weinberg assumptions : no mutation , random mating , no gene flow , infinite population size , and no selection . if the assumptions are not met for a gene , the population may evolve for that gene ( the gene 's allele frequencies may change ) . mechanisms of evolution correspond to violations of different hardy-weinberg assumptions . they are : mutation , non-random mating , gene flow , finite population size ( genetic drift ) , and natural selection . introduction in nature , populations are usually evolving . the grass in an open meadow , the wolves in a forest , and even the bacteria in a person 's body are all natural populations . and all of these populations are likely to be evolving for at least some of their genes . evolution is happing right here , right now ! to be clear , that does n't mean these populations are marching towards some final state of perfection . all evolution means is that a population is changing in its genetic makeup over generations . and the changes may be subtle—for instance , in a wolf population , there might be a shift in the frequency of a gene variant for black rather than gray fur . sometimes , this type of change is due to natural selection . other times , it comes from migration of new organisms into the population , or from random events—the evolutionary `` luck of the draw . '' in this article , we 'll examine what it means for a population evolve , see the ( rarely met ) set of conditions required for a population not to evolve , and explore how failure to meet these conditions does in fact lead to evolution . hardy-weinberg equilibrium first , let 's see what it looks like when a population is not evolving . if a population is in a state called hardy-weinberg equilibrium , the frequencies of alleles , or gene versions , and genotypes , or sets of alleles , in that population will stay the same over generations ( and will also satisfy the hardy-weinberg equation ) . formally , evolution is a change in allele frequencies in a population over time , so a population in hardy-weinberg equilibrium is not evolving . that 's a little bit abstract , so let 's break it down using an example . imagine we have a large population of beetles . in fact , just for the heck of it , let 's say this population is infinitely large . the beetles of our infinitely large population come in two colors , dark gray and light gray , and their color is determined by the a gene . aa and aa beetles are dark gray , and aa beetles are light gray . in our population , let 's say that the a allele has a frequency of $ 0.3 $ , while the a allele has a frequency of $ 0.7 $ . if a population is in hardy-weinberg equilibrium , allele frequencies will be related to genotype frequencies by a specific mathematical relationship , the hardy-weinberg equation . so , we can predict the genotype frequencies we 'd expect to see ( if the population is in hardy-weinberg equilibrium ) by plugging in allele frequencies as shown below : let 's imagine that these are , in fact , the genotype frequencies we see in our beetle population ( $ 9\ % $ aa , $ 42\ % $ aa , $ 49\ % $ aa ) . excellent—our beetles appear to be in hardy-weinberg equilibrium ! now , let 's imagine that the beetles reproduce to make a next generation . what will the allele and genotype frequencies will be in that generation ? to predict this , we need to make a few assumptions : first , let 's assume that none of the genotypes is any better than the others at surviving or getting mates . if this is the case , the frequency of a and a alleles in the pool of gametes ( sperm and eggs ) that meet to make the next generation will be the same as the overall frequency of each allele in the present generation . second , let 's assume that the beetles mate randomly ( as opposed to , say , black beetles preferring other black beetles ) . if this is the case , we can think of reproduction as the result of two random events : selection of a sperm from the population 's gene pool and selection of an egg from the same gene pool . the probability of getting any offspring genotype is just the probability of getting the egg and sperm combo ( s ) that produce that genotype . we can use a modified punnett square to represent the likelihood of getting different offspring genotypes . here , we multiply the frequencies of the gametes on the axes to get the probability of the fertilization events in the squares : as shown above , we 'd predict an offspring generation with the exact same genotype frequencies as the parent generation : $ 9\ % $ aa , $ 42\ % $ aa , and $ 49\ % $ aa . if genotype frequencies have not changed , we also must have the same allele frequencies as in the parent generation : $ 0.3 $ for a and $ 0.7 $ for a . what we 've just seen is the essence of hardy-weinberg equilibrium . if alleles in the gamete pool exactly mirror those in the parent generation , and if they meet up randomly ( in an infinitely large number of events ) , there is no reason—in fact , no way—for allele and genotype frequencies to change from one generation to the next . in the absence of other factors , you can imagine this process repeating over and over , generation after generation , keeping allele and genotype frequencies the same . since evolution is a change in allele frequencies in a population over generations , a population in hardy-weinberg equilibrium is , by definition , not evolving . but is that realistic ? as we mentioned at the beginning of the article , populations are usually not in hardy-weinberg equilibrium ( at least , not for all of the genes in their genome ) . instead , populations tend to evolve : the allele frequencies of at least some of their genes change from one generation to the next . in fact , population geneticists often check to see if a population is in hardy-weinberg equilibrium because they suspect other forces may be at work . if the population ’ s allele and genotype frequencies are changing over generations ( or if the allele and genotype frequencies do n't match the predictions of the hardy-weinberg equation ) , the race is on to find out why . hardy-weinberg assumptions and evolution what causes populations to evolve ? in order for a population to be in hardy-weinberg equilibrium , or a non-evolving state , it must meet five major assumptions : no mutation . no new alleles are generated by mutation , nor are genes duplicated or deleted . random mating . organisms mate randomly with each other , with no preference for particular genotypes . no gene flow . neither individuals nor their gametes ( e.g. , windborne pollen ) enter or exit the population . very large population size . the population should be effectively infinite in size . no natural selection . all alleles confer equal fitness ( make organisms equally likely to survive and reproduce ) . if any one of these assumptions is not met , the population will not be in hardy-weinberg equilibrium . instead , it may evolve : allele frequencies may change from one generation to the next . allele and genotype frequencies within a single generation may also fail to satisfy the hardy-weinberg equation . some genes may satisfy hardy-weinberg , while others do not note that we can think about hardy-weinberg equilibrium in two ways : for just one gene , or for all the genes in the genome . if we look at just one gene , we check whether the above criteria are true for that one gene . for example , we would ask if there were mutations in that gene , or if organisms mated randomly with regards to their genotype for that gene . if we look at all the genes in the genome , the conditions have to be met for every single gene . while it ’ s possible that the conditions will be more or less met for a single gene under certain circumstances , it ’ s very unlikely that they would be met for all the genes in the genome . so , while a population may be in hardy-weinberg equilibrium for some genes ( not evolving for those genes ) , it ’ s unlikely to be in hardy-weinberg equilibrium for all of its genes ( not evolving at all ) . mechanisms of evolution different hardy-weinberg assumptions , when violated , correspond to different mechanisms of evolution . mutation . although mutation is the original source of all genetic variation , mutation rate for most organisms is pretty low . so , the impact of brand-new mutations on allele frequencies from one generation to the next is usually not large . ( however , natural selection acting on the results of a mutation can be a powerful mechanism of evolution ! ) non-random mating . in non-random mating , organisms may prefer to mate with others of the same genotype or of different genotypes . non-random mating wo n't make allele frequencies in the population change by itself , though it can alter genotype frequencies . this keeps the population from being in hardy-weinberg equilibrium , but it ’ s debatable whether it counts as evolution , since the allele frequencies are staying the same . gene flow . gene flow involves the movement of genes into or out of a population , due to either the movement of individual organisms or their gametes ( eggs and sperm , e.g. , through pollen dispersal by a plant ) . organisms and gametes that enter a population may have new alleles , or may bring in existing alleles but in different proportions than those already in the population . gene flow can be a strong agent of evolution . non-infinite population size ( genetic drift ) . genetic drift involves changes in allele frequency due to chance events – literally , `` sampling error '' in selecting alleles for the next generation . drift can occur in any population of non-infinite size , but it has a stronger effect on small populations . we will look in detail at genetic drift and the effects of population size . natural selection . finally , the most famous mechanism of evolution ! natural selection occurs when one allele ( or combination of alleles of different genes ) makes an organism more or less fit , that is , able to survive and reproduce in a given environment . if an allele reduces fitness , its frequency will tend to drop from one generation to the next . we will look in detail at different forms of natural selection that occur in populations . all five of the above mechanisms of evolution may act to some extent in any natural population . in fact , the evolutionary trajectory of a given gene ( that is , how its alleles change in frequency in the population across generations ) may result from several evolutionary mechanisms acting at once . for instance , one gene ’ s allele frequencies might be modified by both gene flow and genetic drift . for another gene , mutation may produce a new allele , which is then favored ( or disfavored ) by natural selection .
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in our population , let 's say that the a allele has a frequency of $ 0.3 $ , while the a allele has a frequency of $ 0.7 $ . if a population is in hardy-weinberg equilibrium , allele frequencies will be related to genotype frequencies by a specific mathematical relationship , the hardy-weinberg equation . so , we can predict the genotype frequencies we 'd expect to see ( if the population is in hardy-weinberg equilibrium ) by plugging in allele frequencies as shown below : let 's imagine that these are , in fact , the genotype frequencies we see in our beetle population ( $ 9\ % $ aa , $ 42\ % $ aa , $ 49\ % $ aa ) .
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what is the point of using the hardy weinberg equation if there is no population that fits the conditions anyways ?
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key points : when a population is in hardy-weinberg equilibrium for a gene , it is not evolving , and allele frequencies will stay the same across generations . there are five basic hardy-weinberg assumptions : no mutation , random mating , no gene flow , infinite population size , and no selection . if the assumptions are not met for a gene , the population may evolve for that gene ( the gene 's allele frequencies may change ) . mechanisms of evolution correspond to violations of different hardy-weinberg assumptions . they are : mutation , non-random mating , gene flow , finite population size ( genetic drift ) , and natural selection . introduction in nature , populations are usually evolving . the grass in an open meadow , the wolves in a forest , and even the bacteria in a person 's body are all natural populations . and all of these populations are likely to be evolving for at least some of their genes . evolution is happing right here , right now ! to be clear , that does n't mean these populations are marching towards some final state of perfection . all evolution means is that a population is changing in its genetic makeup over generations . and the changes may be subtle—for instance , in a wolf population , there might be a shift in the frequency of a gene variant for black rather than gray fur . sometimes , this type of change is due to natural selection . other times , it comes from migration of new organisms into the population , or from random events—the evolutionary `` luck of the draw . '' in this article , we 'll examine what it means for a population evolve , see the ( rarely met ) set of conditions required for a population not to evolve , and explore how failure to meet these conditions does in fact lead to evolution . hardy-weinberg equilibrium first , let 's see what it looks like when a population is not evolving . if a population is in a state called hardy-weinberg equilibrium , the frequencies of alleles , or gene versions , and genotypes , or sets of alleles , in that population will stay the same over generations ( and will also satisfy the hardy-weinberg equation ) . formally , evolution is a change in allele frequencies in a population over time , so a population in hardy-weinberg equilibrium is not evolving . that 's a little bit abstract , so let 's break it down using an example . imagine we have a large population of beetles . in fact , just for the heck of it , let 's say this population is infinitely large . the beetles of our infinitely large population come in two colors , dark gray and light gray , and their color is determined by the a gene . aa and aa beetles are dark gray , and aa beetles are light gray . in our population , let 's say that the a allele has a frequency of $ 0.3 $ , while the a allele has a frequency of $ 0.7 $ . if a population is in hardy-weinberg equilibrium , allele frequencies will be related to genotype frequencies by a specific mathematical relationship , the hardy-weinberg equation . so , we can predict the genotype frequencies we 'd expect to see ( if the population is in hardy-weinberg equilibrium ) by plugging in allele frequencies as shown below : let 's imagine that these are , in fact , the genotype frequencies we see in our beetle population ( $ 9\ % $ aa , $ 42\ % $ aa , $ 49\ % $ aa ) . excellent—our beetles appear to be in hardy-weinberg equilibrium ! now , let 's imagine that the beetles reproduce to make a next generation . what will the allele and genotype frequencies will be in that generation ? to predict this , we need to make a few assumptions : first , let 's assume that none of the genotypes is any better than the others at surviving or getting mates . if this is the case , the frequency of a and a alleles in the pool of gametes ( sperm and eggs ) that meet to make the next generation will be the same as the overall frequency of each allele in the present generation . second , let 's assume that the beetles mate randomly ( as opposed to , say , black beetles preferring other black beetles ) . if this is the case , we can think of reproduction as the result of two random events : selection of a sperm from the population 's gene pool and selection of an egg from the same gene pool . the probability of getting any offspring genotype is just the probability of getting the egg and sperm combo ( s ) that produce that genotype . we can use a modified punnett square to represent the likelihood of getting different offspring genotypes . here , we multiply the frequencies of the gametes on the axes to get the probability of the fertilization events in the squares : as shown above , we 'd predict an offspring generation with the exact same genotype frequencies as the parent generation : $ 9\ % $ aa , $ 42\ % $ aa , and $ 49\ % $ aa . if genotype frequencies have not changed , we also must have the same allele frequencies as in the parent generation : $ 0.3 $ for a and $ 0.7 $ for a . what we 've just seen is the essence of hardy-weinberg equilibrium . if alleles in the gamete pool exactly mirror those in the parent generation , and if they meet up randomly ( in an infinitely large number of events ) , there is no reason—in fact , no way—for allele and genotype frequencies to change from one generation to the next . in the absence of other factors , you can imagine this process repeating over and over , generation after generation , keeping allele and genotype frequencies the same . since evolution is a change in allele frequencies in a population over generations , a population in hardy-weinberg equilibrium is , by definition , not evolving . but is that realistic ? as we mentioned at the beginning of the article , populations are usually not in hardy-weinberg equilibrium ( at least , not for all of the genes in their genome ) . instead , populations tend to evolve : the allele frequencies of at least some of their genes change from one generation to the next . in fact , population geneticists often check to see if a population is in hardy-weinberg equilibrium because they suspect other forces may be at work . if the population ’ s allele and genotype frequencies are changing over generations ( or if the allele and genotype frequencies do n't match the predictions of the hardy-weinberg equation ) , the race is on to find out why . hardy-weinberg assumptions and evolution what causes populations to evolve ? in order for a population to be in hardy-weinberg equilibrium , or a non-evolving state , it must meet five major assumptions : no mutation . no new alleles are generated by mutation , nor are genes duplicated or deleted . random mating . organisms mate randomly with each other , with no preference for particular genotypes . no gene flow . neither individuals nor their gametes ( e.g. , windborne pollen ) enter or exit the population . very large population size . the population should be effectively infinite in size . no natural selection . all alleles confer equal fitness ( make organisms equally likely to survive and reproduce ) . if any one of these assumptions is not met , the population will not be in hardy-weinberg equilibrium . instead , it may evolve : allele frequencies may change from one generation to the next . allele and genotype frequencies within a single generation may also fail to satisfy the hardy-weinberg equation . some genes may satisfy hardy-weinberg , while others do not note that we can think about hardy-weinberg equilibrium in two ways : for just one gene , or for all the genes in the genome . if we look at just one gene , we check whether the above criteria are true for that one gene . for example , we would ask if there were mutations in that gene , or if organisms mated randomly with regards to their genotype for that gene . if we look at all the genes in the genome , the conditions have to be met for every single gene . while it ’ s possible that the conditions will be more or less met for a single gene under certain circumstances , it ’ s very unlikely that they would be met for all the genes in the genome . so , while a population may be in hardy-weinberg equilibrium for some genes ( not evolving for those genes ) , it ’ s unlikely to be in hardy-weinberg equilibrium for all of its genes ( not evolving at all ) . mechanisms of evolution different hardy-weinberg assumptions , when violated , correspond to different mechanisms of evolution . mutation . although mutation is the original source of all genetic variation , mutation rate for most organisms is pretty low . so , the impact of brand-new mutations on allele frequencies from one generation to the next is usually not large . ( however , natural selection acting on the results of a mutation can be a powerful mechanism of evolution ! ) non-random mating . in non-random mating , organisms may prefer to mate with others of the same genotype or of different genotypes . non-random mating wo n't make allele frequencies in the population change by itself , though it can alter genotype frequencies . this keeps the population from being in hardy-weinberg equilibrium , but it ’ s debatable whether it counts as evolution , since the allele frequencies are staying the same . gene flow . gene flow involves the movement of genes into or out of a population , due to either the movement of individual organisms or their gametes ( eggs and sperm , e.g. , through pollen dispersal by a plant ) . organisms and gametes that enter a population may have new alleles , or may bring in existing alleles but in different proportions than those already in the population . gene flow can be a strong agent of evolution . non-infinite population size ( genetic drift ) . genetic drift involves changes in allele frequency due to chance events – literally , `` sampling error '' in selecting alleles for the next generation . drift can occur in any population of non-infinite size , but it has a stronger effect on small populations . we will look in detail at genetic drift and the effects of population size . natural selection . finally , the most famous mechanism of evolution ! natural selection occurs when one allele ( or combination of alleles of different genes ) makes an organism more or less fit , that is , able to survive and reproduce in a given environment . if an allele reduces fitness , its frequency will tend to drop from one generation to the next . we will look in detail at different forms of natural selection that occur in populations . all five of the above mechanisms of evolution may act to some extent in any natural population . in fact , the evolutionary trajectory of a given gene ( that is , how its alleles change in frequency in the population across generations ) may result from several evolutionary mechanisms acting at once . for instance , one gene ’ s allele frequencies might be modified by both gene flow and genetic drift . for another gene , mutation may produce a new allele , which is then favored ( or disfavored ) by natural selection .
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so , while a population may be in hardy-weinberg equilibrium for some genes ( not evolving for those genes ) , it ’ s unlikely to be in hardy-weinberg equilibrium for all of its genes ( not evolving at all ) . mechanisms of evolution different hardy-weinberg assumptions , when violated , correspond to different mechanisms of evolution . mutation .
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how does evolution unify the biological sciences ?
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key points : when a population is in hardy-weinberg equilibrium for a gene , it is not evolving , and allele frequencies will stay the same across generations . there are five basic hardy-weinberg assumptions : no mutation , random mating , no gene flow , infinite population size , and no selection . if the assumptions are not met for a gene , the population may evolve for that gene ( the gene 's allele frequencies may change ) . mechanisms of evolution correspond to violations of different hardy-weinberg assumptions . they are : mutation , non-random mating , gene flow , finite population size ( genetic drift ) , and natural selection . introduction in nature , populations are usually evolving . the grass in an open meadow , the wolves in a forest , and even the bacteria in a person 's body are all natural populations . and all of these populations are likely to be evolving for at least some of their genes . evolution is happing right here , right now ! to be clear , that does n't mean these populations are marching towards some final state of perfection . all evolution means is that a population is changing in its genetic makeup over generations . and the changes may be subtle—for instance , in a wolf population , there might be a shift in the frequency of a gene variant for black rather than gray fur . sometimes , this type of change is due to natural selection . other times , it comes from migration of new organisms into the population , or from random events—the evolutionary `` luck of the draw . '' in this article , we 'll examine what it means for a population evolve , see the ( rarely met ) set of conditions required for a population not to evolve , and explore how failure to meet these conditions does in fact lead to evolution . hardy-weinberg equilibrium first , let 's see what it looks like when a population is not evolving . if a population is in a state called hardy-weinberg equilibrium , the frequencies of alleles , or gene versions , and genotypes , or sets of alleles , in that population will stay the same over generations ( and will also satisfy the hardy-weinberg equation ) . formally , evolution is a change in allele frequencies in a population over time , so a population in hardy-weinberg equilibrium is not evolving . that 's a little bit abstract , so let 's break it down using an example . imagine we have a large population of beetles . in fact , just for the heck of it , let 's say this population is infinitely large . the beetles of our infinitely large population come in two colors , dark gray and light gray , and their color is determined by the a gene . aa and aa beetles are dark gray , and aa beetles are light gray . in our population , let 's say that the a allele has a frequency of $ 0.3 $ , while the a allele has a frequency of $ 0.7 $ . if a population is in hardy-weinberg equilibrium , allele frequencies will be related to genotype frequencies by a specific mathematical relationship , the hardy-weinberg equation . so , we can predict the genotype frequencies we 'd expect to see ( if the population is in hardy-weinberg equilibrium ) by plugging in allele frequencies as shown below : let 's imagine that these are , in fact , the genotype frequencies we see in our beetle population ( $ 9\ % $ aa , $ 42\ % $ aa , $ 49\ % $ aa ) . excellent—our beetles appear to be in hardy-weinberg equilibrium ! now , let 's imagine that the beetles reproduce to make a next generation . what will the allele and genotype frequencies will be in that generation ? to predict this , we need to make a few assumptions : first , let 's assume that none of the genotypes is any better than the others at surviving or getting mates . if this is the case , the frequency of a and a alleles in the pool of gametes ( sperm and eggs ) that meet to make the next generation will be the same as the overall frequency of each allele in the present generation . second , let 's assume that the beetles mate randomly ( as opposed to , say , black beetles preferring other black beetles ) . if this is the case , we can think of reproduction as the result of two random events : selection of a sperm from the population 's gene pool and selection of an egg from the same gene pool . the probability of getting any offspring genotype is just the probability of getting the egg and sperm combo ( s ) that produce that genotype . we can use a modified punnett square to represent the likelihood of getting different offspring genotypes . here , we multiply the frequencies of the gametes on the axes to get the probability of the fertilization events in the squares : as shown above , we 'd predict an offspring generation with the exact same genotype frequencies as the parent generation : $ 9\ % $ aa , $ 42\ % $ aa , and $ 49\ % $ aa . if genotype frequencies have not changed , we also must have the same allele frequencies as in the parent generation : $ 0.3 $ for a and $ 0.7 $ for a . what we 've just seen is the essence of hardy-weinberg equilibrium . if alleles in the gamete pool exactly mirror those in the parent generation , and if they meet up randomly ( in an infinitely large number of events ) , there is no reason—in fact , no way—for allele and genotype frequencies to change from one generation to the next . in the absence of other factors , you can imagine this process repeating over and over , generation after generation , keeping allele and genotype frequencies the same . since evolution is a change in allele frequencies in a population over generations , a population in hardy-weinberg equilibrium is , by definition , not evolving . but is that realistic ? as we mentioned at the beginning of the article , populations are usually not in hardy-weinberg equilibrium ( at least , not for all of the genes in their genome ) . instead , populations tend to evolve : the allele frequencies of at least some of their genes change from one generation to the next . in fact , population geneticists often check to see if a population is in hardy-weinberg equilibrium because they suspect other forces may be at work . if the population ’ s allele and genotype frequencies are changing over generations ( or if the allele and genotype frequencies do n't match the predictions of the hardy-weinberg equation ) , the race is on to find out why . hardy-weinberg assumptions and evolution what causes populations to evolve ? in order for a population to be in hardy-weinberg equilibrium , or a non-evolving state , it must meet five major assumptions : no mutation . no new alleles are generated by mutation , nor are genes duplicated or deleted . random mating . organisms mate randomly with each other , with no preference for particular genotypes . no gene flow . neither individuals nor their gametes ( e.g. , windborne pollen ) enter or exit the population . very large population size . the population should be effectively infinite in size . no natural selection . all alleles confer equal fitness ( make organisms equally likely to survive and reproduce ) . if any one of these assumptions is not met , the population will not be in hardy-weinberg equilibrium . instead , it may evolve : allele frequencies may change from one generation to the next . allele and genotype frequencies within a single generation may also fail to satisfy the hardy-weinberg equation . some genes may satisfy hardy-weinberg , while others do not note that we can think about hardy-weinberg equilibrium in two ways : for just one gene , or for all the genes in the genome . if we look at just one gene , we check whether the above criteria are true for that one gene . for example , we would ask if there were mutations in that gene , or if organisms mated randomly with regards to their genotype for that gene . if we look at all the genes in the genome , the conditions have to be met for every single gene . while it ’ s possible that the conditions will be more or less met for a single gene under certain circumstances , it ’ s very unlikely that they would be met for all the genes in the genome . so , while a population may be in hardy-weinberg equilibrium for some genes ( not evolving for those genes ) , it ’ s unlikely to be in hardy-weinberg equilibrium for all of its genes ( not evolving at all ) . mechanisms of evolution different hardy-weinberg assumptions , when violated , correspond to different mechanisms of evolution . mutation . although mutation is the original source of all genetic variation , mutation rate for most organisms is pretty low . so , the impact of brand-new mutations on allele frequencies from one generation to the next is usually not large . ( however , natural selection acting on the results of a mutation can be a powerful mechanism of evolution ! ) non-random mating . in non-random mating , organisms may prefer to mate with others of the same genotype or of different genotypes . non-random mating wo n't make allele frequencies in the population change by itself , though it can alter genotype frequencies . this keeps the population from being in hardy-weinberg equilibrium , but it ’ s debatable whether it counts as evolution , since the allele frequencies are staying the same . gene flow . gene flow involves the movement of genes into or out of a population , due to either the movement of individual organisms or their gametes ( eggs and sperm , e.g. , through pollen dispersal by a plant ) . organisms and gametes that enter a population may have new alleles , or may bring in existing alleles but in different proportions than those already in the population . gene flow can be a strong agent of evolution . non-infinite population size ( genetic drift ) . genetic drift involves changes in allele frequency due to chance events – literally , `` sampling error '' in selecting alleles for the next generation . drift can occur in any population of non-infinite size , but it has a stronger effect on small populations . we will look in detail at genetic drift and the effects of population size . natural selection . finally , the most famous mechanism of evolution ! natural selection occurs when one allele ( or combination of alleles of different genes ) makes an organism more or less fit , that is , able to survive and reproduce in a given environment . if an allele reduces fitness , its frequency will tend to drop from one generation to the next . we will look in detail at different forms of natural selection that occur in populations . all five of the above mechanisms of evolution may act to some extent in any natural population . in fact , the evolutionary trajectory of a given gene ( that is , how its alleles change in frequency in the population across generations ) may result from several evolutionary mechanisms acting at once . for instance , one gene ’ s allele frequencies might be modified by both gene flow and genetic drift . for another gene , mutation may produce a new allele , which is then favored ( or disfavored ) by natural selection .
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no new alleles are generated by mutation , nor are genes duplicated or deleted . random mating . organisms mate randomly with each other , with no preference for particular genotypes .
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in the conditions for the hardy-weinberg equilibrium , how does random mating stabilize the allele frequency ?
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key points : when a population is in hardy-weinberg equilibrium for a gene , it is not evolving , and allele frequencies will stay the same across generations . there are five basic hardy-weinberg assumptions : no mutation , random mating , no gene flow , infinite population size , and no selection . if the assumptions are not met for a gene , the population may evolve for that gene ( the gene 's allele frequencies may change ) . mechanisms of evolution correspond to violations of different hardy-weinberg assumptions . they are : mutation , non-random mating , gene flow , finite population size ( genetic drift ) , and natural selection . introduction in nature , populations are usually evolving . the grass in an open meadow , the wolves in a forest , and even the bacteria in a person 's body are all natural populations . and all of these populations are likely to be evolving for at least some of their genes . evolution is happing right here , right now ! to be clear , that does n't mean these populations are marching towards some final state of perfection . all evolution means is that a population is changing in its genetic makeup over generations . and the changes may be subtle—for instance , in a wolf population , there might be a shift in the frequency of a gene variant for black rather than gray fur . sometimes , this type of change is due to natural selection . other times , it comes from migration of new organisms into the population , or from random events—the evolutionary `` luck of the draw . '' in this article , we 'll examine what it means for a population evolve , see the ( rarely met ) set of conditions required for a population not to evolve , and explore how failure to meet these conditions does in fact lead to evolution . hardy-weinberg equilibrium first , let 's see what it looks like when a population is not evolving . if a population is in a state called hardy-weinberg equilibrium , the frequencies of alleles , or gene versions , and genotypes , or sets of alleles , in that population will stay the same over generations ( and will also satisfy the hardy-weinberg equation ) . formally , evolution is a change in allele frequencies in a population over time , so a population in hardy-weinberg equilibrium is not evolving . that 's a little bit abstract , so let 's break it down using an example . imagine we have a large population of beetles . in fact , just for the heck of it , let 's say this population is infinitely large . the beetles of our infinitely large population come in two colors , dark gray and light gray , and their color is determined by the a gene . aa and aa beetles are dark gray , and aa beetles are light gray . in our population , let 's say that the a allele has a frequency of $ 0.3 $ , while the a allele has a frequency of $ 0.7 $ . if a population is in hardy-weinberg equilibrium , allele frequencies will be related to genotype frequencies by a specific mathematical relationship , the hardy-weinberg equation . so , we can predict the genotype frequencies we 'd expect to see ( if the population is in hardy-weinberg equilibrium ) by plugging in allele frequencies as shown below : let 's imagine that these are , in fact , the genotype frequencies we see in our beetle population ( $ 9\ % $ aa , $ 42\ % $ aa , $ 49\ % $ aa ) . excellent—our beetles appear to be in hardy-weinberg equilibrium ! now , let 's imagine that the beetles reproduce to make a next generation . what will the allele and genotype frequencies will be in that generation ? to predict this , we need to make a few assumptions : first , let 's assume that none of the genotypes is any better than the others at surviving or getting mates . if this is the case , the frequency of a and a alleles in the pool of gametes ( sperm and eggs ) that meet to make the next generation will be the same as the overall frequency of each allele in the present generation . second , let 's assume that the beetles mate randomly ( as opposed to , say , black beetles preferring other black beetles ) . if this is the case , we can think of reproduction as the result of two random events : selection of a sperm from the population 's gene pool and selection of an egg from the same gene pool . the probability of getting any offspring genotype is just the probability of getting the egg and sperm combo ( s ) that produce that genotype . we can use a modified punnett square to represent the likelihood of getting different offspring genotypes . here , we multiply the frequencies of the gametes on the axes to get the probability of the fertilization events in the squares : as shown above , we 'd predict an offspring generation with the exact same genotype frequencies as the parent generation : $ 9\ % $ aa , $ 42\ % $ aa , and $ 49\ % $ aa . if genotype frequencies have not changed , we also must have the same allele frequencies as in the parent generation : $ 0.3 $ for a and $ 0.7 $ for a . what we 've just seen is the essence of hardy-weinberg equilibrium . if alleles in the gamete pool exactly mirror those in the parent generation , and if they meet up randomly ( in an infinitely large number of events ) , there is no reason—in fact , no way—for allele and genotype frequencies to change from one generation to the next . in the absence of other factors , you can imagine this process repeating over and over , generation after generation , keeping allele and genotype frequencies the same . since evolution is a change in allele frequencies in a population over generations , a population in hardy-weinberg equilibrium is , by definition , not evolving . but is that realistic ? as we mentioned at the beginning of the article , populations are usually not in hardy-weinberg equilibrium ( at least , not for all of the genes in their genome ) . instead , populations tend to evolve : the allele frequencies of at least some of their genes change from one generation to the next . in fact , population geneticists often check to see if a population is in hardy-weinberg equilibrium because they suspect other forces may be at work . if the population ’ s allele and genotype frequencies are changing over generations ( or if the allele and genotype frequencies do n't match the predictions of the hardy-weinberg equation ) , the race is on to find out why . hardy-weinberg assumptions and evolution what causes populations to evolve ? in order for a population to be in hardy-weinberg equilibrium , or a non-evolving state , it must meet five major assumptions : no mutation . no new alleles are generated by mutation , nor are genes duplicated or deleted . random mating . organisms mate randomly with each other , with no preference for particular genotypes . no gene flow . neither individuals nor their gametes ( e.g. , windborne pollen ) enter or exit the population . very large population size . the population should be effectively infinite in size . no natural selection . all alleles confer equal fitness ( make organisms equally likely to survive and reproduce ) . if any one of these assumptions is not met , the population will not be in hardy-weinberg equilibrium . instead , it may evolve : allele frequencies may change from one generation to the next . allele and genotype frequencies within a single generation may also fail to satisfy the hardy-weinberg equation . some genes may satisfy hardy-weinberg , while others do not note that we can think about hardy-weinberg equilibrium in two ways : for just one gene , or for all the genes in the genome . if we look at just one gene , we check whether the above criteria are true for that one gene . for example , we would ask if there were mutations in that gene , or if organisms mated randomly with regards to their genotype for that gene . if we look at all the genes in the genome , the conditions have to be met for every single gene . while it ’ s possible that the conditions will be more or less met for a single gene under certain circumstances , it ’ s very unlikely that they would be met for all the genes in the genome . so , while a population may be in hardy-weinberg equilibrium for some genes ( not evolving for those genes ) , it ’ s unlikely to be in hardy-weinberg equilibrium for all of its genes ( not evolving at all ) . mechanisms of evolution different hardy-weinberg assumptions , when violated , correspond to different mechanisms of evolution . mutation . although mutation is the original source of all genetic variation , mutation rate for most organisms is pretty low . so , the impact of brand-new mutations on allele frequencies from one generation to the next is usually not large . ( however , natural selection acting on the results of a mutation can be a powerful mechanism of evolution ! ) non-random mating . in non-random mating , organisms may prefer to mate with others of the same genotype or of different genotypes . non-random mating wo n't make allele frequencies in the population change by itself , though it can alter genotype frequencies . this keeps the population from being in hardy-weinberg equilibrium , but it ’ s debatable whether it counts as evolution , since the allele frequencies are staying the same . gene flow . gene flow involves the movement of genes into or out of a population , due to either the movement of individual organisms or their gametes ( eggs and sperm , e.g. , through pollen dispersal by a plant ) . organisms and gametes that enter a population may have new alleles , or may bring in existing alleles but in different proportions than those already in the population . gene flow can be a strong agent of evolution . non-infinite population size ( genetic drift ) . genetic drift involves changes in allele frequency due to chance events – literally , `` sampling error '' in selecting alleles for the next generation . drift can occur in any population of non-infinite size , but it has a stronger effect on small populations . we will look in detail at genetic drift and the effects of population size . natural selection . finally , the most famous mechanism of evolution ! natural selection occurs when one allele ( or combination of alleles of different genes ) makes an organism more or less fit , that is , able to survive and reproduce in a given environment . if an allele reduces fitness , its frequency will tend to drop from one generation to the next . we will look in detail at different forms of natural selection that occur in populations . all five of the above mechanisms of evolution may act to some extent in any natural population . in fact , the evolutionary trajectory of a given gene ( that is , how its alleles change in frequency in the population across generations ) may result from several evolutionary mechanisms acting at once . for instance , one gene ’ s allele frequencies might be modified by both gene flow and genetic drift . for another gene , mutation may produce a new allele , which is then favored ( or disfavored ) by natural selection .
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aa and aa beetles are dark gray , and aa beetles are light gray . in our population , let 's say that the a allele has a frequency of $ 0.3 $ , while the a allele has a frequency of $ 0.7 $ . if a population is in hardy-weinberg equilibrium , allele frequencies will be related to genotype frequencies by a specific mathematical relationship , the hardy-weinberg equation .
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could you say that the frequency of the dominant trait stays constant ?
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key points : when a population is in hardy-weinberg equilibrium for a gene , it is not evolving , and allele frequencies will stay the same across generations . there are five basic hardy-weinberg assumptions : no mutation , random mating , no gene flow , infinite population size , and no selection . if the assumptions are not met for a gene , the population may evolve for that gene ( the gene 's allele frequencies may change ) . mechanisms of evolution correspond to violations of different hardy-weinberg assumptions . they are : mutation , non-random mating , gene flow , finite population size ( genetic drift ) , and natural selection . introduction in nature , populations are usually evolving . the grass in an open meadow , the wolves in a forest , and even the bacteria in a person 's body are all natural populations . and all of these populations are likely to be evolving for at least some of their genes . evolution is happing right here , right now ! to be clear , that does n't mean these populations are marching towards some final state of perfection . all evolution means is that a population is changing in its genetic makeup over generations . and the changes may be subtle—for instance , in a wolf population , there might be a shift in the frequency of a gene variant for black rather than gray fur . sometimes , this type of change is due to natural selection . other times , it comes from migration of new organisms into the population , or from random events—the evolutionary `` luck of the draw . '' in this article , we 'll examine what it means for a population evolve , see the ( rarely met ) set of conditions required for a population not to evolve , and explore how failure to meet these conditions does in fact lead to evolution . hardy-weinberg equilibrium first , let 's see what it looks like when a population is not evolving . if a population is in a state called hardy-weinberg equilibrium , the frequencies of alleles , or gene versions , and genotypes , or sets of alleles , in that population will stay the same over generations ( and will also satisfy the hardy-weinberg equation ) . formally , evolution is a change in allele frequencies in a population over time , so a population in hardy-weinberg equilibrium is not evolving . that 's a little bit abstract , so let 's break it down using an example . imagine we have a large population of beetles . in fact , just for the heck of it , let 's say this population is infinitely large . the beetles of our infinitely large population come in two colors , dark gray and light gray , and their color is determined by the a gene . aa and aa beetles are dark gray , and aa beetles are light gray . in our population , let 's say that the a allele has a frequency of $ 0.3 $ , while the a allele has a frequency of $ 0.7 $ . if a population is in hardy-weinberg equilibrium , allele frequencies will be related to genotype frequencies by a specific mathematical relationship , the hardy-weinberg equation . so , we can predict the genotype frequencies we 'd expect to see ( if the population is in hardy-weinberg equilibrium ) by plugging in allele frequencies as shown below : let 's imagine that these are , in fact , the genotype frequencies we see in our beetle population ( $ 9\ % $ aa , $ 42\ % $ aa , $ 49\ % $ aa ) . excellent—our beetles appear to be in hardy-weinberg equilibrium ! now , let 's imagine that the beetles reproduce to make a next generation . what will the allele and genotype frequencies will be in that generation ? to predict this , we need to make a few assumptions : first , let 's assume that none of the genotypes is any better than the others at surviving or getting mates . if this is the case , the frequency of a and a alleles in the pool of gametes ( sperm and eggs ) that meet to make the next generation will be the same as the overall frequency of each allele in the present generation . second , let 's assume that the beetles mate randomly ( as opposed to , say , black beetles preferring other black beetles ) . if this is the case , we can think of reproduction as the result of two random events : selection of a sperm from the population 's gene pool and selection of an egg from the same gene pool . the probability of getting any offspring genotype is just the probability of getting the egg and sperm combo ( s ) that produce that genotype . we can use a modified punnett square to represent the likelihood of getting different offspring genotypes . here , we multiply the frequencies of the gametes on the axes to get the probability of the fertilization events in the squares : as shown above , we 'd predict an offspring generation with the exact same genotype frequencies as the parent generation : $ 9\ % $ aa , $ 42\ % $ aa , and $ 49\ % $ aa . if genotype frequencies have not changed , we also must have the same allele frequencies as in the parent generation : $ 0.3 $ for a and $ 0.7 $ for a . what we 've just seen is the essence of hardy-weinberg equilibrium . if alleles in the gamete pool exactly mirror those in the parent generation , and if they meet up randomly ( in an infinitely large number of events ) , there is no reason—in fact , no way—for allele and genotype frequencies to change from one generation to the next . in the absence of other factors , you can imagine this process repeating over and over , generation after generation , keeping allele and genotype frequencies the same . since evolution is a change in allele frequencies in a population over generations , a population in hardy-weinberg equilibrium is , by definition , not evolving . but is that realistic ? as we mentioned at the beginning of the article , populations are usually not in hardy-weinberg equilibrium ( at least , not for all of the genes in their genome ) . instead , populations tend to evolve : the allele frequencies of at least some of their genes change from one generation to the next . in fact , population geneticists often check to see if a population is in hardy-weinberg equilibrium because they suspect other forces may be at work . if the population ’ s allele and genotype frequencies are changing over generations ( or if the allele and genotype frequencies do n't match the predictions of the hardy-weinberg equation ) , the race is on to find out why . hardy-weinberg assumptions and evolution what causes populations to evolve ? in order for a population to be in hardy-weinberg equilibrium , or a non-evolving state , it must meet five major assumptions : no mutation . no new alleles are generated by mutation , nor are genes duplicated or deleted . random mating . organisms mate randomly with each other , with no preference for particular genotypes . no gene flow . neither individuals nor their gametes ( e.g. , windborne pollen ) enter or exit the population . very large population size . the population should be effectively infinite in size . no natural selection . all alleles confer equal fitness ( make organisms equally likely to survive and reproduce ) . if any one of these assumptions is not met , the population will not be in hardy-weinberg equilibrium . instead , it may evolve : allele frequencies may change from one generation to the next . allele and genotype frequencies within a single generation may also fail to satisfy the hardy-weinberg equation . some genes may satisfy hardy-weinberg , while others do not note that we can think about hardy-weinberg equilibrium in two ways : for just one gene , or for all the genes in the genome . if we look at just one gene , we check whether the above criteria are true for that one gene . for example , we would ask if there were mutations in that gene , or if organisms mated randomly with regards to their genotype for that gene . if we look at all the genes in the genome , the conditions have to be met for every single gene . while it ’ s possible that the conditions will be more or less met for a single gene under certain circumstances , it ’ s very unlikely that they would be met for all the genes in the genome . so , while a population may be in hardy-weinberg equilibrium for some genes ( not evolving for those genes ) , it ’ s unlikely to be in hardy-weinberg equilibrium for all of its genes ( not evolving at all ) . mechanisms of evolution different hardy-weinberg assumptions , when violated , correspond to different mechanisms of evolution . mutation . although mutation is the original source of all genetic variation , mutation rate for most organisms is pretty low . so , the impact of brand-new mutations on allele frequencies from one generation to the next is usually not large . ( however , natural selection acting on the results of a mutation can be a powerful mechanism of evolution ! ) non-random mating . in non-random mating , organisms may prefer to mate with others of the same genotype or of different genotypes . non-random mating wo n't make allele frequencies in the population change by itself , though it can alter genotype frequencies . this keeps the population from being in hardy-weinberg equilibrium , but it ’ s debatable whether it counts as evolution , since the allele frequencies are staying the same . gene flow . gene flow involves the movement of genes into or out of a population , due to either the movement of individual organisms or their gametes ( eggs and sperm , e.g. , through pollen dispersal by a plant ) . organisms and gametes that enter a population may have new alleles , or may bring in existing alleles but in different proportions than those already in the population . gene flow can be a strong agent of evolution . non-infinite population size ( genetic drift ) . genetic drift involves changes in allele frequency due to chance events – literally , `` sampling error '' in selecting alleles for the next generation . drift can occur in any population of non-infinite size , but it has a stronger effect on small populations . we will look in detail at genetic drift and the effects of population size . natural selection . finally , the most famous mechanism of evolution ! natural selection occurs when one allele ( or combination of alleles of different genes ) makes an organism more or less fit , that is , able to survive and reproduce in a given environment . if an allele reduces fitness , its frequency will tend to drop from one generation to the next . we will look in detail at different forms of natural selection that occur in populations . all five of the above mechanisms of evolution may act to some extent in any natural population . in fact , the evolutionary trajectory of a given gene ( that is , how its alleles change in frequency in the population across generations ) may result from several evolutionary mechanisms acting at once . for instance , one gene ’ s allele frequencies might be modified by both gene flow and genetic drift . for another gene , mutation may produce a new allele , which is then favored ( or disfavored ) by natural selection .
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so , we can predict the genotype frequencies we 'd expect to see ( if the population is in hardy-weinberg equilibrium ) by plugging in allele frequencies as shown below : let 's imagine that these are , in fact , the genotype frequencies we see in our beetle population ( $ 9\ % $ aa , $ 42\ % $ aa , $ 49\ % $ aa ) . excellent—our beetles appear to be in hardy-weinberg equilibrium ! now , let 's imagine that the beetles reproduce to make a next generation .
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for uniparental inheritance , such as mitochondrial dna that we inherit maternally , would hardy-weinberg equilibrium analysis be relevant ?
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key points : when a population is in hardy-weinberg equilibrium for a gene , it is not evolving , and allele frequencies will stay the same across generations . there are five basic hardy-weinberg assumptions : no mutation , random mating , no gene flow , infinite population size , and no selection . if the assumptions are not met for a gene , the population may evolve for that gene ( the gene 's allele frequencies may change ) . mechanisms of evolution correspond to violations of different hardy-weinberg assumptions . they are : mutation , non-random mating , gene flow , finite population size ( genetic drift ) , and natural selection . introduction in nature , populations are usually evolving . the grass in an open meadow , the wolves in a forest , and even the bacteria in a person 's body are all natural populations . and all of these populations are likely to be evolving for at least some of their genes . evolution is happing right here , right now ! to be clear , that does n't mean these populations are marching towards some final state of perfection . all evolution means is that a population is changing in its genetic makeup over generations . and the changes may be subtle—for instance , in a wolf population , there might be a shift in the frequency of a gene variant for black rather than gray fur . sometimes , this type of change is due to natural selection . other times , it comes from migration of new organisms into the population , or from random events—the evolutionary `` luck of the draw . '' in this article , we 'll examine what it means for a population evolve , see the ( rarely met ) set of conditions required for a population not to evolve , and explore how failure to meet these conditions does in fact lead to evolution . hardy-weinberg equilibrium first , let 's see what it looks like when a population is not evolving . if a population is in a state called hardy-weinberg equilibrium , the frequencies of alleles , or gene versions , and genotypes , or sets of alleles , in that population will stay the same over generations ( and will also satisfy the hardy-weinberg equation ) . formally , evolution is a change in allele frequencies in a population over time , so a population in hardy-weinberg equilibrium is not evolving . that 's a little bit abstract , so let 's break it down using an example . imagine we have a large population of beetles . in fact , just for the heck of it , let 's say this population is infinitely large . the beetles of our infinitely large population come in two colors , dark gray and light gray , and their color is determined by the a gene . aa and aa beetles are dark gray , and aa beetles are light gray . in our population , let 's say that the a allele has a frequency of $ 0.3 $ , while the a allele has a frequency of $ 0.7 $ . if a population is in hardy-weinberg equilibrium , allele frequencies will be related to genotype frequencies by a specific mathematical relationship , the hardy-weinberg equation . so , we can predict the genotype frequencies we 'd expect to see ( if the population is in hardy-weinberg equilibrium ) by plugging in allele frequencies as shown below : let 's imagine that these are , in fact , the genotype frequencies we see in our beetle population ( $ 9\ % $ aa , $ 42\ % $ aa , $ 49\ % $ aa ) . excellent—our beetles appear to be in hardy-weinberg equilibrium ! now , let 's imagine that the beetles reproduce to make a next generation . what will the allele and genotype frequencies will be in that generation ? to predict this , we need to make a few assumptions : first , let 's assume that none of the genotypes is any better than the others at surviving or getting mates . if this is the case , the frequency of a and a alleles in the pool of gametes ( sperm and eggs ) that meet to make the next generation will be the same as the overall frequency of each allele in the present generation . second , let 's assume that the beetles mate randomly ( as opposed to , say , black beetles preferring other black beetles ) . if this is the case , we can think of reproduction as the result of two random events : selection of a sperm from the population 's gene pool and selection of an egg from the same gene pool . the probability of getting any offspring genotype is just the probability of getting the egg and sperm combo ( s ) that produce that genotype . we can use a modified punnett square to represent the likelihood of getting different offspring genotypes . here , we multiply the frequencies of the gametes on the axes to get the probability of the fertilization events in the squares : as shown above , we 'd predict an offspring generation with the exact same genotype frequencies as the parent generation : $ 9\ % $ aa , $ 42\ % $ aa , and $ 49\ % $ aa . if genotype frequencies have not changed , we also must have the same allele frequencies as in the parent generation : $ 0.3 $ for a and $ 0.7 $ for a . what we 've just seen is the essence of hardy-weinberg equilibrium . if alleles in the gamete pool exactly mirror those in the parent generation , and if they meet up randomly ( in an infinitely large number of events ) , there is no reason—in fact , no way—for allele and genotype frequencies to change from one generation to the next . in the absence of other factors , you can imagine this process repeating over and over , generation after generation , keeping allele and genotype frequencies the same . since evolution is a change in allele frequencies in a population over generations , a population in hardy-weinberg equilibrium is , by definition , not evolving . but is that realistic ? as we mentioned at the beginning of the article , populations are usually not in hardy-weinberg equilibrium ( at least , not for all of the genes in their genome ) . instead , populations tend to evolve : the allele frequencies of at least some of their genes change from one generation to the next . in fact , population geneticists often check to see if a population is in hardy-weinberg equilibrium because they suspect other forces may be at work . if the population ’ s allele and genotype frequencies are changing over generations ( or if the allele and genotype frequencies do n't match the predictions of the hardy-weinberg equation ) , the race is on to find out why . hardy-weinberg assumptions and evolution what causes populations to evolve ? in order for a population to be in hardy-weinberg equilibrium , or a non-evolving state , it must meet five major assumptions : no mutation . no new alleles are generated by mutation , nor are genes duplicated or deleted . random mating . organisms mate randomly with each other , with no preference for particular genotypes . no gene flow . neither individuals nor their gametes ( e.g. , windborne pollen ) enter or exit the population . very large population size . the population should be effectively infinite in size . no natural selection . all alleles confer equal fitness ( make organisms equally likely to survive and reproduce ) . if any one of these assumptions is not met , the population will not be in hardy-weinberg equilibrium . instead , it may evolve : allele frequencies may change from one generation to the next . allele and genotype frequencies within a single generation may also fail to satisfy the hardy-weinberg equation . some genes may satisfy hardy-weinberg , while others do not note that we can think about hardy-weinberg equilibrium in two ways : for just one gene , or for all the genes in the genome . if we look at just one gene , we check whether the above criteria are true for that one gene . for example , we would ask if there were mutations in that gene , or if organisms mated randomly with regards to their genotype for that gene . if we look at all the genes in the genome , the conditions have to be met for every single gene . while it ’ s possible that the conditions will be more or less met for a single gene under certain circumstances , it ’ s very unlikely that they would be met for all the genes in the genome . so , while a population may be in hardy-weinberg equilibrium for some genes ( not evolving for those genes ) , it ’ s unlikely to be in hardy-weinberg equilibrium for all of its genes ( not evolving at all ) . mechanisms of evolution different hardy-weinberg assumptions , when violated , correspond to different mechanisms of evolution . mutation . although mutation is the original source of all genetic variation , mutation rate for most organisms is pretty low . so , the impact of brand-new mutations on allele frequencies from one generation to the next is usually not large . ( however , natural selection acting on the results of a mutation can be a powerful mechanism of evolution ! ) non-random mating . in non-random mating , organisms may prefer to mate with others of the same genotype or of different genotypes . non-random mating wo n't make allele frequencies in the population change by itself , though it can alter genotype frequencies . this keeps the population from being in hardy-weinberg equilibrium , but it ’ s debatable whether it counts as evolution , since the allele frequencies are staying the same . gene flow . gene flow involves the movement of genes into or out of a population , due to either the movement of individual organisms or their gametes ( eggs and sperm , e.g. , through pollen dispersal by a plant ) . organisms and gametes that enter a population may have new alleles , or may bring in existing alleles but in different proportions than those already in the population . gene flow can be a strong agent of evolution . non-infinite population size ( genetic drift ) . genetic drift involves changes in allele frequency due to chance events – literally , `` sampling error '' in selecting alleles for the next generation . drift can occur in any population of non-infinite size , but it has a stronger effect on small populations . we will look in detail at genetic drift and the effects of population size . natural selection . finally , the most famous mechanism of evolution ! natural selection occurs when one allele ( or combination of alleles of different genes ) makes an organism more or less fit , that is , able to survive and reproduce in a given environment . if an allele reduces fitness , its frequency will tend to drop from one generation to the next . we will look in detail at different forms of natural selection that occur in populations . all five of the above mechanisms of evolution may act to some extent in any natural population . in fact , the evolutionary trajectory of a given gene ( that is , how its alleles change in frequency in the population across generations ) may result from several evolutionary mechanisms acting at once . for instance , one gene ’ s allele frequencies might be modified by both gene flow and genetic drift . for another gene , mutation may produce a new allele , which is then favored ( or disfavored ) by natural selection .
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in non-random mating , organisms may prefer to mate with others of the same genotype or of different genotypes . non-random mating wo n't make allele frequencies in the population change by itself , though it can alter genotype frequencies . this keeps the population from being in hardy-weinberg equilibrium , but it ’ s debatable whether it counts as evolution , since the allele frequencies are staying the same .
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should n't the allele frequencies technically be labeled as allele proportions ?
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key points : when a population is in hardy-weinberg equilibrium for a gene , it is not evolving , and allele frequencies will stay the same across generations . there are five basic hardy-weinberg assumptions : no mutation , random mating , no gene flow , infinite population size , and no selection . if the assumptions are not met for a gene , the population may evolve for that gene ( the gene 's allele frequencies may change ) . mechanisms of evolution correspond to violations of different hardy-weinberg assumptions . they are : mutation , non-random mating , gene flow , finite population size ( genetic drift ) , and natural selection . introduction in nature , populations are usually evolving . the grass in an open meadow , the wolves in a forest , and even the bacteria in a person 's body are all natural populations . and all of these populations are likely to be evolving for at least some of their genes . evolution is happing right here , right now ! to be clear , that does n't mean these populations are marching towards some final state of perfection . all evolution means is that a population is changing in its genetic makeup over generations . and the changes may be subtle—for instance , in a wolf population , there might be a shift in the frequency of a gene variant for black rather than gray fur . sometimes , this type of change is due to natural selection . other times , it comes from migration of new organisms into the population , or from random events—the evolutionary `` luck of the draw . '' in this article , we 'll examine what it means for a population evolve , see the ( rarely met ) set of conditions required for a population not to evolve , and explore how failure to meet these conditions does in fact lead to evolution . hardy-weinberg equilibrium first , let 's see what it looks like when a population is not evolving . if a population is in a state called hardy-weinberg equilibrium , the frequencies of alleles , or gene versions , and genotypes , or sets of alleles , in that population will stay the same over generations ( and will also satisfy the hardy-weinberg equation ) . formally , evolution is a change in allele frequencies in a population over time , so a population in hardy-weinberg equilibrium is not evolving . that 's a little bit abstract , so let 's break it down using an example . imagine we have a large population of beetles . in fact , just for the heck of it , let 's say this population is infinitely large . the beetles of our infinitely large population come in two colors , dark gray and light gray , and their color is determined by the a gene . aa and aa beetles are dark gray , and aa beetles are light gray . in our population , let 's say that the a allele has a frequency of $ 0.3 $ , while the a allele has a frequency of $ 0.7 $ . if a population is in hardy-weinberg equilibrium , allele frequencies will be related to genotype frequencies by a specific mathematical relationship , the hardy-weinberg equation . so , we can predict the genotype frequencies we 'd expect to see ( if the population is in hardy-weinberg equilibrium ) by plugging in allele frequencies as shown below : let 's imagine that these are , in fact , the genotype frequencies we see in our beetle population ( $ 9\ % $ aa , $ 42\ % $ aa , $ 49\ % $ aa ) . excellent—our beetles appear to be in hardy-weinberg equilibrium ! now , let 's imagine that the beetles reproduce to make a next generation . what will the allele and genotype frequencies will be in that generation ? to predict this , we need to make a few assumptions : first , let 's assume that none of the genotypes is any better than the others at surviving or getting mates . if this is the case , the frequency of a and a alleles in the pool of gametes ( sperm and eggs ) that meet to make the next generation will be the same as the overall frequency of each allele in the present generation . second , let 's assume that the beetles mate randomly ( as opposed to , say , black beetles preferring other black beetles ) . if this is the case , we can think of reproduction as the result of two random events : selection of a sperm from the population 's gene pool and selection of an egg from the same gene pool . the probability of getting any offspring genotype is just the probability of getting the egg and sperm combo ( s ) that produce that genotype . we can use a modified punnett square to represent the likelihood of getting different offspring genotypes . here , we multiply the frequencies of the gametes on the axes to get the probability of the fertilization events in the squares : as shown above , we 'd predict an offspring generation with the exact same genotype frequencies as the parent generation : $ 9\ % $ aa , $ 42\ % $ aa , and $ 49\ % $ aa . if genotype frequencies have not changed , we also must have the same allele frequencies as in the parent generation : $ 0.3 $ for a and $ 0.7 $ for a . what we 've just seen is the essence of hardy-weinberg equilibrium . if alleles in the gamete pool exactly mirror those in the parent generation , and if they meet up randomly ( in an infinitely large number of events ) , there is no reason—in fact , no way—for allele and genotype frequencies to change from one generation to the next . in the absence of other factors , you can imagine this process repeating over and over , generation after generation , keeping allele and genotype frequencies the same . since evolution is a change in allele frequencies in a population over generations , a population in hardy-weinberg equilibrium is , by definition , not evolving . but is that realistic ? as we mentioned at the beginning of the article , populations are usually not in hardy-weinberg equilibrium ( at least , not for all of the genes in their genome ) . instead , populations tend to evolve : the allele frequencies of at least some of their genes change from one generation to the next . in fact , population geneticists often check to see if a population is in hardy-weinberg equilibrium because they suspect other forces may be at work . if the population ’ s allele and genotype frequencies are changing over generations ( or if the allele and genotype frequencies do n't match the predictions of the hardy-weinberg equation ) , the race is on to find out why . hardy-weinberg assumptions and evolution what causes populations to evolve ? in order for a population to be in hardy-weinberg equilibrium , or a non-evolving state , it must meet five major assumptions : no mutation . no new alleles are generated by mutation , nor are genes duplicated or deleted . random mating . organisms mate randomly with each other , with no preference for particular genotypes . no gene flow . neither individuals nor their gametes ( e.g. , windborne pollen ) enter or exit the population . very large population size . the population should be effectively infinite in size . no natural selection . all alleles confer equal fitness ( make organisms equally likely to survive and reproduce ) . if any one of these assumptions is not met , the population will not be in hardy-weinberg equilibrium . instead , it may evolve : allele frequencies may change from one generation to the next . allele and genotype frequencies within a single generation may also fail to satisfy the hardy-weinberg equation . some genes may satisfy hardy-weinberg , while others do not note that we can think about hardy-weinberg equilibrium in two ways : for just one gene , or for all the genes in the genome . if we look at just one gene , we check whether the above criteria are true for that one gene . for example , we would ask if there were mutations in that gene , or if organisms mated randomly with regards to their genotype for that gene . if we look at all the genes in the genome , the conditions have to be met for every single gene . while it ’ s possible that the conditions will be more or less met for a single gene under certain circumstances , it ’ s very unlikely that they would be met for all the genes in the genome . so , while a population may be in hardy-weinberg equilibrium for some genes ( not evolving for those genes ) , it ’ s unlikely to be in hardy-weinberg equilibrium for all of its genes ( not evolving at all ) . mechanisms of evolution different hardy-weinberg assumptions , when violated , correspond to different mechanisms of evolution . mutation . although mutation is the original source of all genetic variation , mutation rate for most organisms is pretty low . so , the impact of brand-new mutations on allele frequencies from one generation to the next is usually not large . ( however , natural selection acting on the results of a mutation can be a powerful mechanism of evolution ! ) non-random mating . in non-random mating , organisms may prefer to mate with others of the same genotype or of different genotypes . non-random mating wo n't make allele frequencies in the population change by itself , though it can alter genotype frequencies . this keeps the population from being in hardy-weinberg equilibrium , but it ’ s debatable whether it counts as evolution , since the allele frequencies are staying the same . gene flow . gene flow involves the movement of genes into or out of a population , due to either the movement of individual organisms or their gametes ( eggs and sperm , e.g. , through pollen dispersal by a plant ) . organisms and gametes that enter a population may have new alleles , or may bring in existing alleles but in different proportions than those already in the population . gene flow can be a strong agent of evolution . non-infinite population size ( genetic drift ) . genetic drift involves changes in allele frequency due to chance events – literally , `` sampling error '' in selecting alleles for the next generation . drift can occur in any population of non-infinite size , but it has a stronger effect on small populations . we will look in detail at genetic drift and the effects of population size . natural selection . finally , the most famous mechanism of evolution ! natural selection occurs when one allele ( or combination of alleles of different genes ) makes an organism more or less fit , that is , able to survive and reproduce in a given environment . if an allele reduces fitness , its frequency will tend to drop from one generation to the next . we will look in detail at different forms of natural selection that occur in populations . all five of the above mechanisms of evolution may act to some extent in any natural population . in fact , the evolutionary trajectory of a given gene ( that is , how its alleles change in frequency in the population across generations ) may result from several evolutionary mechanisms acting at once . for instance , one gene ’ s allele frequencies might be modified by both gene flow and genetic drift . for another gene , mutation may produce a new allele , which is then favored ( or disfavored ) by natural selection .
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neither individuals nor their gametes ( e.g. , windborne pollen ) enter or exit the population . very large population size . the population should be effectively infinite in size .
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why is a large population a requirement for hardy-weinberg to work ?
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key points : when a population is in hardy-weinberg equilibrium for a gene , it is not evolving , and allele frequencies will stay the same across generations . there are five basic hardy-weinberg assumptions : no mutation , random mating , no gene flow , infinite population size , and no selection . if the assumptions are not met for a gene , the population may evolve for that gene ( the gene 's allele frequencies may change ) . mechanisms of evolution correspond to violations of different hardy-weinberg assumptions . they are : mutation , non-random mating , gene flow , finite population size ( genetic drift ) , and natural selection . introduction in nature , populations are usually evolving . the grass in an open meadow , the wolves in a forest , and even the bacteria in a person 's body are all natural populations . and all of these populations are likely to be evolving for at least some of their genes . evolution is happing right here , right now ! to be clear , that does n't mean these populations are marching towards some final state of perfection . all evolution means is that a population is changing in its genetic makeup over generations . and the changes may be subtle—for instance , in a wolf population , there might be a shift in the frequency of a gene variant for black rather than gray fur . sometimes , this type of change is due to natural selection . other times , it comes from migration of new organisms into the population , or from random events—the evolutionary `` luck of the draw . '' in this article , we 'll examine what it means for a population evolve , see the ( rarely met ) set of conditions required for a population not to evolve , and explore how failure to meet these conditions does in fact lead to evolution . hardy-weinberg equilibrium first , let 's see what it looks like when a population is not evolving . if a population is in a state called hardy-weinberg equilibrium , the frequencies of alleles , or gene versions , and genotypes , or sets of alleles , in that population will stay the same over generations ( and will also satisfy the hardy-weinberg equation ) . formally , evolution is a change in allele frequencies in a population over time , so a population in hardy-weinberg equilibrium is not evolving . that 's a little bit abstract , so let 's break it down using an example . imagine we have a large population of beetles . in fact , just for the heck of it , let 's say this population is infinitely large . the beetles of our infinitely large population come in two colors , dark gray and light gray , and their color is determined by the a gene . aa and aa beetles are dark gray , and aa beetles are light gray . in our population , let 's say that the a allele has a frequency of $ 0.3 $ , while the a allele has a frequency of $ 0.7 $ . if a population is in hardy-weinberg equilibrium , allele frequencies will be related to genotype frequencies by a specific mathematical relationship , the hardy-weinberg equation . so , we can predict the genotype frequencies we 'd expect to see ( if the population is in hardy-weinberg equilibrium ) by plugging in allele frequencies as shown below : let 's imagine that these are , in fact , the genotype frequencies we see in our beetle population ( $ 9\ % $ aa , $ 42\ % $ aa , $ 49\ % $ aa ) . excellent—our beetles appear to be in hardy-weinberg equilibrium ! now , let 's imagine that the beetles reproduce to make a next generation . what will the allele and genotype frequencies will be in that generation ? to predict this , we need to make a few assumptions : first , let 's assume that none of the genotypes is any better than the others at surviving or getting mates . if this is the case , the frequency of a and a alleles in the pool of gametes ( sperm and eggs ) that meet to make the next generation will be the same as the overall frequency of each allele in the present generation . second , let 's assume that the beetles mate randomly ( as opposed to , say , black beetles preferring other black beetles ) . if this is the case , we can think of reproduction as the result of two random events : selection of a sperm from the population 's gene pool and selection of an egg from the same gene pool . the probability of getting any offspring genotype is just the probability of getting the egg and sperm combo ( s ) that produce that genotype . we can use a modified punnett square to represent the likelihood of getting different offspring genotypes . here , we multiply the frequencies of the gametes on the axes to get the probability of the fertilization events in the squares : as shown above , we 'd predict an offspring generation with the exact same genotype frequencies as the parent generation : $ 9\ % $ aa , $ 42\ % $ aa , and $ 49\ % $ aa . if genotype frequencies have not changed , we also must have the same allele frequencies as in the parent generation : $ 0.3 $ for a and $ 0.7 $ for a . what we 've just seen is the essence of hardy-weinberg equilibrium . if alleles in the gamete pool exactly mirror those in the parent generation , and if they meet up randomly ( in an infinitely large number of events ) , there is no reason—in fact , no way—for allele and genotype frequencies to change from one generation to the next . in the absence of other factors , you can imagine this process repeating over and over , generation after generation , keeping allele and genotype frequencies the same . since evolution is a change in allele frequencies in a population over generations , a population in hardy-weinberg equilibrium is , by definition , not evolving . but is that realistic ? as we mentioned at the beginning of the article , populations are usually not in hardy-weinberg equilibrium ( at least , not for all of the genes in their genome ) . instead , populations tend to evolve : the allele frequencies of at least some of their genes change from one generation to the next . in fact , population geneticists often check to see if a population is in hardy-weinberg equilibrium because they suspect other forces may be at work . if the population ’ s allele and genotype frequencies are changing over generations ( or if the allele and genotype frequencies do n't match the predictions of the hardy-weinberg equation ) , the race is on to find out why . hardy-weinberg assumptions and evolution what causes populations to evolve ? in order for a population to be in hardy-weinberg equilibrium , or a non-evolving state , it must meet five major assumptions : no mutation . no new alleles are generated by mutation , nor are genes duplicated or deleted . random mating . organisms mate randomly with each other , with no preference for particular genotypes . no gene flow . neither individuals nor their gametes ( e.g. , windborne pollen ) enter or exit the population . very large population size . the population should be effectively infinite in size . no natural selection . all alleles confer equal fitness ( make organisms equally likely to survive and reproduce ) . if any one of these assumptions is not met , the population will not be in hardy-weinberg equilibrium . instead , it may evolve : allele frequencies may change from one generation to the next . allele and genotype frequencies within a single generation may also fail to satisfy the hardy-weinberg equation . some genes may satisfy hardy-weinberg , while others do not note that we can think about hardy-weinberg equilibrium in two ways : for just one gene , or for all the genes in the genome . if we look at just one gene , we check whether the above criteria are true for that one gene . for example , we would ask if there were mutations in that gene , or if organisms mated randomly with regards to their genotype for that gene . if we look at all the genes in the genome , the conditions have to be met for every single gene . while it ’ s possible that the conditions will be more or less met for a single gene under certain circumstances , it ’ s very unlikely that they would be met for all the genes in the genome . so , while a population may be in hardy-weinberg equilibrium for some genes ( not evolving for those genes ) , it ’ s unlikely to be in hardy-weinberg equilibrium for all of its genes ( not evolving at all ) . mechanisms of evolution different hardy-weinberg assumptions , when violated , correspond to different mechanisms of evolution . mutation . although mutation is the original source of all genetic variation , mutation rate for most organisms is pretty low . so , the impact of brand-new mutations on allele frequencies from one generation to the next is usually not large . ( however , natural selection acting on the results of a mutation can be a powerful mechanism of evolution ! ) non-random mating . in non-random mating , organisms may prefer to mate with others of the same genotype or of different genotypes . non-random mating wo n't make allele frequencies in the population change by itself , though it can alter genotype frequencies . this keeps the population from being in hardy-weinberg equilibrium , but it ’ s debatable whether it counts as evolution , since the allele frequencies are staying the same . gene flow . gene flow involves the movement of genes into or out of a population , due to either the movement of individual organisms or their gametes ( eggs and sperm , e.g. , through pollen dispersal by a plant ) . organisms and gametes that enter a population may have new alleles , or may bring in existing alleles but in different proportions than those already in the population . gene flow can be a strong agent of evolution . non-infinite population size ( genetic drift ) . genetic drift involves changes in allele frequency due to chance events – literally , `` sampling error '' in selecting alleles for the next generation . drift can occur in any population of non-infinite size , but it has a stronger effect on small populations . we will look in detail at genetic drift and the effects of population size . natural selection . finally , the most famous mechanism of evolution ! natural selection occurs when one allele ( or combination of alleles of different genes ) makes an organism more or less fit , that is , able to survive and reproduce in a given environment . if an allele reduces fitness , its frequency will tend to drop from one generation to the next . we will look in detail at different forms of natural selection that occur in populations . all five of the above mechanisms of evolution may act to some extent in any natural population . in fact , the evolutionary trajectory of a given gene ( that is , how its alleles change in frequency in the population across generations ) may result from several evolutionary mechanisms acting at once . for instance , one gene ’ s allele frequencies might be modified by both gene flow and genetic drift . for another gene , mutation may produce a new allele , which is then favored ( or disfavored ) by natural selection .
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no new alleles are generated by mutation , nor are genes duplicated or deleted . random mating . organisms mate randomly with each other , with no preference for particular genotypes .
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would n't random mating contradict the idea that no net mutations can occur ?
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key points : when a population is in hardy-weinberg equilibrium for a gene , it is not evolving , and allele frequencies will stay the same across generations . there are five basic hardy-weinberg assumptions : no mutation , random mating , no gene flow , infinite population size , and no selection . if the assumptions are not met for a gene , the population may evolve for that gene ( the gene 's allele frequencies may change ) . mechanisms of evolution correspond to violations of different hardy-weinberg assumptions . they are : mutation , non-random mating , gene flow , finite population size ( genetic drift ) , and natural selection . introduction in nature , populations are usually evolving . the grass in an open meadow , the wolves in a forest , and even the bacteria in a person 's body are all natural populations . and all of these populations are likely to be evolving for at least some of their genes . evolution is happing right here , right now ! to be clear , that does n't mean these populations are marching towards some final state of perfection . all evolution means is that a population is changing in its genetic makeup over generations . and the changes may be subtle—for instance , in a wolf population , there might be a shift in the frequency of a gene variant for black rather than gray fur . sometimes , this type of change is due to natural selection . other times , it comes from migration of new organisms into the population , or from random events—the evolutionary `` luck of the draw . '' in this article , we 'll examine what it means for a population evolve , see the ( rarely met ) set of conditions required for a population not to evolve , and explore how failure to meet these conditions does in fact lead to evolution . hardy-weinberg equilibrium first , let 's see what it looks like when a population is not evolving . if a population is in a state called hardy-weinberg equilibrium , the frequencies of alleles , or gene versions , and genotypes , or sets of alleles , in that population will stay the same over generations ( and will also satisfy the hardy-weinberg equation ) . formally , evolution is a change in allele frequencies in a population over time , so a population in hardy-weinberg equilibrium is not evolving . that 's a little bit abstract , so let 's break it down using an example . imagine we have a large population of beetles . in fact , just for the heck of it , let 's say this population is infinitely large . the beetles of our infinitely large population come in two colors , dark gray and light gray , and their color is determined by the a gene . aa and aa beetles are dark gray , and aa beetles are light gray . in our population , let 's say that the a allele has a frequency of $ 0.3 $ , while the a allele has a frequency of $ 0.7 $ . if a population is in hardy-weinberg equilibrium , allele frequencies will be related to genotype frequencies by a specific mathematical relationship , the hardy-weinberg equation . so , we can predict the genotype frequencies we 'd expect to see ( if the population is in hardy-weinberg equilibrium ) by plugging in allele frequencies as shown below : let 's imagine that these are , in fact , the genotype frequencies we see in our beetle population ( $ 9\ % $ aa , $ 42\ % $ aa , $ 49\ % $ aa ) . excellent—our beetles appear to be in hardy-weinberg equilibrium ! now , let 's imagine that the beetles reproduce to make a next generation . what will the allele and genotype frequencies will be in that generation ? to predict this , we need to make a few assumptions : first , let 's assume that none of the genotypes is any better than the others at surviving or getting mates . if this is the case , the frequency of a and a alleles in the pool of gametes ( sperm and eggs ) that meet to make the next generation will be the same as the overall frequency of each allele in the present generation . second , let 's assume that the beetles mate randomly ( as opposed to , say , black beetles preferring other black beetles ) . if this is the case , we can think of reproduction as the result of two random events : selection of a sperm from the population 's gene pool and selection of an egg from the same gene pool . the probability of getting any offspring genotype is just the probability of getting the egg and sperm combo ( s ) that produce that genotype . we can use a modified punnett square to represent the likelihood of getting different offspring genotypes . here , we multiply the frequencies of the gametes on the axes to get the probability of the fertilization events in the squares : as shown above , we 'd predict an offspring generation with the exact same genotype frequencies as the parent generation : $ 9\ % $ aa , $ 42\ % $ aa , and $ 49\ % $ aa . if genotype frequencies have not changed , we also must have the same allele frequencies as in the parent generation : $ 0.3 $ for a and $ 0.7 $ for a . what we 've just seen is the essence of hardy-weinberg equilibrium . if alleles in the gamete pool exactly mirror those in the parent generation , and if they meet up randomly ( in an infinitely large number of events ) , there is no reason—in fact , no way—for allele and genotype frequencies to change from one generation to the next . in the absence of other factors , you can imagine this process repeating over and over , generation after generation , keeping allele and genotype frequencies the same . since evolution is a change in allele frequencies in a population over generations , a population in hardy-weinberg equilibrium is , by definition , not evolving . but is that realistic ? as we mentioned at the beginning of the article , populations are usually not in hardy-weinberg equilibrium ( at least , not for all of the genes in their genome ) . instead , populations tend to evolve : the allele frequencies of at least some of their genes change from one generation to the next . in fact , population geneticists often check to see if a population is in hardy-weinberg equilibrium because they suspect other forces may be at work . if the population ’ s allele and genotype frequencies are changing over generations ( or if the allele and genotype frequencies do n't match the predictions of the hardy-weinberg equation ) , the race is on to find out why . hardy-weinberg assumptions and evolution what causes populations to evolve ? in order for a population to be in hardy-weinberg equilibrium , or a non-evolving state , it must meet five major assumptions : no mutation . no new alleles are generated by mutation , nor are genes duplicated or deleted . random mating . organisms mate randomly with each other , with no preference for particular genotypes . no gene flow . neither individuals nor their gametes ( e.g. , windborne pollen ) enter or exit the population . very large population size . the population should be effectively infinite in size . no natural selection . all alleles confer equal fitness ( make organisms equally likely to survive and reproduce ) . if any one of these assumptions is not met , the population will not be in hardy-weinberg equilibrium . instead , it may evolve : allele frequencies may change from one generation to the next . allele and genotype frequencies within a single generation may also fail to satisfy the hardy-weinberg equation . some genes may satisfy hardy-weinberg , while others do not note that we can think about hardy-weinberg equilibrium in two ways : for just one gene , or for all the genes in the genome . if we look at just one gene , we check whether the above criteria are true for that one gene . for example , we would ask if there were mutations in that gene , or if organisms mated randomly with regards to their genotype for that gene . if we look at all the genes in the genome , the conditions have to be met for every single gene . while it ’ s possible that the conditions will be more or less met for a single gene under certain circumstances , it ’ s very unlikely that they would be met for all the genes in the genome . so , while a population may be in hardy-weinberg equilibrium for some genes ( not evolving for those genes ) , it ’ s unlikely to be in hardy-weinberg equilibrium for all of its genes ( not evolving at all ) . mechanisms of evolution different hardy-weinberg assumptions , when violated , correspond to different mechanisms of evolution . mutation . although mutation is the original source of all genetic variation , mutation rate for most organisms is pretty low . so , the impact of brand-new mutations on allele frequencies from one generation to the next is usually not large . ( however , natural selection acting on the results of a mutation can be a powerful mechanism of evolution ! ) non-random mating . in non-random mating , organisms may prefer to mate with others of the same genotype or of different genotypes . non-random mating wo n't make allele frequencies in the population change by itself , though it can alter genotype frequencies . this keeps the population from being in hardy-weinberg equilibrium , but it ’ s debatable whether it counts as evolution , since the allele frequencies are staying the same . gene flow . gene flow involves the movement of genes into or out of a population , due to either the movement of individual organisms or their gametes ( eggs and sperm , e.g. , through pollen dispersal by a plant ) . organisms and gametes that enter a population may have new alleles , or may bring in existing alleles but in different proportions than those already in the population . gene flow can be a strong agent of evolution . non-infinite population size ( genetic drift ) . genetic drift involves changes in allele frequency due to chance events – literally , `` sampling error '' in selecting alleles for the next generation . drift can occur in any population of non-infinite size , but it has a stronger effect on small populations . we will look in detail at genetic drift and the effects of population size . natural selection . finally , the most famous mechanism of evolution ! natural selection occurs when one allele ( or combination of alleles of different genes ) makes an organism more or less fit , that is , able to survive and reproduce in a given environment . if an allele reduces fitness , its frequency will tend to drop from one generation to the next . we will look in detail at different forms of natural selection that occur in populations . all five of the above mechanisms of evolution may act to some extent in any natural population . in fact , the evolutionary trajectory of a given gene ( that is , how its alleles change in frequency in the population across generations ) may result from several evolutionary mechanisms acting at once . for instance , one gene ’ s allele frequencies might be modified by both gene flow and genetic drift . for another gene , mutation may produce a new allele , which is then favored ( or disfavored ) by natural selection .
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no new alleles are generated by mutation , nor are genes duplicated or deleted . random mating . organisms mate randomly with each other , with no preference for particular genotypes .
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if random mating does happen , would n't it increase the chances of a mutation ?
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invitations to visit europe by the time the 1770s arrived , john singleton copley was the undisputed king of portraiture in the american colonies . yet despite this fact , he had longed to visit the old world , and he had , in fact , received much encouragement to permanently move to london . copley ’ s early masterwork boy with a squirrel , a portrait of his half brother henry pelham , had been shown at the 1766 society of artists exhibition . many artists , particularly benjamin west and sir joshua reynolds , had been suitably impressed with the artistic virtuosity of the new world wunderkind . west , himself a colonial , wrote to copley on 4 august 1766 to encourage him embark on a grand tour of europe . with his creative spelling , west urged copley to make a “ viset to europe for this porpase for three or four years , you would find yourself then in possession of what will be highly valuable '' ( this and all quotes use the 18th century spelling ) . copley , ever the prudent businessman , was seldom rash or spontaneous . although west provided rather constant motivation , copley remained unconvinced that he would have a more affluent life in london than the one he then had in boston . on 17 june 1768 , for example , copley wrote to the west that , “ i should be glad to go to europe , but can not think of it without a very good prospect of doing as well there as i can here . you are sensable that 300 guineas a year , which is my present income , is a pretty living in america. ” copley continued in this letter to make it clear that he had family obligations to consider : “ and what ever my ambition may be to excel in our noble art , i can not think of doing it at the expence of not only my own happyness , but that of a tender mother and a young brother whose dependance is intirely upon me. ” several years later—in january 1772—john trumbull , the future painter of the declaration of independence , was travelling from his home in connecticut to cambridge , massachusetts in order to enroll at harvard college . although trumbull wanted to be an artist , his father , the former governor of connecticut , wished for his son to receive a college education and to pursue a more socially prestigious vocation . although trumbull was unenthusiastic about the prospect of being a college student , he was excited about visiting copley , an encounter made possible through a mutual friend . writing his autobiography nearly fifty years later , trumbull still recalled this first brush—get it ? brush ! —with artistic fame : we found mr. copley dressed to receive a party of friends at dinner . i remember his dress and appearance—an elegant looking man , dressed in a fine maroon cloth , with gilt buttons—this was dazzling to my unpracticed eye ! —but his paintings , the first i had ever seen deserving the name , riveted , absorbed my attention , and renewed all my desire to enter upon such a pursuit . copley leaves for london ( as political tensions rise ) and goes on the grand tour in a city—boston—that was becoming increasingly more divided between the tories and the whigs ( those who preferred loyalty to britain and those who wished for independence , respectively ) , copley remained as apolitical as he could . indeed , a look at his boston patronage indicates that he painted sitters on both sides of the growing vitriolic political divide . but as the 1770s progressed , copley ’ s life became more and more uncomfortable . most of his wife ’ s family were strident loyalists . his father-in-law richard clarke , for example , was the owner of the tea that provoked the boston tea party on 16 december 1773 . several months later—april of 1774—an angry mob arrived at copley ’ s home looking for colonel george watson , a tory lawyer copley had painted in 1768 . this unruly event frightened copley and helped him realize that the political climate was beginning to get out of hand . “ what a spirit ! ” copley wrote on 26 april . “ what if mr. watson had stayed ( as i pressed him to ) to spend the night . i must either have given up a friend to the insult of a mob or had my house pulled down and perhaps my family murthered. ” fearful for his own safety , copley sailed for london in june 1774 , just seven weeks later . his family—wife , children , mother , and half-brothers—remained in boston . copley ’ s passage across the atlantic lasted until the second week of july , and he wasted little time in visiting benjamin west , joshua reynolds , and the royal academy of art . after some time in london , copley began his continental grand tour , an eighteenth-century staple of art education for an aspiring painter . he first visited paris—writing to his wife on 2 september—then made his way to rome via genoa . copley arrived in rome on 26 october and spent the next seven months viewing art and architecture and copying the old masters . he also made several side trips to naples , pompeii , herculaneum , and paestum . a letter copley wrote to his mother from parma on 25 june 1775 states that he had finally left rome for london on 4 june 1775 ; he had already visited florence on his way north . still in parma on 22 august , copley wrote a lengthy letter to his half-brother and stated that , “ i propose going from this [ parma ] to venice and through the tirole , germany , and flanders , which is the shortest way to england and a different rout from that i took in coming to italy . i shall not return to parris as i intended. ” in just fifteen months—that is from his departure from boston to his return to london from the continent in october 1775—copley had received nothing short of an art education unavailable to anyone in north america . he was primed to open a painting studio in london . by the time he returned to london , his wife and three of their ( then ) four children were awaiting his return ( the youngest , clarke copley , born in 1775 , did not travel with the rest of the family and died the following year ) . copley thusly flipped the page to a new chapter—the english chapter—in his professional life . copley painted an immense group portrait , the copley family , in order to celebrate—and announce—this new chapter in his professional development . this painting accomplished several independent goals at the same time . to begin , it serves as a kind of visual testament to his love and devotion to his family . during their nearly 15 months apart , copley ’ s correspondence—primarily to his own mother , his half-brother henry , and his wife suzanna who he affectionately referred to as sukey—is filled with references to both missing his family and his fear for their safety in the increasingly tenuous city of boston . writing from lyon on 15-16 september 1774 , for example , copley stated , “ i am very ancious for you , my dear , and our children , for i know not what state you are in , in boston ; but i pray god to preserve you and them. ” in closing , he sends affectionate tidings : “ give my blessing to my dear babys , and a thousand kisses . tell my dear betsey not to forget he [ r ] papa. ” the copley family shows the six members of the artist ’ s clan as it existed at the beginning of 1777 . copley has shown three adults—the artist , his wife , and her father—and his four children . as was typical with group portraits that included a self-portrait—see raphael in the school of athens and smibert ’ s self representation in the bermuda group , both of which copley would have seen—the artist looks directly at the viewer , a look of inquisitiveness on his visage . he holds a set of drawings and leans on a classical plinth . his father-in-law , richard clarke , looks to the viewer ’ s right , seemingly unaware that the youngest daughter , susanna , is attempting to climb onto his lap . sukey , shown in profile , lovingly nuzzles john singleton , jr. , their only son , while mary , on the far right , attempts to capture her mother ’ s attention . the only other sitter who seems alerted to the viewer is the oldest , elizabeth , who stands seemingly unaware of the happenings behind her . although clarke seems more aloof than loving , the rest of the participants in this stage-like setting seem to express tenderness and love for one another . children play and vie for motherly affection . sukey plays the maternal role of a loving and tender parent . elizabeth , the oldest , suspiciously stares at the viewer as if facing a stranger . copley demonstrates—as he had so consistently in boston—a keen ability to paint psychologically rich and complex compositions . these are not only accurate likenesses of those who he most loved . indeed , copley is able to tell us , through visual means , a bit about who they are . however , this portrait was not only intended to accurately record who the copley family was and what the copley family looked like at a particular moment in time . instead , copley completed this work as a way of both advertising his talents and abilities as a painter , but also to announce his family ’ s formal arrival into fashionable london society . copley and his wife wear clothing then at the height of fashion , and this attire , in addition to the drapery on the left of the painting and the extravagant furniture and beautifully rendered carpet , dually speaks to the artist ’ s affluent wealth and his ability at painting fabrics . the drawing he holds , the vase behind his hands—identified as a copy of the medici vase copley would have seen in the uffizi while in florence—and the italianate landscape in the distance that appears as if borrowed from a raphael madonna and child painting all proclaim his grand tour pedigree . available for hire in size ( 6 ’ x 7.5 ’ ) , composition , and in artistic references , copley intended for this group portrait to eloquently advertise that his newly arrived services were available for hire to the london portrait-seeking public . copley exhibited this work at the 1777 royal academy show to nearly universal acclaim . in a career that would extend for almost another forty years , this painting is the only one he formally exhibited with his own likeness within it . clearly , the work is not only about what it is , but also who made it . the artist achieved his goal . one critic remarked , “ mr . copley , from the size of his family piece , is likely to be as much the subject of observation in the rooms as any artist who has exhibited… ” years later , in 1792 , copley had achieved such fame that he was set to rival his former advocate , benjamin west , for the presidency of the royal academy of art . between the copley family in 1777 and the end of his career , the artist shifted his attention from portraiture—which had been his only focus in the american colonies—to that of the more prestigious and ambitious history paintings . essay by dr. bryan zygmont additional resources : this painting at the national gallery of art copley at the national gallery of art john smibert 's the bermuda group at yale university art gallery copley on the metropolitan museum of art 's heilbrunn timeline of art history portrait painting in england on the metropolitan museum of art 's heilbrunn timeline of art history
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writing his autobiography nearly fifty years later , trumbull still recalled this first brush—get it ? brush ! —with artistic fame : we found mr. copley dressed to receive a party of friends at dinner . i remember his dress and appearance—an elegant looking man , dressed in a fine maroon cloth , with gilt buttons—this was dazzling to my unpracticed eye !
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what was the artistic fight copley made against the british ?
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half . if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 . once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern . every time we double the size of the array , we need at most one more guess . suppose we need at most $ m $ guesses for an array of length $ n $ . then , for an array of length $ 2n $ , the first guess cuts the reasonable portion of the array down to size $ n $ , and at most $ m $ guesses finish up , giving us a total of at most $ m+1 $ guesses . let 's look at the general case of an array of length $ n $ . we can express the number of guesses , in the worst case , as `` the number of times we can repeatedly halve , starting at $ n $ , until we get the value 1 , plus one . '' but that 's inconvenient to write out . fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ . when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search ! compare them below : in the next tutorial , we 'll see how computer scientists characterize the running times of linear search and binary search , using a notation that distills the most important part of the running time and discards the less important parts . this content is a collaboration of dartmouth computer science professors thomas cormen and devin balkcom , plus the khan academy computing curriculum team . the content is licensed cc-by-nc-sa .
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fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . )
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the last graph shows n versus n lg n. should n't it just be lg n ?
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half . if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 . once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern . every time we double the size of the array , we need at most one more guess . suppose we need at most $ m $ guesses for an array of length $ n $ . then , for an array of length $ 2n $ , the first guess cuts the reasonable portion of the array down to size $ n $ , and at most $ m $ guesses finish up , giving us a total of at most $ m+1 $ guesses . let 's look at the general case of an array of length $ n $ . we can express the number of guesses , in the worst case , as `` the number of times we can repeatedly halve , starting at $ n $ , until we get the value 1 , plus one . '' but that 's inconvenient to write out . fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ . when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search ! compare them below : in the next tutorial , we 'll see how computer scientists characterize the running times of linear search and binary search , using a notation that distills the most important part of the running time and discards the less important parts . this content is a collaboration of dartmouth computer science professors thomas cormen and devin balkcom , plus the khan academy computing curriculum team . the content is licensed cc-by-nc-sa .
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therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search !
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how do i calculate base-2 logarithms of a number on a calculator ?
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half . if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 . once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern . every time we double the size of the array , we need at most one more guess . suppose we need at most $ m $ guesses for an array of length $ n $ . then , for an array of length $ 2n $ , the first guess cuts the reasonable portion of the array down to size $ n $ , and at most $ m $ guesses finish up , giving us a total of at most $ m+1 $ guesses . let 's look at the general case of an array of length $ n $ . we can express the number of guesses , in the worst case , as `` the number of times we can repeatedly halve , starting at $ n $ , until we get the value 1 , plus one . '' but that 's inconvenient to write out . fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ . when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search ! compare them below : in the next tutorial , we 'll see how computer scientists characterize the running times of linear search and binary search , using a notation that distills the most important part of the running time and discards the less important parts . this content is a collaboration of dartmouth computer science professors thomas cormen and devin balkcom , plus the khan academy computing curriculum team . the content is licensed cc-by-nc-sa .
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases .
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why is it called binary search if there are three options ?
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half . if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 . once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern . every time we double the size of the array , we need at most one more guess . suppose we need at most $ m $ guesses for an array of length $ n $ . then , for an array of length $ 2n $ , the first guess cuts the reasonable portion of the array down to size $ n $ , and at most $ m $ guesses finish up , giving us a total of at most $ m+1 $ guesses . let 's look at the general case of an array of length $ n $ . we can express the number of guesses , in the worst case , as `` the number of times we can repeatedly halve , starting at $ n $ , until we get the value 1 , plus one . '' but that 's inconvenient to write out . fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ . when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search ! compare them below : in the next tutorial , we 'll see how computer scientists characterize the running times of linear search and binary search , using a notation that distills the most important part of the running time and discards the less important parts . this content is a collaboration of dartmouth computer science professors thomas cormen and devin balkcom , plus the khan academy computing curriculum team . the content is licensed cc-by-nc-sa .
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for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses .
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on the last challenge how would i complete step 3 and print how many guesses the computer used ?
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half . if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 . once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern . every time we double the size of the array , we need at most one more guess . suppose we need at most $ m $ guesses for an array of length $ n $ . then , for an array of length $ 2n $ , the first guess cuts the reasonable portion of the array down to size $ n $ , and at most $ m $ guesses finish up , giving us a total of at most $ m+1 $ guesses . let 's look at the general case of an array of length $ n $ . we can express the number of guesses , in the worst case , as `` the number of times we can repeatedly halve , starting at $ n $ , until we get the value 1 , plus one . '' but that 's inconvenient to write out . fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ . when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search ! compare them below : in the next tutorial , we 'll see how computer scientists characterize the running times of linear search and binary search , using a notation that distills the most important part of the running time and discards the less important parts . this content is a collaboration of dartmouth computer science professors thomas cormen and devin balkcom , plus the khan academy computing curriculum team . the content is licensed cc-by-nc-sa .
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search .
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why is n't there an option to chose what programming language you want to use ?
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half . if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 . once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern . every time we double the size of the array , we need at most one more guess . suppose we need at most $ m $ guesses for an array of length $ n $ . then , for an array of length $ 2n $ , the first guess cuts the reasonable portion of the array down to size $ n $ , and at most $ m $ guesses finish up , giving us a total of at most $ m+1 $ guesses . let 's look at the general case of an array of length $ n $ . we can express the number of guesses , in the worst case , as `` the number of times we can repeatedly halve , starting at $ n $ , until we get the value 1 , plus one . '' but that 's inconvenient to write out . fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ . when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search ! compare them below : in the next tutorial , we 'll see how computer scientists characterize the running times of linear search and binary search , using a notation that distills the most important part of the running time and discards the less important parts . this content is a collaboration of dartmouth computer science professors thomas cormen and devin balkcom , plus the khan academy computing curriculum team . the content is licensed cc-by-nc-sa .
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases .
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what types of algorithms does google use for their search engine ?
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half . if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 . once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern . every time we double the size of the array , we need at most one more guess . suppose we need at most $ m $ guesses for an array of length $ n $ . then , for an array of length $ 2n $ , the first guess cuts the reasonable portion of the array down to size $ n $ , and at most $ m $ guesses finish up , giving us a total of at most $ m+1 $ guesses . let 's look at the general case of an array of length $ n $ . we can express the number of guesses , in the worst case , as `` the number of times we can repeatedly halve , starting at $ n $ , until we get the value 1 , plus one . '' but that 's inconvenient to write out . fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ . when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search ! compare them below : in the next tutorial , we 'll see how computer scientists characterize the running times of linear search and binary search , using a notation that distills the most important part of the running time and discards the less important parts . this content is a collaboration of dartmouth computer science professors thomas cormen and devin balkcom , plus the khan academy computing curriculum team . the content is licensed cc-by-nc-sa .
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases .
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in the binary search challenge why in the third step the println function has to be added in the if loop and not outside the if else statements ?
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half . if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 . once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern . every time we double the size of the array , we need at most one more guess . suppose we need at most $ m $ guesses for an array of length $ n $ . then , for an array of length $ 2n $ , the first guess cuts the reasonable portion of the array down to size $ n $ , and at most $ m $ guesses finish up , giving us a total of at most $ m+1 $ guesses . let 's look at the general case of an array of length $ n $ . we can express the number of guesses , in the worst case , as `` the number of times we can repeatedly halve , starting at $ n $ , until we get the value 1 , plus one . '' but that 's inconvenient to write out . fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ . when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search ! compare them below : in the next tutorial , we 'll see how computer scientists characterize the running times of linear search and binary search , using a notation that distills the most important part of the running time and discards the less important parts . this content is a collaboration of dartmouth computer science professors thomas cormen and devin balkcom , plus the khan academy computing curriculum team . the content is licensed cc-by-nc-sa .
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search .
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if n=3 , the maximum guesses are 3 ?
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half . if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 . once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern . every time we double the size of the array , we need at most one more guess . suppose we need at most $ m $ guesses for an array of length $ n $ . then , for an array of length $ 2n $ , the first guess cuts the reasonable portion of the array down to size $ n $ , and at most $ m $ guesses finish up , giving us a total of at most $ m+1 $ guesses . let 's look at the general case of an array of length $ n $ . we can express the number of guesses , in the worst case , as `` the number of times we can repeatedly halve , starting at $ n $ , until we get the value 1 , plus one . '' but that 's inconvenient to write out . fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ . when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search ! compare them below : in the next tutorial , we 'll see how computer scientists characterize the running times of linear search and binary search , using a notation that distills the most important part of the running time and discards the less important parts . this content is a collaboration of dartmouth computer science professors thomas cormen and devin balkcom , plus the khan academy computing curriculum team . the content is licensed cc-by-nc-sa .
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( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ .
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from this , are we then concluding that the running time of a binary search is ( ( log n ) + 1 ) to base 2 where n is the length of the array ?
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half . if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 . once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern . every time we double the size of the array , we need at most one more guess . suppose we need at most $ m $ guesses for an array of length $ n $ . then , for an array of length $ 2n $ , the first guess cuts the reasonable portion of the array down to size $ n $ , and at most $ m $ guesses finish up , giving us a total of at most $ m+1 $ guesses . let 's look at the general case of an array of length $ n $ . we can express the number of guesses , in the worst case , as `` the number of times we can repeatedly halve , starting at $ n $ , until we get the value 1 , plus one . '' but that 's inconvenient to write out . fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ . when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search ! compare them below : in the next tutorial , we 'll see how computer scientists characterize the running times of linear search and binary search , using a notation that distills the most important part of the running time and discards the less important parts . this content is a collaboration of dartmouth computer science professors thomas cormen and devin balkcom , plus the khan academy computing curriculum team . the content is licensed cc-by-nc-sa .
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( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ .
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is it correct to say that ln ( n ) is faster than n*ln ( n ) , since it 's the last is equal to 2^ ( x/y ) ?
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half . if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 . once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern . every time we double the size of the array , we need at most one more guess . suppose we need at most $ m $ guesses for an array of length $ n $ . then , for an array of length $ 2n $ , the first guess cuts the reasonable portion of the array down to size $ n $ , and at most $ m $ guesses finish up , giving us a total of at most $ m+1 $ guesses . let 's look at the general case of an array of length $ n $ . we can express the number of guesses , in the worst case , as `` the number of times we can repeatedly halve , starting at $ n $ , until we get the value 1 , plus one . '' but that 's inconvenient to write out . fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ . when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search ! compare them below : in the next tutorial , we 'll see how computer scientists characterize the running times of linear search and binary search , using a notation that distills the most important part of the running time and discards the less important parts . this content is a collaboration of dartmouth computer science professors thomas cormen and devin balkcom , plus the khan academy computing curriculum team . the content is licensed cc-by-nc-sa .
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when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses .
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not sure why it is not just 2^ ( 10+1 ) which is 2^11 instead of 11 ( 10+1 ) ?
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half . if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 . once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern . every time we double the size of the array , we need at most one more guess . suppose we need at most $ m $ guesses for an array of length $ n $ . then , for an array of length $ 2n $ , the first guess cuts the reasonable portion of the array down to size $ n $ , and at most $ m $ guesses finish up , giving us a total of at most $ m+1 $ guesses . let 's look at the general case of an array of length $ n $ . we can express the number of guesses , in the worst case , as `` the number of times we can repeatedly halve , starting at $ n $ , until we get the value 1 , plus one . '' but that 's inconvenient to write out . fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ . when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search ! compare them below : in the next tutorial , we 'll see how computer scientists characterize the running times of linear search and binary search , using a notation that distills the most important part of the running time and discards the less important parts . this content is a collaboration of dartmouth computer science professors thomas cormen and devin balkcom , plus the khan academy computing curriculum team . the content is licensed cc-by-nc-sa .
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for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses .
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why are we multiplying 11 by 11 ?
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half . if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 . once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern . every time we double the size of the array , we need at most one more guess . suppose we need at most $ m $ guesses for an array of length $ n $ . then , for an array of length $ 2n $ , the first guess cuts the reasonable portion of the array down to size $ n $ , and at most $ m $ guesses finish up , giving us a total of at most $ m+1 $ guesses . let 's look at the general case of an array of length $ n $ . we can express the number of guesses , in the worst case , as `` the number of times we can repeatedly halve , starting at $ n $ , until we get the value 1 , plus one . '' but that 's inconvenient to write out . fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ . when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search ! compare them below : in the next tutorial , we 'll see how computer scientists characterize the running times of linear search and binary search , using a notation that distills the most important part of the running time and discards the less important parts . this content is a collaboration of dartmouth computer science professors thomas cormen and devin balkcom , plus the khan academy computing curriculum team . the content is licensed cc-by-nc-sa .
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once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ?
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in an array of length 8 , how is it that we need four guesses ?
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half . if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 . once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern . every time we double the size of the array , we need at most one more guess . suppose we need at most $ m $ guesses for an array of length $ n $ . then , for an array of length $ 2n $ , the first guess cuts the reasonable portion of the array down to size $ n $ , and at most $ m $ guesses finish up , giving us a total of at most $ m+1 $ guesses . let 's look at the general case of an array of length $ n $ . we can express the number of guesses , in the worst case , as `` the number of times we can repeatedly halve , starting at $ n $ , until we get the value 1 , plus one . '' but that 's inconvenient to write out . fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ . when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search ! compare them below : in the next tutorial , we 'll see how computer scientists characterize the running times of linear search and binary search , using a notation that distills the most important part of the running time and discards the less important parts . this content is a collaboration of dartmouth computer science professors thomas cormen and devin balkcom , plus the khan academy computing curriculum team . the content is licensed cc-by-nc-sa .
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you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes .
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what is the worst case ?
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half . if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 . once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern . every time we double the size of the array , we need at most one more guess . suppose we need at most $ m $ guesses for an array of length $ n $ . then , for an array of length $ 2n $ , the first guess cuts the reasonable portion of the array down to size $ n $ , and at most $ m $ guesses finish up , giving us a total of at most $ m+1 $ guesses . let 's look at the general case of an array of length $ n $ . we can express the number of guesses , in the worst case , as `` the number of times we can repeatedly halve , starting at $ n $ , until we get the value 1 , plus one . '' but that 's inconvenient to write out . fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ . when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search ! compare them below : in the next tutorial , we 'll see how computer scientists characterize the running times of linear search and binary search , using a notation that distills the most important part of the running time and discards the less important parts . this content is a collaboration of dartmouth computer science professors thomas cormen and devin balkcom , plus the khan academy computing curriculum team . the content is licensed cc-by-nc-sa .
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search .
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what is n in that graph ?
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half . if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 . once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern . every time we double the size of the array , we need at most one more guess . suppose we need at most $ m $ guesses for an array of length $ n $ . then , for an array of length $ 2n $ , the first guess cuts the reasonable portion of the array down to size $ n $ , and at most $ m $ guesses finish up , giving us a total of at most $ m+1 $ guesses . let 's look at the general case of an array of length $ n $ . we can express the number of guesses , in the worst case , as `` the number of times we can repeatedly halve , starting at $ n $ , until we get the value 1 , plus one . '' but that 's inconvenient to write out . fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ . when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search ! compare them below : in the next tutorial , we 'll see how computer scientists characterize the running times of linear search and binary search , using a notation that distills the most important part of the running time and discards the less important parts . this content is a collaboration of dartmouth computer science professors thomas cormen and devin balkcom , plus the khan academy computing curriculum team . the content is licensed cc-by-nc-sa .
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what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses .
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i keep getting : `` hm , how are you calculating the new midpoint index ?
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half . if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 . once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern . every time we double the size of the array , we need at most one more guess . suppose we need at most $ m $ guesses for an array of length $ n $ . then , for an array of length $ 2n $ , the first guess cuts the reasonable portion of the array down to size $ n $ , and at most $ m $ guesses finish up , giving us a total of at most $ m+1 $ guesses . let 's look at the general case of an array of length $ n $ . we can express the number of guesses , in the worst case , as `` the number of times we can repeatedly halve , starting at $ n $ , until we get the value 1 , plus one . '' but that 's inconvenient to write out . fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ . when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search ! compare them below : in the next tutorial , we 'll see how computer scientists characterize the running times of linear search and binary search , using a notation that distills the most important part of the running time and discards the less important parts . this content is a collaboration of dartmouth computer science professors thomas cormen and devin balkcom , plus the khan academy computing curriculum team . the content is licensed cc-by-nc-sa .
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fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . )
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is there any difference between lg and log ?
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half . if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 . once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern . every time we double the size of the array , we need at most one more guess . suppose we need at most $ m $ guesses for an array of length $ n $ . then , for an array of length $ 2n $ , the first guess cuts the reasonable portion of the array down to size $ n $ , and at most $ m $ guesses finish up , giving us a total of at most $ m+1 $ guesses . let 's look at the general case of an array of length $ n $ . we can express the number of guesses , in the worst case , as `` the number of times we can repeatedly halve , starting at $ n $ , until we get the value 1 , plus one . '' but that 's inconvenient to write out . fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ . when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search ! compare them below : in the next tutorial , we 'll see how computer scientists characterize the running times of linear search and binary search , using a notation that distills the most important part of the running time and discards the less important parts . this content is a collaboration of dartmouth computer science professors thomas cormen and devin balkcom , plus the khan academy computing curriculum team . the content is licensed cc-by-nc-sa .
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for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses .
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can someone please explain in detail how they came up with the following expression : 11 * ( 10+1 ) ?
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half . if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 . once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern . every time we double the size of the array , we need at most one more guess . suppose we need at most $ m $ guesses for an array of length $ n $ . then , for an array of length $ 2n $ , the first guess cuts the reasonable portion of the array down to size $ n $ , and at most $ m $ guesses finish up , giving us a total of at most $ m+1 $ guesses . let 's look at the general case of an array of length $ n $ . we can express the number of guesses , in the worst case , as `` the number of times we can repeatedly halve , starting at $ n $ , until we get the value 1 , plus one . '' but that 's inconvenient to write out . fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ . when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search ! compare them below : in the next tutorial , we 'll see how computer scientists characterize the running times of linear search and binary search , using a notation that distills the most important part of the running time and discards the less important parts . this content is a collaboration of dartmouth computer science professors thomas cormen and devin balkcom , plus the khan academy computing curriculum team . the content is licensed cc-by-nc-sa .
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases .
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in the case of binary search , which is faster than o ( n ) linear search , should it just be o ( lg n ) ?
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half . if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 . once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern . every time we double the size of the array , we need at most one more guess . suppose we need at most $ m $ guesses for an array of length $ n $ . then , for an array of length $ 2n $ , the first guess cuts the reasonable portion of the array down to size $ n $ , and at most $ m $ guesses finish up , giving us a total of at most $ m+1 $ guesses . let 's look at the general case of an array of length $ n $ . we can express the number of guesses , in the worst case , as `` the number of times we can repeatedly halve , starting at $ n $ , until we get the value 1 , plus one . '' but that 's inconvenient to write out . fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ . when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search ! compare them below : in the next tutorial , we 'll see how computer scientists characterize the running times of linear search and binary search , using a notation that distills the most important part of the running time and discards the less important parts . this content is a collaboration of dartmouth computer science professors thomas cormen and devin balkcom , plus the khan academy computing curriculum team . the content is licensed cc-by-nc-sa .
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fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . )
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the last graph shows n versus n lg n. should n't it just be lg n ?
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half . if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 . once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern . every time we double the size of the array , we need at most one more guess . suppose we need at most $ m $ guesses for an array of length $ n $ . then , for an array of length $ 2n $ , the first guess cuts the reasonable portion of the array down to size $ n $ , and at most $ m $ guesses finish up , giving us a total of at most $ m+1 $ guesses . let 's look at the general case of an array of length $ n $ . we can express the number of guesses , in the worst case , as `` the number of times we can repeatedly halve , starting at $ n $ , until we get the value 1 , plus one . '' but that 's inconvenient to write out . fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ . when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search ! compare them below : in the next tutorial , we 'll see how computer scientists characterize the running times of linear search and binary search , using a notation that distills the most important part of the running time and discards the less important parts . this content is a collaboration of dartmouth computer science professors thomas cormen and devin balkcom , plus the khan academy computing curriculum team . the content is licensed cc-by-nc-sa .
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if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern .
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i need help , does anyone know what i need to put in the 'while loop ' and how to stop it ?
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half . if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 . once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern . every time we double the size of the array , we need at most one more guess . suppose we need at most $ m $ guesses for an array of length $ n $ . then , for an array of length $ 2n $ , the first guess cuts the reasonable portion of the array down to size $ n $ , and at most $ m $ guesses finish up , giving us a total of at most $ m+1 $ guesses . let 's look at the general case of an array of length $ n $ . we can express the number of guesses , in the worst case , as `` the number of times we can repeatedly halve , starting at $ n $ , until we get the value 1 , plus one . '' but that 's inconvenient to write out . fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ . when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search ! compare them below : in the next tutorial , we 'll see how computer scientists characterize the running times of linear search and binary search , using a notation that distills the most important part of the running time and discards the less important parts . this content is a collaboration of dartmouth computer science professors thomas cormen and devin balkcom , plus the khan academy computing curriculum team . the content is licensed cc-by-nc-sa .
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half .
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what is the average number of guesses for a binary search ?
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half . if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 . once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern . every time we double the size of the array , we need at most one more guess . suppose we need at most $ m $ guesses for an array of length $ n $ . then , for an array of length $ 2n $ , the first guess cuts the reasonable portion of the array down to size $ n $ , and at most $ m $ guesses finish up , giving us a total of at most $ m+1 $ guesses . let 's look at the general case of an array of length $ n $ . we can express the number of guesses , in the worst case , as `` the number of times we can repeatedly halve , starting at $ n $ , until we get the value 1 , plus one . '' but that 's inconvenient to write out . fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ . when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search ! compare them below : in the next tutorial , we 'll see how computer scientists characterize the running times of linear search and binary search , using a notation that distills the most important part of the running time and discards the less important parts . this content is a collaboration of dartmouth computer science professors thomas cormen and devin balkcom , plus the khan academy computing curriculum team . the content is licensed cc-by-nc-sa .
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( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ .
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with the given pseudo-code , each `` guess '' is actually two comparisons , `` equal to '' and then `` less than '' , so the maximum comparisons is actually 2* ( math.ceil ( math.log2 ( n ) ) +1 ) right ?
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half . if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 . once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern . every time we double the size of the array , we need at most one more guess . suppose we need at most $ m $ guesses for an array of length $ n $ . then , for an array of length $ 2n $ , the first guess cuts the reasonable portion of the array down to size $ n $ , and at most $ m $ guesses finish up , giving us a total of at most $ m+1 $ guesses . let 's look at the general case of an array of length $ n $ . we can express the number of guesses , in the worst case , as `` the number of times we can repeatedly halve , starting at $ n $ , until we get the value 1 , plus one . '' but that 's inconvenient to write out . fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ . when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search ! compare them below : in the next tutorial , we 'll see how computer scientists characterize the running times of linear search and binary search , using a notation that distills the most important part of the running time and discards the less important parts . this content is a collaboration of dartmouth computer science professors thomas cormen and devin balkcom , plus the khan academy computing curriculum team . the content is licensed cc-by-nc-sa .
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so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses .
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would it not be more efficient to make `` greater than '' the first comparison ?
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half . if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 . once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern . every time we double the size of the array , we need at most one more guess . suppose we need at most $ m $ guesses for an array of length $ n $ . then , for an array of length $ 2n $ , the first guess cuts the reasonable portion of the array down to size $ n $ , and at most $ m $ guesses finish up , giving us a total of at most $ m+1 $ guesses . let 's look at the general case of an array of length $ n $ . we can express the number of guesses , in the worst case , as `` the number of times we can repeatedly halve , starting at $ n $ , until we get the value 1 , plus one . '' but that 's inconvenient to write out . fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ . when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search ! compare them below : in the next tutorial , we 'll see how computer scientists characterize the running times of linear search and binary search , using a notation that distills the most important part of the running time and discards the less important parts . this content is a collaboration of dartmouth computer science professors thomas cormen and devin balkcom , plus the khan academy computing curriculum team . the content is licensed cc-by-nc-sa .
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for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses .
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on the binary search challenge it was a bit confusing that a line : math.floor ( ( min+max ) > > > 1 ) ; produced a message : hm , how are you calculating the new midpoint index ?
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half . if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 . once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern . every time we double the size of the array , we need at most one more guess . suppose we need at most $ m $ guesses for an array of length $ n $ . then , for an array of length $ 2n $ , the first guess cuts the reasonable portion of the array down to size $ n $ , and at most $ m $ guesses finish up , giving us a total of at most $ m+1 $ guesses . let 's look at the general case of an array of length $ n $ . we can express the number of guesses , in the worst case , as `` the number of times we can repeatedly halve , starting at $ n $ , until we get the value 1 , plus one . '' but that 's inconvenient to write out . fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ . when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search ! compare them below : in the next tutorial , we 'll see how computer scientists characterize the running times of linear search and binary search , using a notation that distills the most important part of the running time and discards the less important parts . this content is a collaboration of dartmouth computer science professors thomas cormen and devin balkcom , plus the khan academy computing curriculum team . the content is licensed cc-by-nc-sa .
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( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ .
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why is there a plus 1 ?
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half . if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 . once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern . every time we double the size of the array , we need at most one more guess . suppose we need at most $ m $ guesses for an array of length $ n $ . then , for an array of length $ 2n $ , the first guess cuts the reasonable portion of the array down to size $ n $ , and at most $ m $ guesses finish up , giving us a total of at most $ m+1 $ guesses . let 's look at the general case of an array of length $ n $ . we can express the number of guesses , in the worst case , as `` the number of times we can repeatedly halve , starting at $ n $ , until we get the value 1 , plus one . '' but that 's inconvenient to write out . fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ . when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search ! compare them below : in the next tutorial , we 'll see how computer scientists characterize the running times of linear search and binary search , using a notation that distills the most important part of the running time and discards the less important parts . this content is a collaboration of dartmouth computer science professors thomas cormen and devin balkcom , plus the khan academy computing curriculum team . the content is licensed cc-by-nc-sa .
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if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 .
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the term 'guess ' that we 're using here for binary search , can we call it steps ?
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half . if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 . once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern . every time we double the size of the array , we need at most one more guess . suppose we need at most $ m $ guesses for an array of length $ n $ . then , for an array of length $ 2n $ , the first guess cuts the reasonable portion of the array down to size $ n $ , and at most $ m $ guesses finish up , giving us a total of at most $ m+1 $ guesses . let 's look at the general case of an array of length $ n $ . we can express the number of guesses , in the worst case , as `` the number of times we can repeatedly halve , starting at $ n $ , until we get the value 1 , plus one . '' but that 's inconvenient to write out . fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ . when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search ! compare them below : in the next tutorial , we 'll see how computer scientists characterize the running times of linear search and binary search , using a notation that distills the most important part of the running time and discards the less important parts . this content is a collaboration of dartmouth computer science professors thomas cormen and devin balkcom , plus the khan academy computing curriculum team . the content is licensed cc-by-nc-sa .
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once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ?
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am i just misreading `` running time of binary search '' , which seems to suggest math.ceil ( math.log2 ( a.length ) ) , as i read it ?
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half . if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 . once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern . every time we double the size of the array , we need at most one more guess . suppose we need at most $ m $ guesses for an array of length $ n $ . then , for an array of length $ 2n $ , the first guess cuts the reasonable portion of the array down to size $ n $ , and at most $ m $ guesses finish up , giving us a total of at most $ m+1 $ guesses . let 's look at the general case of an array of length $ n $ . we can express the number of guesses , in the worst case , as `` the number of times we can repeatedly halve , starting at $ n $ , until we get the value 1 , plus one . '' but that 's inconvenient to write out . fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ . when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search ! compare them below : in the next tutorial , we 'll see how computer scientists characterize the running times of linear search and binary search , using a notation that distills the most important part of the running time and discards the less important parts . this content is a collaboration of dartmouth computer science professors thomas cormen and devin balkcom , plus the khan academy computing curriculum team . the content is licensed cc-by-nc-sa .
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so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture .
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for example would n't an array of 16 take at most 4 guesses , not 5 ?
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we know that linear search on an array of $ n $ elements might have to make as many as $ n $ guesses . you probably already have an intuitive idea that binary search makes fewer guesses than linear search . you even might have perceived that the difference between the worst-case number of guesses for linear search and binary search becomes more striking as the array length increases . let 's see how to analyze the maximum number of guesses that binary search makes . the key idea is that when binary search makes an incorrect guess , the portion of the array that contains reasonable guesses is reduced by at least half . if the reasonable portion had 32 elements , then an incorrect guess cuts it down to have at most 16 . binary search halves the size of the reasonable portion upon every incorrect guess . if we start with an array of length 8 , then incorrect guesses reduce the size of the reasonable portion to 4 , then 2 , and then 1 . once the reasonable portion contains just one element , no further guesses occur ; the guess for the 1-element portion is either correct or incorrect , and we 're done . so with an array of length 8 , binary search needs at most four guesses . what do you think would happen with an array of 16 elements ? if you said that the first guess would eliminate at least 8 elements , so that at most 8 remain , you 're getting the picture . so with 16 elements , we need at most five guesses . by now , you 're probably seeing the pattern . every time we double the size of the array , we need at most one more guess . suppose we need at most $ m $ guesses for an array of length $ n $ . then , for an array of length $ 2n $ , the first guess cuts the reasonable portion of the array down to size $ n $ , and at most $ m $ guesses finish up , giving us a total of at most $ m+1 $ guesses . let 's look at the general case of an array of length $ n $ . we can express the number of guesses , in the worst case , as `` the number of times we can repeatedly halve , starting at $ n $ , until we get the value 1 , plus one . '' but that 's inconvenient to write out . fortunately , there 's a mathematical function that means the same thing as the number of times we repeatedly halve , starting at $ n $ , until we get the value 1 : the base-2 logarithm of $ n $ . we write it as $ \lg n $ . ( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ . for example , because $ \lg 128 = 7 $ , we know that $ 2^7 = 128 $ . when $ n $ is not a power of 2 , we can just go up to the next higher power of 2 . for an array whose length is 1000 , the next higher power of 2 is 1024 , which equals $ 2^ { 10 } $ . therefore , for a 1000-element array , binary search would require at most 11 ( 10 + 1 ) guesses . for the tycho-2 star catalog with 2,539,913 stars , the next higher power of 2 is $ 2^ { 22 } $ ( which is 4,194,304 ) , and we would need at most 23 guesses . much better than linear search ! compare them below : in the next tutorial , we 'll see how computer scientists characterize the running times of linear search and binary search , using a notation that distills the most important part of the running time and discards the less important parts . this content is a collaboration of dartmouth computer science professors thomas cormen and devin balkcom , plus the khan academy computing curriculum team . the content is licensed cc-by-nc-sa .
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( you can learn more about logarithms here . ) here 's a table showing the base-2 logarithms of various values of $ n $ : | $ n $ | $ \lg n $ | | -- - | -- - | | 1 | 0 | | 2 | 1 | | 4 | 2 | | 8 | 3 | | 16 | 4 | | 32 | 5 | | 64 | 6 | | 128 | 7 | | 256 | 8 | | 512 | 9 | | 1024 | 10 | | 1,048,576 | 20 | | 2,097,152 | 21 | we can view this same table as a chart : zooming in on smaller values of n : the logarithm function grows very slowly . logarithms are the inverse of exponentials , which grow very rapidly , so that if $ \lg n = x $ , then $ n = 2^x $ .
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m+1 makes sense when you double your size it takes 1 more guess but where does the rule for n+1 come in ?
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what is thermal conduction ? walking on bathroom tile in winter is annoying since it feels so much colder than the carpet . this is interesting , since the carpet and tile are usually both at the same temperature ( i.e . the temperature of the interior of the house ) . the different sensations we feel is explained by the fact that different materials transfer heat at different rates . tile and stone conduct heat more rapidly than carpet and fabrics , so tile and stone feel colder in winter since they transfer heat out of your foot faster than the carpet does . in general , good conductors of electricity ( metals like copper , aluminum , gold , and silver ) are also good heat conductors , whereas insulators of electricity ( wood , plastic , and rubber ) are poor heat conductors . the figure below shows molecules in two bodies at different temperatures . the ( average ) kinetic energy of a molecule in the hot body is higher than in the colder body . if two molecules collide , an energy transfer from the hot to the cold molecule occurs . the cumulative effect from all collisions results in a net flux of heat from the hot body to the colder body . we call this transfer of heat between two objects in contact thermal conduction . image : the molecules in two bodies at different temperatures have different average kinetic energies . collisions occurring at the contact surface tend to transfer energy from high-temperature regions to low-temperature regions . ( image credit : openstax college physics ) what 's the equation for the rate of thermal conduction ? there are four factors ( $ k $ , $ a $ , $ \delta t $ , $ d $ ) that affect the rate at which heat is conducted through a material . these four factors are included in the equation below that was deduced from and is confirmed by experiments . $ \large \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ the letter $ q $ represents the amount of heat transferred in a time $ t $ , $ k $ is the thermal conductivity constant for the material , $ a $ is the cross sectional area of the material transferring heat , $ \delta t $ is the difference in temperature between one side of the material and the other , and $ d $ is the thickness of the material . these factors can be seen visually in the diagram below . image : heat conduction occurs through any material , represented here by a rectangular bar , whether window glass or walrus blubber . ( image credit : openstax college physics ) what does each term represent in the thermal conduction equation ? there 's a lot to digest in the equation for thermal conduction $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ . let 's look at what each factor means individually below . $ \dfrac { q } { t } $ : the factor on the left hand side of the equation $ ( \dfrac { q } { t } ) $ represents the number of $ \text { joules } $ of heat energy transferred through the material per $ \text { second } $ . this means the quantity $ \dfrac { q } { t } $ has units of $ \dfrac { \text { joules } } { \text { second } } =\text { watts } $ . $ k $ : the factor $ k $ is called the thermal conductivity constant . the thermal conductivity constant $ k $ is larger for materials that transfer heat well ( like metal and stone ) , and $ k $ is small for materials that transfer heat poorly ( like air and wood ) . $ \delta t $ : the heat flow is proportional to the temperature difference $ \delta t=t_ { hot } -t_ { cold } $ between one end of the conducting material and the other end . therefore , you will get a more severe burn from boiling water than from hot tap water . conversely , if the temperatures are the same , the net heat transfer rate falls to zero , and equilibrium is achieved . $ a $ : owing to the fact that the number of collisions increases with increasing area , heat conduction depends on the cross-sectional area $ a $ . if you touch a cold wall with your palm , your hand cools faster than if you just touch it with your fingertip . $ d $ : a third factor in the mechanism of conduction is the thickness $ d $ of the material through which heat transfers . the figure above shows a slab of material with different temperatures on either side . suppose that $ t_2 $ is greater than $ t_1 $ , so that heat is transferred from left to right . heat transfer from the left side to the right side is accomplished by a series of molecular collisions . the thicker the material , the more time it takes to transfer the same amount of heat . this model explains why thick clothing is warmer than thin clothing in winters , and why arctic mammals protect themselves with thick blubber . why do metals feel both colder in the winter , and hotter in the summer ? materials with a high thermal conductivity constant $ k $ ( like metals and stones ) will conduct heat well both ways ; into or out of the material . so if your skin comes into contact with metal that is colder than your skin temperature , the metal can rapidly transfer heat energy out of your hand , making the metal feel particularly cold . similarly , if the metal is hotter than your skin temperature , the metal can rapidly transfer heat energy into your hand , making the metal feel particularly hot . this is why concrete will feel especially cold to our bare feet in winter ( the concrete transfers heat out of our feet rapidly ) , and especially hot to our bare feet in summer ( the concrete transfers heat into our feet rapidly ) . what do solved examples involving thermal conduction look like ? example 1 : window makeover a person wants to replace the window on their house , but they do n't want their heating and cooling bills to change . the original window on the wall of the house has area $ a $ , thickness $ d $ , and is made out of glass that has a thermal conduction constant $ k $ . which one of the following changes could be made to the window that would leave the rate of thermal conduction the same as the original window ? ( select one ) example 2 : window heat loss a single-paned window in your house is $ 0.65\text { m } $ wide , $ 1.25\text { m } $ tall , and has a thickness of $ 2\text { cm } $ . the glass has a thermal conduction constant of $ 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } $ . assume the outside temperature of the glass is a constant $ 5^o\text { c } $ and the inside temperature of the glass is a constant $ 20^o\text { c } $ . how many $ \text { joules } $ of heat are transferred out of the window in one hour ? solution : $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } \quad { \text { ( start with the formula for the rate of thermal conduction ) } } $ $ q=\dfrac { tka\delta t } { d } \quad { \text { ( multiply both sides by $ t $ to isolate $ q $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ka\delta t } { d } \quad { \text { ( the time interval is $ 1 \text { hour } $ , which is $ 3600 \text { seconds } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) a\delta t } { d } \quad { \text { ( plug in the $ k $ value for the glass ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) \delta t } { d } \quad { \text { ( the area is $ \text { height } \times \text { width } =0.65\text { m } \times1.25\text { m } =0.8125\text { m } ^2 $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { d } \quad { \text { ( $ \delta t=t_ { hot } -t_ { cold } =20^o\text { c } -5^o\text { c } =15^o\text { c } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { 0.02\text { m } } \quad { \text { ( the thickness $ d $ must be in meters , $ 2\text { cm } =0.02\text { m } $ ) } } $ $ q= 1.84 \times 10^6 \text { j } \quad { \text { ( calculate and celebrate ) } } \quad $
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image : the molecules in two bodies at different temperatures have different average kinetic energies . collisions occurring at the contact surface tend to transfer energy from high-temperature regions to low-temperature regions . ( image credit : openstax college physics ) what 's the equation for the rate of thermal conduction ?
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but i 'm still curious about what determine the temperature of atmosphere ?
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what is thermal conduction ? walking on bathroom tile in winter is annoying since it feels so much colder than the carpet . this is interesting , since the carpet and tile are usually both at the same temperature ( i.e . the temperature of the interior of the house ) . the different sensations we feel is explained by the fact that different materials transfer heat at different rates . tile and stone conduct heat more rapidly than carpet and fabrics , so tile and stone feel colder in winter since they transfer heat out of your foot faster than the carpet does . in general , good conductors of electricity ( metals like copper , aluminum , gold , and silver ) are also good heat conductors , whereas insulators of electricity ( wood , plastic , and rubber ) are poor heat conductors . the figure below shows molecules in two bodies at different temperatures . the ( average ) kinetic energy of a molecule in the hot body is higher than in the colder body . if two molecules collide , an energy transfer from the hot to the cold molecule occurs . the cumulative effect from all collisions results in a net flux of heat from the hot body to the colder body . we call this transfer of heat between two objects in contact thermal conduction . image : the molecules in two bodies at different temperatures have different average kinetic energies . collisions occurring at the contact surface tend to transfer energy from high-temperature regions to low-temperature regions . ( image credit : openstax college physics ) what 's the equation for the rate of thermal conduction ? there are four factors ( $ k $ , $ a $ , $ \delta t $ , $ d $ ) that affect the rate at which heat is conducted through a material . these four factors are included in the equation below that was deduced from and is confirmed by experiments . $ \large \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ the letter $ q $ represents the amount of heat transferred in a time $ t $ , $ k $ is the thermal conductivity constant for the material , $ a $ is the cross sectional area of the material transferring heat , $ \delta t $ is the difference in temperature between one side of the material and the other , and $ d $ is the thickness of the material . these factors can be seen visually in the diagram below . image : heat conduction occurs through any material , represented here by a rectangular bar , whether window glass or walrus blubber . ( image credit : openstax college physics ) what does each term represent in the thermal conduction equation ? there 's a lot to digest in the equation for thermal conduction $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ . let 's look at what each factor means individually below . $ \dfrac { q } { t } $ : the factor on the left hand side of the equation $ ( \dfrac { q } { t } ) $ represents the number of $ \text { joules } $ of heat energy transferred through the material per $ \text { second } $ . this means the quantity $ \dfrac { q } { t } $ has units of $ \dfrac { \text { joules } } { \text { second } } =\text { watts } $ . $ k $ : the factor $ k $ is called the thermal conductivity constant . the thermal conductivity constant $ k $ is larger for materials that transfer heat well ( like metal and stone ) , and $ k $ is small for materials that transfer heat poorly ( like air and wood ) . $ \delta t $ : the heat flow is proportional to the temperature difference $ \delta t=t_ { hot } -t_ { cold } $ between one end of the conducting material and the other end . therefore , you will get a more severe burn from boiling water than from hot tap water . conversely , if the temperatures are the same , the net heat transfer rate falls to zero , and equilibrium is achieved . $ a $ : owing to the fact that the number of collisions increases with increasing area , heat conduction depends on the cross-sectional area $ a $ . if you touch a cold wall with your palm , your hand cools faster than if you just touch it with your fingertip . $ d $ : a third factor in the mechanism of conduction is the thickness $ d $ of the material through which heat transfers . the figure above shows a slab of material with different temperatures on either side . suppose that $ t_2 $ is greater than $ t_1 $ , so that heat is transferred from left to right . heat transfer from the left side to the right side is accomplished by a series of molecular collisions . the thicker the material , the more time it takes to transfer the same amount of heat . this model explains why thick clothing is warmer than thin clothing in winters , and why arctic mammals protect themselves with thick blubber . why do metals feel both colder in the winter , and hotter in the summer ? materials with a high thermal conductivity constant $ k $ ( like metals and stones ) will conduct heat well both ways ; into or out of the material . so if your skin comes into contact with metal that is colder than your skin temperature , the metal can rapidly transfer heat energy out of your hand , making the metal feel particularly cold . similarly , if the metal is hotter than your skin temperature , the metal can rapidly transfer heat energy into your hand , making the metal feel particularly hot . this is why concrete will feel especially cold to our bare feet in winter ( the concrete transfers heat out of our feet rapidly ) , and especially hot to our bare feet in summer ( the concrete transfers heat into our feet rapidly ) . what do solved examples involving thermal conduction look like ? example 1 : window makeover a person wants to replace the window on their house , but they do n't want their heating and cooling bills to change . the original window on the wall of the house has area $ a $ , thickness $ d $ , and is made out of glass that has a thermal conduction constant $ k $ . which one of the following changes could be made to the window that would leave the rate of thermal conduction the same as the original window ? ( select one ) example 2 : window heat loss a single-paned window in your house is $ 0.65\text { m } $ wide , $ 1.25\text { m } $ tall , and has a thickness of $ 2\text { cm } $ . the glass has a thermal conduction constant of $ 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } $ . assume the outside temperature of the glass is a constant $ 5^o\text { c } $ and the inside temperature of the glass is a constant $ 20^o\text { c } $ . how many $ \text { joules } $ of heat are transferred out of the window in one hour ? solution : $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } \quad { \text { ( start with the formula for the rate of thermal conduction ) } } $ $ q=\dfrac { tka\delta t } { d } \quad { \text { ( multiply both sides by $ t $ to isolate $ q $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ka\delta t } { d } \quad { \text { ( the time interval is $ 1 \text { hour } $ , which is $ 3600 \text { seconds } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) a\delta t } { d } \quad { \text { ( plug in the $ k $ value for the glass ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) \delta t } { d } \quad { \text { ( the area is $ \text { height } \times \text { width } =0.65\text { m } \times1.25\text { m } =0.8125\text { m } ^2 $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { d } \quad { \text { ( $ \delta t=t_ { hot } -t_ { cold } =20^o\text { c } -5^o\text { c } =15^o\text { c } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { 0.02\text { m } } \quad { \text { ( the thickness $ d $ must be in meters , $ 2\text { cm } =0.02\text { m } $ ) } } $ $ q= 1.84 \times 10^6 \text { j } \quad { \text { ( calculate and celebrate ) } } \quad $
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what is thermal conduction ? walking on bathroom tile in winter is annoying since it feels so much colder than the carpet .
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the radiation of sun perhaps ?
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what is thermal conduction ? walking on bathroom tile in winter is annoying since it feels so much colder than the carpet . this is interesting , since the carpet and tile are usually both at the same temperature ( i.e . the temperature of the interior of the house ) . the different sensations we feel is explained by the fact that different materials transfer heat at different rates . tile and stone conduct heat more rapidly than carpet and fabrics , so tile and stone feel colder in winter since they transfer heat out of your foot faster than the carpet does . in general , good conductors of electricity ( metals like copper , aluminum , gold , and silver ) are also good heat conductors , whereas insulators of electricity ( wood , plastic , and rubber ) are poor heat conductors . the figure below shows molecules in two bodies at different temperatures . the ( average ) kinetic energy of a molecule in the hot body is higher than in the colder body . if two molecules collide , an energy transfer from the hot to the cold molecule occurs . the cumulative effect from all collisions results in a net flux of heat from the hot body to the colder body . we call this transfer of heat between two objects in contact thermal conduction . image : the molecules in two bodies at different temperatures have different average kinetic energies . collisions occurring at the contact surface tend to transfer energy from high-temperature regions to low-temperature regions . ( image credit : openstax college physics ) what 's the equation for the rate of thermal conduction ? there are four factors ( $ k $ , $ a $ , $ \delta t $ , $ d $ ) that affect the rate at which heat is conducted through a material . these four factors are included in the equation below that was deduced from and is confirmed by experiments . $ \large \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ the letter $ q $ represents the amount of heat transferred in a time $ t $ , $ k $ is the thermal conductivity constant for the material , $ a $ is the cross sectional area of the material transferring heat , $ \delta t $ is the difference in temperature between one side of the material and the other , and $ d $ is the thickness of the material . these factors can be seen visually in the diagram below . image : heat conduction occurs through any material , represented here by a rectangular bar , whether window glass or walrus blubber . ( image credit : openstax college physics ) what does each term represent in the thermal conduction equation ? there 's a lot to digest in the equation for thermal conduction $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ . let 's look at what each factor means individually below . $ \dfrac { q } { t } $ : the factor on the left hand side of the equation $ ( \dfrac { q } { t } ) $ represents the number of $ \text { joules } $ of heat energy transferred through the material per $ \text { second } $ . this means the quantity $ \dfrac { q } { t } $ has units of $ \dfrac { \text { joules } } { \text { second } } =\text { watts } $ . $ k $ : the factor $ k $ is called the thermal conductivity constant . the thermal conductivity constant $ k $ is larger for materials that transfer heat well ( like metal and stone ) , and $ k $ is small for materials that transfer heat poorly ( like air and wood ) . $ \delta t $ : the heat flow is proportional to the temperature difference $ \delta t=t_ { hot } -t_ { cold } $ between one end of the conducting material and the other end . therefore , you will get a more severe burn from boiling water than from hot tap water . conversely , if the temperatures are the same , the net heat transfer rate falls to zero , and equilibrium is achieved . $ a $ : owing to the fact that the number of collisions increases with increasing area , heat conduction depends on the cross-sectional area $ a $ . if you touch a cold wall with your palm , your hand cools faster than if you just touch it with your fingertip . $ d $ : a third factor in the mechanism of conduction is the thickness $ d $ of the material through which heat transfers . the figure above shows a slab of material with different temperatures on either side . suppose that $ t_2 $ is greater than $ t_1 $ , so that heat is transferred from left to right . heat transfer from the left side to the right side is accomplished by a series of molecular collisions . the thicker the material , the more time it takes to transfer the same amount of heat . this model explains why thick clothing is warmer than thin clothing in winters , and why arctic mammals protect themselves with thick blubber . why do metals feel both colder in the winter , and hotter in the summer ? materials with a high thermal conductivity constant $ k $ ( like metals and stones ) will conduct heat well both ways ; into or out of the material . so if your skin comes into contact with metal that is colder than your skin temperature , the metal can rapidly transfer heat energy out of your hand , making the metal feel particularly cold . similarly , if the metal is hotter than your skin temperature , the metal can rapidly transfer heat energy into your hand , making the metal feel particularly hot . this is why concrete will feel especially cold to our bare feet in winter ( the concrete transfers heat out of our feet rapidly ) , and especially hot to our bare feet in summer ( the concrete transfers heat into our feet rapidly ) . what do solved examples involving thermal conduction look like ? example 1 : window makeover a person wants to replace the window on their house , but they do n't want their heating and cooling bills to change . the original window on the wall of the house has area $ a $ , thickness $ d $ , and is made out of glass that has a thermal conduction constant $ k $ . which one of the following changes could be made to the window that would leave the rate of thermal conduction the same as the original window ? ( select one ) example 2 : window heat loss a single-paned window in your house is $ 0.65\text { m } $ wide , $ 1.25\text { m } $ tall , and has a thickness of $ 2\text { cm } $ . the glass has a thermal conduction constant of $ 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } $ . assume the outside temperature of the glass is a constant $ 5^o\text { c } $ and the inside temperature of the glass is a constant $ 20^o\text { c } $ . how many $ \text { joules } $ of heat are transferred out of the window in one hour ? solution : $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } \quad { \text { ( start with the formula for the rate of thermal conduction ) } } $ $ q=\dfrac { tka\delta t } { d } \quad { \text { ( multiply both sides by $ t $ to isolate $ q $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ka\delta t } { d } \quad { \text { ( the time interval is $ 1 \text { hour } $ , which is $ 3600 \text { seconds } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) a\delta t } { d } \quad { \text { ( plug in the $ k $ value for the glass ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) \delta t } { d } \quad { \text { ( the area is $ \text { height } \times \text { width } =0.65\text { m } \times1.25\text { m } =0.8125\text { m } ^2 $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { d } \quad { \text { ( $ \delta t=t_ { hot } -t_ { cold } =20^o\text { c } -5^o\text { c } =15^o\text { c } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { 0.02\text { m } } \quad { \text { ( the thickness $ d $ must be in meters , $ 2\text { cm } =0.02\text { m } $ ) } } $ $ q= 1.84 \times 10^6 \text { j } \quad { \text { ( calculate and celebrate ) } } \quad $
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what is thermal conduction ? walking on bathroom tile in winter is annoying since it feels so much colder than the carpet .
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can you say that liquid water is a bad thermal conductor ?
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what is thermal conduction ? walking on bathroom tile in winter is annoying since it feels so much colder than the carpet . this is interesting , since the carpet and tile are usually both at the same temperature ( i.e . the temperature of the interior of the house ) . the different sensations we feel is explained by the fact that different materials transfer heat at different rates . tile and stone conduct heat more rapidly than carpet and fabrics , so tile and stone feel colder in winter since they transfer heat out of your foot faster than the carpet does . in general , good conductors of electricity ( metals like copper , aluminum , gold , and silver ) are also good heat conductors , whereas insulators of electricity ( wood , plastic , and rubber ) are poor heat conductors . the figure below shows molecules in two bodies at different temperatures . the ( average ) kinetic energy of a molecule in the hot body is higher than in the colder body . if two molecules collide , an energy transfer from the hot to the cold molecule occurs . the cumulative effect from all collisions results in a net flux of heat from the hot body to the colder body . we call this transfer of heat between two objects in contact thermal conduction . image : the molecules in two bodies at different temperatures have different average kinetic energies . collisions occurring at the contact surface tend to transfer energy from high-temperature regions to low-temperature regions . ( image credit : openstax college physics ) what 's the equation for the rate of thermal conduction ? there are four factors ( $ k $ , $ a $ , $ \delta t $ , $ d $ ) that affect the rate at which heat is conducted through a material . these four factors are included in the equation below that was deduced from and is confirmed by experiments . $ \large \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ the letter $ q $ represents the amount of heat transferred in a time $ t $ , $ k $ is the thermal conductivity constant for the material , $ a $ is the cross sectional area of the material transferring heat , $ \delta t $ is the difference in temperature between one side of the material and the other , and $ d $ is the thickness of the material . these factors can be seen visually in the diagram below . image : heat conduction occurs through any material , represented here by a rectangular bar , whether window glass or walrus blubber . ( image credit : openstax college physics ) what does each term represent in the thermal conduction equation ? there 's a lot to digest in the equation for thermal conduction $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ . let 's look at what each factor means individually below . $ \dfrac { q } { t } $ : the factor on the left hand side of the equation $ ( \dfrac { q } { t } ) $ represents the number of $ \text { joules } $ of heat energy transferred through the material per $ \text { second } $ . this means the quantity $ \dfrac { q } { t } $ has units of $ \dfrac { \text { joules } } { \text { second } } =\text { watts } $ . $ k $ : the factor $ k $ is called the thermal conductivity constant . the thermal conductivity constant $ k $ is larger for materials that transfer heat well ( like metal and stone ) , and $ k $ is small for materials that transfer heat poorly ( like air and wood ) . $ \delta t $ : the heat flow is proportional to the temperature difference $ \delta t=t_ { hot } -t_ { cold } $ between one end of the conducting material and the other end . therefore , you will get a more severe burn from boiling water than from hot tap water . conversely , if the temperatures are the same , the net heat transfer rate falls to zero , and equilibrium is achieved . $ a $ : owing to the fact that the number of collisions increases with increasing area , heat conduction depends on the cross-sectional area $ a $ . if you touch a cold wall with your palm , your hand cools faster than if you just touch it with your fingertip . $ d $ : a third factor in the mechanism of conduction is the thickness $ d $ of the material through which heat transfers . the figure above shows a slab of material with different temperatures on either side . suppose that $ t_2 $ is greater than $ t_1 $ , so that heat is transferred from left to right . heat transfer from the left side to the right side is accomplished by a series of molecular collisions . the thicker the material , the more time it takes to transfer the same amount of heat . this model explains why thick clothing is warmer than thin clothing in winters , and why arctic mammals protect themselves with thick blubber . why do metals feel both colder in the winter , and hotter in the summer ? materials with a high thermal conductivity constant $ k $ ( like metals and stones ) will conduct heat well both ways ; into or out of the material . so if your skin comes into contact with metal that is colder than your skin temperature , the metal can rapidly transfer heat energy out of your hand , making the metal feel particularly cold . similarly , if the metal is hotter than your skin temperature , the metal can rapidly transfer heat energy into your hand , making the metal feel particularly hot . this is why concrete will feel especially cold to our bare feet in winter ( the concrete transfers heat out of our feet rapidly ) , and especially hot to our bare feet in summer ( the concrete transfers heat into our feet rapidly ) . what do solved examples involving thermal conduction look like ? example 1 : window makeover a person wants to replace the window on their house , but they do n't want their heating and cooling bills to change . the original window on the wall of the house has area $ a $ , thickness $ d $ , and is made out of glass that has a thermal conduction constant $ k $ . which one of the following changes could be made to the window that would leave the rate of thermal conduction the same as the original window ? ( select one ) example 2 : window heat loss a single-paned window in your house is $ 0.65\text { m } $ wide , $ 1.25\text { m } $ tall , and has a thickness of $ 2\text { cm } $ . the glass has a thermal conduction constant of $ 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } $ . assume the outside temperature of the glass is a constant $ 5^o\text { c } $ and the inside temperature of the glass is a constant $ 20^o\text { c } $ . how many $ \text { joules } $ of heat are transferred out of the window in one hour ? solution : $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } \quad { \text { ( start with the formula for the rate of thermal conduction ) } } $ $ q=\dfrac { tka\delta t } { d } \quad { \text { ( multiply both sides by $ t $ to isolate $ q $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ka\delta t } { d } \quad { \text { ( the time interval is $ 1 \text { hour } $ , which is $ 3600 \text { seconds } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) a\delta t } { d } \quad { \text { ( plug in the $ k $ value for the glass ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) \delta t } { d } \quad { \text { ( the area is $ \text { height } \times \text { width } =0.65\text { m } \times1.25\text { m } =0.8125\text { m } ^2 $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { d } \quad { \text { ( $ \delta t=t_ { hot } -t_ { cold } =20^o\text { c } -5^o\text { c } =15^o\text { c } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { 0.02\text { m } } \quad { \text { ( the thickness $ d $ must be in meters , $ 2\text { cm } =0.02\text { m } $ ) } } $ $ q= 1.84 \times 10^6 \text { j } \quad { \text { ( calculate and celebrate ) } } \quad $
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collisions occurring at the contact surface tend to transfer energy from high-temperature regions to low-temperature regions . ( image credit : openstax college physics ) what 's the equation for the rate of thermal conduction ? there are four factors ( $ k $ , $ a $ , $ \delta t $ , $ d $ ) that affect the rate at which heat is conducted through a material . these four factors are included in the equation below that was deduced from and is confirmed by experiments .
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to calculate the rate of heat flow , is it still possible to use the formula as stated in the article ?
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what is thermal conduction ? walking on bathroom tile in winter is annoying since it feels so much colder than the carpet . this is interesting , since the carpet and tile are usually both at the same temperature ( i.e . the temperature of the interior of the house ) . the different sensations we feel is explained by the fact that different materials transfer heat at different rates . tile and stone conduct heat more rapidly than carpet and fabrics , so tile and stone feel colder in winter since they transfer heat out of your foot faster than the carpet does . in general , good conductors of electricity ( metals like copper , aluminum , gold , and silver ) are also good heat conductors , whereas insulators of electricity ( wood , plastic , and rubber ) are poor heat conductors . the figure below shows molecules in two bodies at different temperatures . the ( average ) kinetic energy of a molecule in the hot body is higher than in the colder body . if two molecules collide , an energy transfer from the hot to the cold molecule occurs . the cumulative effect from all collisions results in a net flux of heat from the hot body to the colder body . we call this transfer of heat between two objects in contact thermal conduction . image : the molecules in two bodies at different temperatures have different average kinetic energies . collisions occurring at the contact surface tend to transfer energy from high-temperature regions to low-temperature regions . ( image credit : openstax college physics ) what 's the equation for the rate of thermal conduction ? there are four factors ( $ k $ , $ a $ , $ \delta t $ , $ d $ ) that affect the rate at which heat is conducted through a material . these four factors are included in the equation below that was deduced from and is confirmed by experiments . $ \large \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ the letter $ q $ represents the amount of heat transferred in a time $ t $ , $ k $ is the thermal conductivity constant for the material , $ a $ is the cross sectional area of the material transferring heat , $ \delta t $ is the difference in temperature between one side of the material and the other , and $ d $ is the thickness of the material . these factors can be seen visually in the diagram below . image : heat conduction occurs through any material , represented here by a rectangular bar , whether window glass or walrus blubber . ( image credit : openstax college physics ) what does each term represent in the thermal conduction equation ? there 's a lot to digest in the equation for thermal conduction $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ . let 's look at what each factor means individually below . $ \dfrac { q } { t } $ : the factor on the left hand side of the equation $ ( \dfrac { q } { t } ) $ represents the number of $ \text { joules } $ of heat energy transferred through the material per $ \text { second } $ . this means the quantity $ \dfrac { q } { t } $ has units of $ \dfrac { \text { joules } } { \text { second } } =\text { watts } $ . $ k $ : the factor $ k $ is called the thermal conductivity constant . the thermal conductivity constant $ k $ is larger for materials that transfer heat well ( like metal and stone ) , and $ k $ is small for materials that transfer heat poorly ( like air and wood ) . $ \delta t $ : the heat flow is proportional to the temperature difference $ \delta t=t_ { hot } -t_ { cold } $ between one end of the conducting material and the other end . therefore , you will get a more severe burn from boiling water than from hot tap water . conversely , if the temperatures are the same , the net heat transfer rate falls to zero , and equilibrium is achieved . $ a $ : owing to the fact that the number of collisions increases with increasing area , heat conduction depends on the cross-sectional area $ a $ . if you touch a cold wall with your palm , your hand cools faster than if you just touch it with your fingertip . $ d $ : a third factor in the mechanism of conduction is the thickness $ d $ of the material through which heat transfers . the figure above shows a slab of material with different temperatures on either side . suppose that $ t_2 $ is greater than $ t_1 $ , so that heat is transferred from left to right . heat transfer from the left side to the right side is accomplished by a series of molecular collisions . the thicker the material , the more time it takes to transfer the same amount of heat . this model explains why thick clothing is warmer than thin clothing in winters , and why arctic mammals protect themselves with thick blubber . why do metals feel both colder in the winter , and hotter in the summer ? materials with a high thermal conductivity constant $ k $ ( like metals and stones ) will conduct heat well both ways ; into or out of the material . so if your skin comes into contact with metal that is colder than your skin temperature , the metal can rapidly transfer heat energy out of your hand , making the metal feel particularly cold . similarly , if the metal is hotter than your skin temperature , the metal can rapidly transfer heat energy into your hand , making the metal feel particularly hot . this is why concrete will feel especially cold to our bare feet in winter ( the concrete transfers heat out of our feet rapidly ) , and especially hot to our bare feet in summer ( the concrete transfers heat into our feet rapidly ) . what do solved examples involving thermal conduction look like ? example 1 : window makeover a person wants to replace the window on their house , but they do n't want their heating and cooling bills to change . the original window on the wall of the house has area $ a $ , thickness $ d $ , and is made out of glass that has a thermal conduction constant $ k $ . which one of the following changes could be made to the window that would leave the rate of thermal conduction the same as the original window ? ( select one ) example 2 : window heat loss a single-paned window in your house is $ 0.65\text { m } $ wide , $ 1.25\text { m } $ tall , and has a thickness of $ 2\text { cm } $ . the glass has a thermal conduction constant of $ 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } $ . assume the outside temperature of the glass is a constant $ 5^o\text { c } $ and the inside temperature of the glass is a constant $ 20^o\text { c } $ . how many $ \text { joules } $ of heat are transferred out of the window in one hour ? solution : $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } \quad { \text { ( start with the formula for the rate of thermal conduction ) } } $ $ q=\dfrac { tka\delta t } { d } \quad { \text { ( multiply both sides by $ t $ to isolate $ q $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ka\delta t } { d } \quad { \text { ( the time interval is $ 1 \text { hour } $ , which is $ 3600 \text { seconds } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) a\delta t } { d } \quad { \text { ( plug in the $ k $ value for the glass ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) \delta t } { d } \quad { \text { ( the area is $ \text { height } \times \text { width } =0.65\text { m } \times1.25\text { m } =0.8125\text { m } ^2 $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { d } \quad { \text { ( $ \delta t=t_ { hot } -t_ { cold } =20^o\text { c } -5^o\text { c } =15^o\text { c } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { 0.02\text { m } } \quad { \text { ( the thickness $ d $ must be in meters , $ 2\text { cm } =0.02\text { m } $ ) } } $ $ q= 1.84 \times 10^6 \text { j } \quad { \text { ( calculate and celebrate ) } } \quad $
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$ k $ : the factor $ k $ is called the thermal conductivity constant . the thermal conductivity constant $ k $ is larger for materials that transfer heat well ( like metal and stone ) , and $ k $ is small for materials that transfer heat poorly ( like air and wood ) . $ \delta t $ : the heat flow is proportional to the temperature difference $ \delta t=t_ { hot } -t_ { cold } $ between one end of the conducting material and the other end .
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what if the heat transfer is from inside something cylindrical shaped like a pipe ?
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what is thermal conduction ? walking on bathroom tile in winter is annoying since it feels so much colder than the carpet . this is interesting , since the carpet and tile are usually both at the same temperature ( i.e . the temperature of the interior of the house ) . the different sensations we feel is explained by the fact that different materials transfer heat at different rates . tile and stone conduct heat more rapidly than carpet and fabrics , so tile and stone feel colder in winter since they transfer heat out of your foot faster than the carpet does . in general , good conductors of electricity ( metals like copper , aluminum , gold , and silver ) are also good heat conductors , whereas insulators of electricity ( wood , plastic , and rubber ) are poor heat conductors . the figure below shows molecules in two bodies at different temperatures . the ( average ) kinetic energy of a molecule in the hot body is higher than in the colder body . if two molecules collide , an energy transfer from the hot to the cold molecule occurs . the cumulative effect from all collisions results in a net flux of heat from the hot body to the colder body . we call this transfer of heat between two objects in contact thermal conduction . image : the molecules in two bodies at different temperatures have different average kinetic energies . collisions occurring at the contact surface tend to transfer energy from high-temperature regions to low-temperature regions . ( image credit : openstax college physics ) what 's the equation for the rate of thermal conduction ? there are four factors ( $ k $ , $ a $ , $ \delta t $ , $ d $ ) that affect the rate at which heat is conducted through a material . these four factors are included in the equation below that was deduced from and is confirmed by experiments . $ \large \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ the letter $ q $ represents the amount of heat transferred in a time $ t $ , $ k $ is the thermal conductivity constant for the material , $ a $ is the cross sectional area of the material transferring heat , $ \delta t $ is the difference in temperature between one side of the material and the other , and $ d $ is the thickness of the material . these factors can be seen visually in the diagram below . image : heat conduction occurs through any material , represented here by a rectangular bar , whether window glass or walrus blubber . ( image credit : openstax college physics ) what does each term represent in the thermal conduction equation ? there 's a lot to digest in the equation for thermal conduction $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ . let 's look at what each factor means individually below . $ \dfrac { q } { t } $ : the factor on the left hand side of the equation $ ( \dfrac { q } { t } ) $ represents the number of $ \text { joules } $ of heat energy transferred through the material per $ \text { second } $ . this means the quantity $ \dfrac { q } { t } $ has units of $ \dfrac { \text { joules } } { \text { second } } =\text { watts } $ . $ k $ : the factor $ k $ is called the thermal conductivity constant . the thermal conductivity constant $ k $ is larger for materials that transfer heat well ( like metal and stone ) , and $ k $ is small for materials that transfer heat poorly ( like air and wood ) . $ \delta t $ : the heat flow is proportional to the temperature difference $ \delta t=t_ { hot } -t_ { cold } $ between one end of the conducting material and the other end . therefore , you will get a more severe burn from boiling water than from hot tap water . conversely , if the temperatures are the same , the net heat transfer rate falls to zero , and equilibrium is achieved . $ a $ : owing to the fact that the number of collisions increases with increasing area , heat conduction depends on the cross-sectional area $ a $ . if you touch a cold wall with your palm , your hand cools faster than if you just touch it with your fingertip . $ d $ : a third factor in the mechanism of conduction is the thickness $ d $ of the material through which heat transfers . the figure above shows a slab of material with different temperatures on either side . suppose that $ t_2 $ is greater than $ t_1 $ , so that heat is transferred from left to right . heat transfer from the left side to the right side is accomplished by a series of molecular collisions . the thicker the material , the more time it takes to transfer the same amount of heat . this model explains why thick clothing is warmer than thin clothing in winters , and why arctic mammals protect themselves with thick blubber . why do metals feel both colder in the winter , and hotter in the summer ? materials with a high thermal conductivity constant $ k $ ( like metals and stones ) will conduct heat well both ways ; into or out of the material . so if your skin comes into contact with metal that is colder than your skin temperature , the metal can rapidly transfer heat energy out of your hand , making the metal feel particularly cold . similarly , if the metal is hotter than your skin temperature , the metal can rapidly transfer heat energy into your hand , making the metal feel particularly hot . this is why concrete will feel especially cold to our bare feet in winter ( the concrete transfers heat out of our feet rapidly ) , and especially hot to our bare feet in summer ( the concrete transfers heat into our feet rapidly ) . what do solved examples involving thermal conduction look like ? example 1 : window makeover a person wants to replace the window on their house , but they do n't want their heating and cooling bills to change . the original window on the wall of the house has area $ a $ , thickness $ d $ , and is made out of glass that has a thermal conduction constant $ k $ . which one of the following changes could be made to the window that would leave the rate of thermal conduction the same as the original window ? ( select one ) example 2 : window heat loss a single-paned window in your house is $ 0.65\text { m } $ wide , $ 1.25\text { m } $ tall , and has a thickness of $ 2\text { cm } $ . the glass has a thermal conduction constant of $ 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } $ . assume the outside temperature of the glass is a constant $ 5^o\text { c } $ and the inside temperature of the glass is a constant $ 20^o\text { c } $ . how many $ \text { joules } $ of heat are transferred out of the window in one hour ? solution : $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } \quad { \text { ( start with the formula for the rate of thermal conduction ) } } $ $ q=\dfrac { tka\delta t } { d } \quad { \text { ( multiply both sides by $ t $ to isolate $ q $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ka\delta t } { d } \quad { \text { ( the time interval is $ 1 \text { hour } $ , which is $ 3600 \text { seconds } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) a\delta t } { d } \quad { \text { ( plug in the $ k $ value for the glass ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) \delta t } { d } \quad { \text { ( the area is $ \text { height } \times \text { width } =0.65\text { m } \times1.25\text { m } =0.8125\text { m } ^2 $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { d } \quad { \text { ( $ \delta t=t_ { hot } -t_ { cold } =20^o\text { c } -5^o\text { c } =15^o\text { c } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { 0.02\text { m } } \quad { \text { ( the thickness $ d $ must be in meters , $ 2\text { cm } =0.02\text { m } $ ) } } $ $ q= 1.84 \times 10^6 \text { j } \quad { \text { ( calculate and celebrate ) } } \quad $
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conversely , if the temperatures are the same , the net heat transfer rate falls to zero , and equilibrium is achieved . $ a $ : owing to the fact that the number of collisions increases with increasing area , heat conduction depends on the cross-sectional area $ a $ . if you touch a cold wall with your palm , your hand cools faster than if you just touch it with your fingertip .
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what would area a be ?
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what is thermal conduction ? walking on bathroom tile in winter is annoying since it feels so much colder than the carpet . this is interesting , since the carpet and tile are usually both at the same temperature ( i.e . the temperature of the interior of the house ) . the different sensations we feel is explained by the fact that different materials transfer heat at different rates . tile and stone conduct heat more rapidly than carpet and fabrics , so tile and stone feel colder in winter since they transfer heat out of your foot faster than the carpet does . in general , good conductors of electricity ( metals like copper , aluminum , gold , and silver ) are also good heat conductors , whereas insulators of electricity ( wood , plastic , and rubber ) are poor heat conductors . the figure below shows molecules in two bodies at different temperatures . the ( average ) kinetic energy of a molecule in the hot body is higher than in the colder body . if two molecules collide , an energy transfer from the hot to the cold molecule occurs . the cumulative effect from all collisions results in a net flux of heat from the hot body to the colder body . we call this transfer of heat between two objects in contact thermal conduction . image : the molecules in two bodies at different temperatures have different average kinetic energies . collisions occurring at the contact surface tend to transfer energy from high-temperature regions to low-temperature regions . ( image credit : openstax college physics ) what 's the equation for the rate of thermal conduction ? there are four factors ( $ k $ , $ a $ , $ \delta t $ , $ d $ ) that affect the rate at which heat is conducted through a material . these four factors are included in the equation below that was deduced from and is confirmed by experiments . $ \large \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ the letter $ q $ represents the amount of heat transferred in a time $ t $ , $ k $ is the thermal conductivity constant for the material , $ a $ is the cross sectional area of the material transferring heat , $ \delta t $ is the difference in temperature between one side of the material and the other , and $ d $ is the thickness of the material . these factors can be seen visually in the diagram below . image : heat conduction occurs through any material , represented here by a rectangular bar , whether window glass or walrus blubber . ( image credit : openstax college physics ) what does each term represent in the thermal conduction equation ? there 's a lot to digest in the equation for thermal conduction $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ . let 's look at what each factor means individually below . $ \dfrac { q } { t } $ : the factor on the left hand side of the equation $ ( \dfrac { q } { t } ) $ represents the number of $ \text { joules } $ of heat energy transferred through the material per $ \text { second } $ . this means the quantity $ \dfrac { q } { t } $ has units of $ \dfrac { \text { joules } } { \text { second } } =\text { watts } $ . $ k $ : the factor $ k $ is called the thermal conductivity constant . the thermal conductivity constant $ k $ is larger for materials that transfer heat well ( like metal and stone ) , and $ k $ is small for materials that transfer heat poorly ( like air and wood ) . $ \delta t $ : the heat flow is proportional to the temperature difference $ \delta t=t_ { hot } -t_ { cold } $ between one end of the conducting material and the other end . therefore , you will get a more severe burn from boiling water than from hot tap water . conversely , if the temperatures are the same , the net heat transfer rate falls to zero , and equilibrium is achieved . $ a $ : owing to the fact that the number of collisions increases with increasing area , heat conduction depends on the cross-sectional area $ a $ . if you touch a cold wall with your palm , your hand cools faster than if you just touch it with your fingertip . $ d $ : a third factor in the mechanism of conduction is the thickness $ d $ of the material through which heat transfers . the figure above shows a slab of material with different temperatures on either side . suppose that $ t_2 $ is greater than $ t_1 $ , so that heat is transferred from left to right . heat transfer from the left side to the right side is accomplished by a series of molecular collisions . the thicker the material , the more time it takes to transfer the same amount of heat . this model explains why thick clothing is warmer than thin clothing in winters , and why arctic mammals protect themselves with thick blubber . why do metals feel both colder in the winter , and hotter in the summer ? materials with a high thermal conductivity constant $ k $ ( like metals and stones ) will conduct heat well both ways ; into or out of the material . so if your skin comes into contact with metal that is colder than your skin temperature , the metal can rapidly transfer heat energy out of your hand , making the metal feel particularly cold . similarly , if the metal is hotter than your skin temperature , the metal can rapidly transfer heat energy into your hand , making the metal feel particularly hot . this is why concrete will feel especially cold to our bare feet in winter ( the concrete transfers heat out of our feet rapidly ) , and especially hot to our bare feet in summer ( the concrete transfers heat into our feet rapidly ) . what do solved examples involving thermal conduction look like ? example 1 : window makeover a person wants to replace the window on their house , but they do n't want their heating and cooling bills to change . the original window on the wall of the house has area $ a $ , thickness $ d $ , and is made out of glass that has a thermal conduction constant $ k $ . which one of the following changes could be made to the window that would leave the rate of thermal conduction the same as the original window ? ( select one ) example 2 : window heat loss a single-paned window in your house is $ 0.65\text { m } $ wide , $ 1.25\text { m } $ tall , and has a thickness of $ 2\text { cm } $ . the glass has a thermal conduction constant of $ 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } $ . assume the outside temperature of the glass is a constant $ 5^o\text { c } $ and the inside temperature of the glass is a constant $ 20^o\text { c } $ . how many $ \text { joules } $ of heat are transferred out of the window in one hour ? solution : $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } \quad { \text { ( start with the formula for the rate of thermal conduction ) } } $ $ q=\dfrac { tka\delta t } { d } \quad { \text { ( multiply both sides by $ t $ to isolate $ q $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ka\delta t } { d } \quad { \text { ( the time interval is $ 1 \text { hour } $ , which is $ 3600 \text { seconds } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) a\delta t } { d } \quad { \text { ( plug in the $ k $ value for the glass ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) \delta t } { d } \quad { \text { ( the area is $ \text { height } \times \text { width } =0.65\text { m } \times1.25\text { m } =0.8125\text { m } ^2 $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { d } \quad { \text { ( $ \delta t=t_ { hot } -t_ { cold } =20^o\text { c } -5^o\text { c } =15^o\text { c } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { 0.02\text { m } } \quad { \text { ( the thickness $ d $ must be in meters , $ 2\text { cm } =0.02\text { m } $ ) } } $ $ q= 1.84 \times 10^6 \text { j } \quad { \text { ( calculate and celebrate ) } } \quad $
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the cumulative effect from all collisions results in a net flux of heat from the hot body to the colder body . we call this transfer of heat between two objects in contact thermal conduction . image : the molecules in two bodies at different temperatures have different average kinetic energies .
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how do dynamic and steady state of heat conduction differ from each other ?
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what is thermal conduction ? walking on bathroom tile in winter is annoying since it feels so much colder than the carpet . this is interesting , since the carpet and tile are usually both at the same temperature ( i.e . the temperature of the interior of the house ) . the different sensations we feel is explained by the fact that different materials transfer heat at different rates . tile and stone conduct heat more rapidly than carpet and fabrics , so tile and stone feel colder in winter since they transfer heat out of your foot faster than the carpet does . in general , good conductors of electricity ( metals like copper , aluminum , gold , and silver ) are also good heat conductors , whereas insulators of electricity ( wood , plastic , and rubber ) are poor heat conductors . the figure below shows molecules in two bodies at different temperatures . the ( average ) kinetic energy of a molecule in the hot body is higher than in the colder body . if two molecules collide , an energy transfer from the hot to the cold molecule occurs . the cumulative effect from all collisions results in a net flux of heat from the hot body to the colder body . we call this transfer of heat between two objects in contact thermal conduction . image : the molecules in two bodies at different temperatures have different average kinetic energies . collisions occurring at the contact surface tend to transfer energy from high-temperature regions to low-temperature regions . ( image credit : openstax college physics ) what 's the equation for the rate of thermal conduction ? there are four factors ( $ k $ , $ a $ , $ \delta t $ , $ d $ ) that affect the rate at which heat is conducted through a material . these four factors are included in the equation below that was deduced from and is confirmed by experiments . $ \large \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ the letter $ q $ represents the amount of heat transferred in a time $ t $ , $ k $ is the thermal conductivity constant for the material , $ a $ is the cross sectional area of the material transferring heat , $ \delta t $ is the difference in temperature between one side of the material and the other , and $ d $ is the thickness of the material . these factors can be seen visually in the diagram below . image : heat conduction occurs through any material , represented here by a rectangular bar , whether window glass or walrus blubber . ( image credit : openstax college physics ) what does each term represent in the thermal conduction equation ? there 's a lot to digest in the equation for thermal conduction $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ . let 's look at what each factor means individually below . $ \dfrac { q } { t } $ : the factor on the left hand side of the equation $ ( \dfrac { q } { t } ) $ represents the number of $ \text { joules } $ of heat energy transferred through the material per $ \text { second } $ . this means the quantity $ \dfrac { q } { t } $ has units of $ \dfrac { \text { joules } } { \text { second } } =\text { watts } $ . $ k $ : the factor $ k $ is called the thermal conductivity constant . the thermal conductivity constant $ k $ is larger for materials that transfer heat well ( like metal and stone ) , and $ k $ is small for materials that transfer heat poorly ( like air and wood ) . $ \delta t $ : the heat flow is proportional to the temperature difference $ \delta t=t_ { hot } -t_ { cold } $ between one end of the conducting material and the other end . therefore , you will get a more severe burn from boiling water than from hot tap water . conversely , if the temperatures are the same , the net heat transfer rate falls to zero , and equilibrium is achieved . $ a $ : owing to the fact that the number of collisions increases with increasing area , heat conduction depends on the cross-sectional area $ a $ . if you touch a cold wall with your palm , your hand cools faster than if you just touch it with your fingertip . $ d $ : a third factor in the mechanism of conduction is the thickness $ d $ of the material through which heat transfers . the figure above shows a slab of material with different temperatures on either side . suppose that $ t_2 $ is greater than $ t_1 $ , so that heat is transferred from left to right . heat transfer from the left side to the right side is accomplished by a series of molecular collisions . the thicker the material , the more time it takes to transfer the same amount of heat . this model explains why thick clothing is warmer than thin clothing in winters , and why arctic mammals protect themselves with thick blubber . why do metals feel both colder in the winter , and hotter in the summer ? materials with a high thermal conductivity constant $ k $ ( like metals and stones ) will conduct heat well both ways ; into or out of the material . so if your skin comes into contact with metal that is colder than your skin temperature , the metal can rapidly transfer heat energy out of your hand , making the metal feel particularly cold . similarly , if the metal is hotter than your skin temperature , the metal can rapidly transfer heat energy into your hand , making the metal feel particularly hot . this is why concrete will feel especially cold to our bare feet in winter ( the concrete transfers heat out of our feet rapidly ) , and especially hot to our bare feet in summer ( the concrete transfers heat into our feet rapidly ) . what do solved examples involving thermal conduction look like ? example 1 : window makeover a person wants to replace the window on their house , but they do n't want their heating and cooling bills to change . the original window on the wall of the house has area $ a $ , thickness $ d $ , and is made out of glass that has a thermal conduction constant $ k $ . which one of the following changes could be made to the window that would leave the rate of thermal conduction the same as the original window ? ( select one ) example 2 : window heat loss a single-paned window in your house is $ 0.65\text { m } $ wide , $ 1.25\text { m } $ tall , and has a thickness of $ 2\text { cm } $ . the glass has a thermal conduction constant of $ 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } $ . assume the outside temperature of the glass is a constant $ 5^o\text { c } $ and the inside temperature of the glass is a constant $ 20^o\text { c } $ . how many $ \text { joules } $ of heat are transferred out of the window in one hour ? solution : $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } \quad { \text { ( start with the formula for the rate of thermal conduction ) } } $ $ q=\dfrac { tka\delta t } { d } \quad { \text { ( multiply both sides by $ t $ to isolate $ q $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ka\delta t } { d } \quad { \text { ( the time interval is $ 1 \text { hour } $ , which is $ 3600 \text { seconds } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) a\delta t } { d } \quad { \text { ( plug in the $ k $ value for the glass ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) \delta t } { d } \quad { \text { ( the area is $ \text { height } \times \text { width } =0.65\text { m } \times1.25\text { m } =0.8125\text { m } ^2 $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { d } \quad { \text { ( $ \delta t=t_ { hot } -t_ { cold } =20^o\text { c } -5^o\text { c } =15^o\text { c } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { 0.02\text { m } } \quad { \text { ( the thickness $ d $ must be in meters , $ 2\text { cm } =0.02\text { m } $ ) } } $ $ q= 1.84 \times 10^6 \text { j } \quad { \text { ( calculate and celebrate ) } } \quad $
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the ( average ) kinetic energy of a molecule in the hot body is higher than in the colder body . if two molecules collide , an energy transfer from the hot to the cold molecule occurs . the cumulative effect from all collisions results in a net flux of heat from the hot body to the colder body .
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so the sensation of something being hot or cold is simply the transfer of heat energy into or out of a system ?
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what is thermal conduction ? walking on bathroom tile in winter is annoying since it feels so much colder than the carpet . this is interesting , since the carpet and tile are usually both at the same temperature ( i.e . the temperature of the interior of the house ) . the different sensations we feel is explained by the fact that different materials transfer heat at different rates . tile and stone conduct heat more rapidly than carpet and fabrics , so tile and stone feel colder in winter since they transfer heat out of your foot faster than the carpet does . in general , good conductors of electricity ( metals like copper , aluminum , gold , and silver ) are also good heat conductors , whereas insulators of electricity ( wood , plastic , and rubber ) are poor heat conductors . the figure below shows molecules in two bodies at different temperatures . the ( average ) kinetic energy of a molecule in the hot body is higher than in the colder body . if two molecules collide , an energy transfer from the hot to the cold molecule occurs . the cumulative effect from all collisions results in a net flux of heat from the hot body to the colder body . we call this transfer of heat between two objects in contact thermal conduction . image : the molecules in two bodies at different temperatures have different average kinetic energies . collisions occurring at the contact surface tend to transfer energy from high-temperature regions to low-temperature regions . ( image credit : openstax college physics ) what 's the equation for the rate of thermal conduction ? there are four factors ( $ k $ , $ a $ , $ \delta t $ , $ d $ ) that affect the rate at which heat is conducted through a material . these four factors are included in the equation below that was deduced from and is confirmed by experiments . $ \large \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ the letter $ q $ represents the amount of heat transferred in a time $ t $ , $ k $ is the thermal conductivity constant for the material , $ a $ is the cross sectional area of the material transferring heat , $ \delta t $ is the difference in temperature between one side of the material and the other , and $ d $ is the thickness of the material . these factors can be seen visually in the diagram below . image : heat conduction occurs through any material , represented here by a rectangular bar , whether window glass or walrus blubber . ( image credit : openstax college physics ) what does each term represent in the thermal conduction equation ? there 's a lot to digest in the equation for thermal conduction $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ . let 's look at what each factor means individually below . $ \dfrac { q } { t } $ : the factor on the left hand side of the equation $ ( \dfrac { q } { t } ) $ represents the number of $ \text { joules } $ of heat energy transferred through the material per $ \text { second } $ . this means the quantity $ \dfrac { q } { t } $ has units of $ \dfrac { \text { joules } } { \text { second } } =\text { watts } $ . $ k $ : the factor $ k $ is called the thermal conductivity constant . the thermal conductivity constant $ k $ is larger for materials that transfer heat well ( like metal and stone ) , and $ k $ is small for materials that transfer heat poorly ( like air and wood ) . $ \delta t $ : the heat flow is proportional to the temperature difference $ \delta t=t_ { hot } -t_ { cold } $ between one end of the conducting material and the other end . therefore , you will get a more severe burn from boiling water than from hot tap water . conversely , if the temperatures are the same , the net heat transfer rate falls to zero , and equilibrium is achieved . $ a $ : owing to the fact that the number of collisions increases with increasing area , heat conduction depends on the cross-sectional area $ a $ . if you touch a cold wall with your palm , your hand cools faster than if you just touch it with your fingertip . $ d $ : a third factor in the mechanism of conduction is the thickness $ d $ of the material through which heat transfers . the figure above shows a slab of material with different temperatures on either side . suppose that $ t_2 $ is greater than $ t_1 $ , so that heat is transferred from left to right . heat transfer from the left side to the right side is accomplished by a series of molecular collisions . the thicker the material , the more time it takes to transfer the same amount of heat . this model explains why thick clothing is warmer than thin clothing in winters , and why arctic mammals protect themselves with thick blubber . why do metals feel both colder in the winter , and hotter in the summer ? materials with a high thermal conductivity constant $ k $ ( like metals and stones ) will conduct heat well both ways ; into or out of the material . so if your skin comes into contact with metal that is colder than your skin temperature , the metal can rapidly transfer heat energy out of your hand , making the metal feel particularly cold . similarly , if the metal is hotter than your skin temperature , the metal can rapidly transfer heat energy into your hand , making the metal feel particularly hot . this is why concrete will feel especially cold to our bare feet in winter ( the concrete transfers heat out of our feet rapidly ) , and especially hot to our bare feet in summer ( the concrete transfers heat into our feet rapidly ) . what do solved examples involving thermal conduction look like ? example 1 : window makeover a person wants to replace the window on their house , but they do n't want their heating and cooling bills to change . the original window on the wall of the house has area $ a $ , thickness $ d $ , and is made out of glass that has a thermal conduction constant $ k $ . which one of the following changes could be made to the window that would leave the rate of thermal conduction the same as the original window ? ( select one ) example 2 : window heat loss a single-paned window in your house is $ 0.65\text { m } $ wide , $ 1.25\text { m } $ tall , and has a thickness of $ 2\text { cm } $ . the glass has a thermal conduction constant of $ 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } $ . assume the outside temperature of the glass is a constant $ 5^o\text { c } $ and the inside temperature of the glass is a constant $ 20^o\text { c } $ . how many $ \text { joules } $ of heat are transferred out of the window in one hour ? solution : $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } \quad { \text { ( start with the formula for the rate of thermal conduction ) } } $ $ q=\dfrac { tka\delta t } { d } \quad { \text { ( multiply both sides by $ t $ to isolate $ q $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ka\delta t } { d } \quad { \text { ( the time interval is $ 1 \text { hour } $ , which is $ 3600 \text { seconds } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) a\delta t } { d } \quad { \text { ( plug in the $ k $ value for the glass ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) \delta t } { d } \quad { \text { ( the area is $ \text { height } \times \text { width } =0.65\text { m } \times1.25\text { m } =0.8125\text { m } ^2 $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { d } \quad { \text { ( $ \delta t=t_ { hot } -t_ { cold } =20^o\text { c } -5^o\text { c } =15^o\text { c } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { 0.02\text { m } } \quad { \text { ( the thickness $ d $ must be in meters , $ 2\text { cm } =0.02\text { m } $ ) } } $ $ q= 1.84 \times 10^6 \text { j } \quad { \text { ( calculate and celebrate ) } } \quad $
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this means the quantity $ \dfrac { q } { t } $ has units of $ \dfrac { \text { joules } } { \text { second } } =\text { watts } $ . $ k $ : the factor $ k $ is called the thermal conductivity constant . the thermal conductivity constant $ k $ is larger for materials that transfer heat well ( like metal and stone ) , and $ k $ is small for materials that transfer heat poorly ( like air and wood ) .
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what happens to thermal conductivity of a wall if its thickness is doubled ?
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what is thermal conduction ? walking on bathroom tile in winter is annoying since it feels so much colder than the carpet . this is interesting , since the carpet and tile are usually both at the same temperature ( i.e . the temperature of the interior of the house ) . the different sensations we feel is explained by the fact that different materials transfer heat at different rates . tile and stone conduct heat more rapidly than carpet and fabrics , so tile and stone feel colder in winter since they transfer heat out of your foot faster than the carpet does . in general , good conductors of electricity ( metals like copper , aluminum , gold , and silver ) are also good heat conductors , whereas insulators of electricity ( wood , plastic , and rubber ) are poor heat conductors . the figure below shows molecules in two bodies at different temperatures . the ( average ) kinetic energy of a molecule in the hot body is higher than in the colder body . if two molecules collide , an energy transfer from the hot to the cold molecule occurs . the cumulative effect from all collisions results in a net flux of heat from the hot body to the colder body . we call this transfer of heat between two objects in contact thermal conduction . image : the molecules in two bodies at different temperatures have different average kinetic energies . collisions occurring at the contact surface tend to transfer energy from high-temperature regions to low-temperature regions . ( image credit : openstax college physics ) what 's the equation for the rate of thermal conduction ? there are four factors ( $ k $ , $ a $ , $ \delta t $ , $ d $ ) that affect the rate at which heat is conducted through a material . these four factors are included in the equation below that was deduced from and is confirmed by experiments . $ \large \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ the letter $ q $ represents the amount of heat transferred in a time $ t $ , $ k $ is the thermal conductivity constant for the material , $ a $ is the cross sectional area of the material transferring heat , $ \delta t $ is the difference in temperature between one side of the material and the other , and $ d $ is the thickness of the material . these factors can be seen visually in the diagram below . image : heat conduction occurs through any material , represented here by a rectangular bar , whether window glass or walrus blubber . ( image credit : openstax college physics ) what does each term represent in the thermal conduction equation ? there 's a lot to digest in the equation for thermal conduction $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ . let 's look at what each factor means individually below . $ \dfrac { q } { t } $ : the factor on the left hand side of the equation $ ( \dfrac { q } { t } ) $ represents the number of $ \text { joules } $ of heat energy transferred through the material per $ \text { second } $ . this means the quantity $ \dfrac { q } { t } $ has units of $ \dfrac { \text { joules } } { \text { second } } =\text { watts } $ . $ k $ : the factor $ k $ is called the thermal conductivity constant . the thermal conductivity constant $ k $ is larger for materials that transfer heat well ( like metal and stone ) , and $ k $ is small for materials that transfer heat poorly ( like air and wood ) . $ \delta t $ : the heat flow is proportional to the temperature difference $ \delta t=t_ { hot } -t_ { cold } $ between one end of the conducting material and the other end . therefore , you will get a more severe burn from boiling water than from hot tap water . conversely , if the temperatures are the same , the net heat transfer rate falls to zero , and equilibrium is achieved . $ a $ : owing to the fact that the number of collisions increases with increasing area , heat conduction depends on the cross-sectional area $ a $ . if you touch a cold wall with your palm , your hand cools faster than if you just touch it with your fingertip . $ d $ : a third factor in the mechanism of conduction is the thickness $ d $ of the material through which heat transfers . the figure above shows a slab of material with different temperatures on either side . suppose that $ t_2 $ is greater than $ t_1 $ , so that heat is transferred from left to right . heat transfer from the left side to the right side is accomplished by a series of molecular collisions . the thicker the material , the more time it takes to transfer the same amount of heat . this model explains why thick clothing is warmer than thin clothing in winters , and why arctic mammals protect themselves with thick blubber . why do metals feel both colder in the winter , and hotter in the summer ? materials with a high thermal conductivity constant $ k $ ( like metals and stones ) will conduct heat well both ways ; into or out of the material . so if your skin comes into contact with metal that is colder than your skin temperature , the metal can rapidly transfer heat energy out of your hand , making the metal feel particularly cold . similarly , if the metal is hotter than your skin temperature , the metal can rapidly transfer heat energy into your hand , making the metal feel particularly hot . this is why concrete will feel especially cold to our bare feet in winter ( the concrete transfers heat out of our feet rapidly ) , and especially hot to our bare feet in summer ( the concrete transfers heat into our feet rapidly ) . what do solved examples involving thermal conduction look like ? example 1 : window makeover a person wants to replace the window on their house , but they do n't want their heating and cooling bills to change . the original window on the wall of the house has area $ a $ , thickness $ d $ , and is made out of glass that has a thermal conduction constant $ k $ . which one of the following changes could be made to the window that would leave the rate of thermal conduction the same as the original window ? ( select one ) example 2 : window heat loss a single-paned window in your house is $ 0.65\text { m } $ wide , $ 1.25\text { m } $ tall , and has a thickness of $ 2\text { cm } $ . the glass has a thermal conduction constant of $ 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } $ . assume the outside temperature of the glass is a constant $ 5^o\text { c } $ and the inside temperature of the glass is a constant $ 20^o\text { c } $ . how many $ \text { joules } $ of heat are transferred out of the window in one hour ? solution : $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } \quad { \text { ( start with the formula for the rate of thermal conduction ) } } $ $ q=\dfrac { tka\delta t } { d } \quad { \text { ( multiply both sides by $ t $ to isolate $ q $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ka\delta t } { d } \quad { \text { ( the time interval is $ 1 \text { hour } $ , which is $ 3600 \text { seconds } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) a\delta t } { d } \quad { \text { ( plug in the $ k $ value for the glass ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) \delta t } { d } \quad { \text { ( the area is $ \text { height } \times \text { width } =0.65\text { m } \times1.25\text { m } =0.8125\text { m } ^2 $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { d } \quad { \text { ( $ \delta t=t_ { hot } -t_ { cold } =20^o\text { c } -5^o\text { c } =15^o\text { c } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { 0.02\text { m } } \quad { \text { ( the thickness $ d $ must be in meters , $ 2\text { cm } =0.02\text { m } $ ) } } $ $ q= 1.84 \times 10^6 \text { j } \quad { \text { ( calculate and celebrate ) } } \quad $
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this means the quantity $ \dfrac { q } { t } $ has units of $ \dfrac { \text { joules } } { \text { second } } =\text { watts } $ . $ k $ : the factor $ k $ is called the thermal conductivity constant . the thermal conductivity constant $ k $ is larger for materials that transfer heat well ( like metal and stone ) , and $ k $ is small for materials that transfer heat poorly ( like air and wood ) .
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if length is doubled then does thermal conductivity become half ?
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what is thermal conduction ? walking on bathroom tile in winter is annoying since it feels so much colder than the carpet . this is interesting , since the carpet and tile are usually both at the same temperature ( i.e . the temperature of the interior of the house ) . the different sensations we feel is explained by the fact that different materials transfer heat at different rates . tile and stone conduct heat more rapidly than carpet and fabrics , so tile and stone feel colder in winter since they transfer heat out of your foot faster than the carpet does . in general , good conductors of electricity ( metals like copper , aluminum , gold , and silver ) are also good heat conductors , whereas insulators of electricity ( wood , plastic , and rubber ) are poor heat conductors . the figure below shows molecules in two bodies at different temperatures . the ( average ) kinetic energy of a molecule in the hot body is higher than in the colder body . if two molecules collide , an energy transfer from the hot to the cold molecule occurs . the cumulative effect from all collisions results in a net flux of heat from the hot body to the colder body . we call this transfer of heat between two objects in contact thermal conduction . image : the molecules in two bodies at different temperatures have different average kinetic energies . collisions occurring at the contact surface tend to transfer energy from high-temperature regions to low-temperature regions . ( image credit : openstax college physics ) what 's the equation for the rate of thermal conduction ? there are four factors ( $ k $ , $ a $ , $ \delta t $ , $ d $ ) that affect the rate at which heat is conducted through a material . these four factors are included in the equation below that was deduced from and is confirmed by experiments . $ \large \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ the letter $ q $ represents the amount of heat transferred in a time $ t $ , $ k $ is the thermal conductivity constant for the material , $ a $ is the cross sectional area of the material transferring heat , $ \delta t $ is the difference in temperature between one side of the material and the other , and $ d $ is the thickness of the material . these factors can be seen visually in the diagram below . image : heat conduction occurs through any material , represented here by a rectangular bar , whether window glass or walrus blubber . ( image credit : openstax college physics ) what does each term represent in the thermal conduction equation ? there 's a lot to digest in the equation for thermal conduction $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ . let 's look at what each factor means individually below . $ \dfrac { q } { t } $ : the factor on the left hand side of the equation $ ( \dfrac { q } { t } ) $ represents the number of $ \text { joules } $ of heat energy transferred through the material per $ \text { second } $ . this means the quantity $ \dfrac { q } { t } $ has units of $ \dfrac { \text { joules } } { \text { second } } =\text { watts } $ . $ k $ : the factor $ k $ is called the thermal conductivity constant . the thermal conductivity constant $ k $ is larger for materials that transfer heat well ( like metal and stone ) , and $ k $ is small for materials that transfer heat poorly ( like air and wood ) . $ \delta t $ : the heat flow is proportional to the temperature difference $ \delta t=t_ { hot } -t_ { cold } $ between one end of the conducting material and the other end . therefore , you will get a more severe burn from boiling water than from hot tap water . conversely , if the temperatures are the same , the net heat transfer rate falls to zero , and equilibrium is achieved . $ a $ : owing to the fact that the number of collisions increases with increasing area , heat conduction depends on the cross-sectional area $ a $ . if you touch a cold wall with your palm , your hand cools faster than if you just touch it with your fingertip . $ d $ : a third factor in the mechanism of conduction is the thickness $ d $ of the material through which heat transfers . the figure above shows a slab of material with different temperatures on either side . suppose that $ t_2 $ is greater than $ t_1 $ , so that heat is transferred from left to right . heat transfer from the left side to the right side is accomplished by a series of molecular collisions . the thicker the material , the more time it takes to transfer the same amount of heat . this model explains why thick clothing is warmer than thin clothing in winters , and why arctic mammals protect themselves with thick blubber . why do metals feel both colder in the winter , and hotter in the summer ? materials with a high thermal conductivity constant $ k $ ( like metals and stones ) will conduct heat well both ways ; into or out of the material . so if your skin comes into contact with metal that is colder than your skin temperature , the metal can rapidly transfer heat energy out of your hand , making the metal feel particularly cold . similarly , if the metal is hotter than your skin temperature , the metal can rapidly transfer heat energy into your hand , making the metal feel particularly hot . this is why concrete will feel especially cold to our bare feet in winter ( the concrete transfers heat out of our feet rapidly ) , and especially hot to our bare feet in summer ( the concrete transfers heat into our feet rapidly ) . what do solved examples involving thermal conduction look like ? example 1 : window makeover a person wants to replace the window on their house , but they do n't want their heating and cooling bills to change . the original window on the wall of the house has area $ a $ , thickness $ d $ , and is made out of glass that has a thermal conduction constant $ k $ . which one of the following changes could be made to the window that would leave the rate of thermal conduction the same as the original window ? ( select one ) example 2 : window heat loss a single-paned window in your house is $ 0.65\text { m } $ wide , $ 1.25\text { m } $ tall , and has a thickness of $ 2\text { cm } $ . the glass has a thermal conduction constant of $ 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } $ . assume the outside temperature of the glass is a constant $ 5^o\text { c } $ and the inside temperature of the glass is a constant $ 20^o\text { c } $ . how many $ \text { joules } $ of heat are transferred out of the window in one hour ? solution : $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } \quad { \text { ( start with the formula for the rate of thermal conduction ) } } $ $ q=\dfrac { tka\delta t } { d } \quad { \text { ( multiply both sides by $ t $ to isolate $ q $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ka\delta t } { d } \quad { \text { ( the time interval is $ 1 \text { hour } $ , which is $ 3600 \text { seconds } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) a\delta t } { d } \quad { \text { ( plug in the $ k $ value for the glass ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) \delta t } { d } \quad { \text { ( the area is $ \text { height } \times \text { width } =0.65\text { m } \times1.25\text { m } =0.8125\text { m } ^2 $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { d } \quad { \text { ( $ \delta t=t_ { hot } -t_ { cold } =20^o\text { c } -5^o\text { c } =15^o\text { c } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { 0.02\text { m } } \quad { \text { ( the thickness $ d $ must be in meters , $ 2\text { cm } =0.02\text { m } $ ) } } $ $ q= 1.84 \times 10^6 \text { j } \quad { \text { ( calculate and celebrate ) } } \quad $
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the temperature of the interior of the house ) . the different sensations we feel is explained by the fact that different materials transfer heat at different rates . tile and stone conduct heat more rapidly than carpet and fabrics , so tile and stone feel colder in winter since they transfer heat out of your foot faster than the carpet does . in general , good conductors of electricity ( metals like copper , aluminum , gold , and silver ) are also good heat conductors , whereas insulators of electricity ( wood , plastic , and rubber ) are poor heat conductors . the figure below shows molecules in two bodies at different temperatures .
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can we heat a liquid by heating it from above ?
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what is thermal conduction ? walking on bathroom tile in winter is annoying since it feels so much colder than the carpet . this is interesting , since the carpet and tile are usually both at the same temperature ( i.e . the temperature of the interior of the house ) . the different sensations we feel is explained by the fact that different materials transfer heat at different rates . tile and stone conduct heat more rapidly than carpet and fabrics , so tile and stone feel colder in winter since they transfer heat out of your foot faster than the carpet does . in general , good conductors of electricity ( metals like copper , aluminum , gold , and silver ) are also good heat conductors , whereas insulators of electricity ( wood , plastic , and rubber ) are poor heat conductors . the figure below shows molecules in two bodies at different temperatures . the ( average ) kinetic energy of a molecule in the hot body is higher than in the colder body . if two molecules collide , an energy transfer from the hot to the cold molecule occurs . the cumulative effect from all collisions results in a net flux of heat from the hot body to the colder body . we call this transfer of heat between two objects in contact thermal conduction . image : the molecules in two bodies at different temperatures have different average kinetic energies . collisions occurring at the contact surface tend to transfer energy from high-temperature regions to low-temperature regions . ( image credit : openstax college physics ) what 's the equation for the rate of thermal conduction ? there are four factors ( $ k $ , $ a $ , $ \delta t $ , $ d $ ) that affect the rate at which heat is conducted through a material . these four factors are included in the equation below that was deduced from and is confirmed by experiments . $ \large \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ the letter $ q $ represents the amount of heat transferred in a time $ t $ , $ k $ is the thermal conductivity constant for the material , $ a $ is the cross sectional area of the material transferring heat , $ \delta t $ is the difference in temperature between one side of the material and the other , and $ d $ is the thickness of the material . these factors can be seen visually in the diagram below . image : heat conduction occurs through any material , represented here by a rectangular bar , whether window glass or walrus blubber . ( image credit : openstax college physics ) what does each term represent in the thermal conduction equation ? there 's a lot to digest in the equation for thermal conduction $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ . let 's look at what each factor means individually below . $ \dfrac { q } { t } $ : the factor on the left hand side of the equation $ ( \dfrac { q } { t } ) $ represents the number of $ \text { joules } $ of heat energy transferred through the material per $ \text { second } $ . this means the quantity $ \dfrac { q } { t } $ has units of $ \dfrac { \text { joules } } { \text { second } } =\text { watts } $ . $ k $ : the factor $ k $ is called the thermal conductivity constant . the thermal conductivity constant $ k $ is larger for materials that transfer heat well ( like metal and stone ) , and $ k $ is small for materials that transfer heat poorly ( like air and wood ) . $ \delta t $ : the heat flow is proportional to the temperature difference $ \delta t=t_ { hot } -t_ { cold } $ between one end of the conducting material and the other end . therefore , you will get a more severe burn from boiling water than from hot tap water . conversely , if the temperatures are the same , the net heat transfer rate falls to zero , and equilibrium is achieved . $ a $ : owing to the fact that the number of collisions increases with increasing area , heat conduction depends on the cross-sectional area $ a $ . if you touch a cold wall with your palm , your hand cools faster than if you just touch it with your fingertip . $ d $ : a third factor in the mechanism of conduction is the thickness $ d $ of the material through which heat transfers . the figure above shows a slab of material with different temperatures on either side . suppose that $ t_2 $ is greater than $ t_1 $ , so that heat is transferred from left to right . heat transfer from the left side to the right side is accomplished by a series of molecular collisions . the thicker the material , the more time it takes to transfer the same amount of heat . this model explains why thick clothing is warmer than thin clothing in winters , and why arctic mammals protect themselves with thick blubber . why do metals feel both colder in the winter , and hotter in the summer ? materials with a high thermal conductivity constant $ k $ ( like metals and stones ) will conduct heat well both ways ; into or out of the material . so if your skin comes into contact with metal that is colder than your skin temperature , the metal can rapidly transfer heat energy out of your hand , making the metal feel particularly cold . similarly , if the metal is hotter than your skin temperature , the metal can rapidly transfer heat energy into your hand , making the metal feel particularly hot . this is why concrete will feel especially cold to our bare feet in winter ( the concrete transfers heat out of our feet rapidly ) , and especially hot to our bare feet in summer ( the concrete transfers heat into our feet rapidly ) . what do solved examples involving thermal conduction look like ? example 1 : window makeover a person wants to replace the window on their house , but they do n't want their heating and cooling bills to change . the original window on the wall of the house has area $ a $ , thickness $ d $ , and is made out of glass that has a thermal conduction constant $ k $ . which one of the following changes could be made to the window that would leave the rate of thermal conduction the same as the original window ? ( select one ) example 2 : window heat loss a single-paned window in your house is $ 0.65\text { m } $ wide , $ 1.25\text { m } $ tall , and has a thickness of $ 2\text { cm } $ . the glass has a thermal conduction constant of $ 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } $ . assume the outside temperature of the glass is a constant $ 5^o\text { c } $ and the inside temperature of the glass is a constant $ 20^o\text { c } $ . how many $ \text { joules } $ of heat are transferred out of the window in one hour ? solution : $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } \quad { \text { ( start with the formula for the rate of thermal conduction ) } } $ $ q=\dfrac { tka\delta t } { d } \quad { \text { ( multiply both sides by $ t $ to isolate $ q $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ka\delta t } { d } \quad { \text { ( the time interval is $ 1 \text { hour } $ , which is $ 3600 \text { seconds } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) a\delta t } { d } \quad { \text { ( plug in the $ k $ value for the glass ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) \delta t } { d } \quad { \text { ( the area is $ \text { height } \times \text { width } =0.65\text { m } \times1.25\text { m } =0.8125\text { m } ^2 $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { d } \quad { \text { ( $ \delta t=t_ { hot } -t_ { cold } =20^o\text { c } -5^o\text { c } =15^o\text { c } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { 0.02\text { m } } \quad { \text { ( the thickness $ d $ must be in meters , $ 2\text { cm } =0.02\text { m } $ ) } } $ $ q= 1.84 \times 10^6 \text { j } \quad { \text { ( calculate and celebrate ) } } \quad $
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this means the quantity $ \dfrac { q } { t } $ has units of $ \dfrac { \text { joules } } { \text { second } } =\text { watts } $ . $ k $ : the factor $ k $ is called the thermal conductivity constant . the thermal conductivity constant $ k $ is larger for materials that transfer heat well ( like metal and stone ) , and $ k $ is small for materials that transfer heat poorly ( like air and wood ) . $ \delta t $ : the heat flow is proportional to the temperature difference $ \delta t=t_ { hot } -t_ { cold } $ between one end of the conducting material and the other end .
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do the materials that have the temperatures t1 and t2 respectevely have their own k ?
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what is thermal conduction ? walking on bathroom tile in winter is annoying since it feels so much colder than the carpet . this is interesting , since the carpet and tile are usually both at the same temperature ( i.e . the temperature of the interior of the house ) . the different sensations we feel is explained by the fact that different materials transfer heat at different rates . tile and stone conduct heat more rapidly than carpet and fabrics , so tile and stone feel colder in winter since they transfer heat out of your foot faster than the carpet does . in general , good conductors of electricity ( metals like copper , aluminum , gold , and silver ) are also good heat conductors , whereas insulators of electricity ( wood , plastic , and rubber ) are poor heat conductors . the figure below shows molecules in two bodies at different temperatures . the ( average ) kinetic energy of a molecule in the hot body is higher than in the colder body . if two molecules collide , an energy transfer from the hot to the cold molecule occurs . the cumulative effect from all collisions results in a net flux of heat from the hot body to the colder body . we call this transfer of heat between two objects in contact thermal conduction . image : the molecules in two bodies at different temperatures have different average kinetic energies . collisions occurring at the contact surface tend to transfer energy from high-temperature regions to low-temperature regions . ( image credit : openstax college physics ) what 's the equation for the rate of thermal conduction ? there are four factors ( $ k $ , $ a $ , $ \delta t $ , $ d $ ) that affect the rate at which heat is conducted through a material . these four factors are included in the equation below that was deduced from and is confirmed by experiments . $ \large \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ the letter $ q $ represents the amount of heat transferred in a time $ t $ , $ k $ is the thermal conductivity constant for the material , $ a $ is the cross sectional area of the material transferring heat , $ \delta t $ is the difference in temperature between one side of the material and the other , and $ d $ is the thickness of the material . these factors can be seen visually in the diagram below . image : heat conduction occurs through any material , represented here by a rectangular bar , whether window glass or walrus blubber . ( image credit : openstax college physics ) what does each term represent in the thermal conduction equation ? there 's a lot to digest in the equation for thermal conduction $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ . let 's look at what each factor means individually below . $ \dfrac { q } { t } $ : the factor on the left hand side of the equation $ ( \dfrac { q } { t } ) $ represents the number of $ \text { joules } $ of heat energy transferred through the material per $ \text { second } $ . this means the quantity $ \dfrac { q } { t } $ has units of $ \dfrac { \text { joules } } { \text { second } } =\text { watts } $ . $ k $ : the factor $ k $ is called the thermal conductivity constant . the thermal conductivity constant $ k $ is larger for materials that transfer heat well ( like metal and stone ) , and $ k $ is small for materials that transfer heat poorly ( like air and wood ) . $ \delta t $ : the heat flow is proportional to the temperature difference $ \delta t=t_ { hot } -t_ { cold } $ between one end of the conducting material and the other end . therefore , you will get a more severe burn from boiling water than from hot tap water . conversely , if the temperatures are the same , the net heat transfer rate falls to zero , and equilibrium is achieved . $ a $ : owing to the fact that the number of collisions increases with increasing area , heat conduction depends on the cross-sectional area $ a $ . if you touch a cold wall with your palm , your hand cools faster than if you just touch it with your fingertip . $ d $ : a third factor in the mechanism of conduction is the thickness $ d $ of the material through which heat transfers . the figure above shows a slab of material with different temperatures on either side . suppose that $ t_2 $ is greater than $ t_1 $ , so that heat is transferred from left to right . heat transfer from the left side to the right side is accomplished by a series of molecular collisions . the thicker the material , the more time it takes to transfer the same amount of heat . this model explains why thick clothing is warmer than thin clothing in winters , and why arctic mammals protect themselves with thick blubber . why do metals feel both colder in the winter , and hotter in the summer ? materials with a high thermal conductivity constant $ k $ ( like metals and stones ) will conduct heat well both ways ; into or out of the material . so if your skin comes into contact with metal that is colder than your skin temperature , the metal can rapidly transfer heat energy out of your hand , making the metal feel particularly cold . similarly , if the metal is hotter than your skin temperature , the metal can rapidly transfer heat energy into your hand , making the metal feel particularly hot . this is why concrete will feel especially cold to our bare feet in winter ( the concrete transfers heat out of our feet rapidly ) , and especially hot to our bare feet in summer ( the concrete transfers heat into our feet rapidly ) . what do solved examples involving thermal conduction look like ? example 1 : window makeover a person wants to replace the window on their house , but they do n't want their heating and cooling bills to change . the original window on the wall of the house has area $ a $ , thickness $ d $ , and is made out of glass that has a thermal conduction constant $ k $ . which one of the following changes could be made to the window that would leave the rate of thermal conduction the same as the original window ? ( select one ) example 2 : window heat loss a single-paned window in your house is $ 0.65\text { m } $ wide , $ 1.25\text { m } $ tall , and has a thickness of $ 2\text { cm } $ . the glass has a thermal conduction constant of $ 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } $ . assume the outside temperature of the glass is a constant $ 5^o\text { c } $ and the inside temperature of the glass is a constant $ 20^o\text { c } $ . how many $ \text { joules } $ of heat are transferred out of the window in one hour ? solution : $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } \quad { \text { ( start with the formula for the rate of thermal conduction ) } } $ $ q=\dfrac { tka\delta t } { d } \quad { \text { ( multiply both sides by $ t $ to isolate $ q $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ka\delta t } { d } \quad { \text { ( the time interval is $ 1 \text { hour } $ , which is $ 3600 \text { seconds } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) a\delta t } { d } \quad { \text { ( plug in the $ k $ value for the glass ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) \delta t } { d } \quad { \text { ( the area is $ \text { height } \times \text { width } =0.65\text { m } \times1.25\text { m } =0.8125\text { m } ^2 $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { d } \quad { \text { ( $ \delta t=t_ { hot } -t_ { cold } =20^o\text { c } -5^o\text { c } =15^o\text { c } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { 0.02\text { m } } \quad { \text { ( the thickness $ d $ must be in meters , $ 2\text { cm } =0.02\text { m } $ ) } } $ $ q= 1.84 \times 10^6 \text { j } \quad { \text { ( calculate and celebrate ) } } \quad $
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this means the quantity $ \dfrac { q } { t } $ has units of $ \dfrac { \text { joules } } { \text { second } } =\text { watts } $ . $ k $ : the factor $ k $ is called the thermal conductivity constant . the thermal conductivity constant $ k $ is larger for materials that transfer heat well ( like metal and stone ) , and $ k $ is small for materials that transfer heat poorly ( like air and wood ) .
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what happens to the thermal conductivity of a wall if its thickness is doubled ?
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what is thermal conduction ? walking on bathroom tile in winter is annoying since it feels so much colder than the carpet . this is interesting , since the carpet and tile are usually both at the same temperature ( i.e . the temperature of the interior of the house ) . the different sensations we feel is explained by the fact that different materials transfer heat at different rates . tile and stone conduct heat more rapidly than carpet and fabrics , so tile and stone feel colder in winter since they transfer heat out of your foot faster than the carpet does . in general , good conductors of electricity ( metals like copper , aluminum , gold , and silver ) are also good heat conductors , whereas insulators of electricity ( wood , plastic , and rubber ) are poor heat conductors . the figure below shows molecules in two bodies at different temperatures . the ( average ) kinetic energy of a molecule in the hot body is higher than in the colder body . if two molecules collide , an energy transfer from the hot to the cold molecule occurs . the cumulative effect from all collisions results in a net flux of heat from the hot body to the colder body . we call this transfer of heat between two objects in contact thermal conduction . image : the molecules in two bodies at different temperatures have different average kinetic energies . collisions occurring at the contact surface tend to transfer energy from high-temperature regions to low-temperature regions . ( image credit : openstax college physics ) what 's the equation for the rate of thermal conduction ? there are four factors ( $ k $ , $ a $ , $ \delta t $ , $ d $ ) that affect the rate at which heat is conducted through a material . these four factors are included in the equation below that was deduced from and is confirmed by experiments . $ \large \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ the letter $ q $ represents the amount of heat transferred in a time $ t $ , $ k $ is the thermal conductivity constant for the material , $ a $ is the cross sectional area of the material transferring heat , $ \delta t $ is the difference in temperature between one side of the material and the other , and $ d $ is the thickness of the material . these factors can be seen visually in the diagram below . image : heat conduction occurs through any material , represented here by a rectangular bar , whether window glass or walrus blubber . ( image credit : openstax college physics ) what does each term represent in the thermal conduction equation ? there 's a lot to digest in the equation for thermal conduction $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ . let 's look at what each factor means individually below . $ \dfrac { q } { t } $ : the factor on the left hand side of the equation $ ( \dfrac { q } { t } ) $ represents the number of $ \text { joules } $ of heat energy transferred through the material per $ \text { second } $ . this means the quantity $ \dfrac { q } { t } $ has units of $ \dfrac { \text { joules } } { \text { second } } =\text { watts } $ . $ k $ : the factor $ k $ is called the thermal conductivity constant . the thermal conductivity constant $ k $ is larger for materials that transfer heat well ( like metal and stone ) , and $ k $ is small for materials that transfer heat poorly ( like air and wood ) . $ \delta t $ : the heat flow is proportional to the temperature difference $ \delta t=t_ { hot } -t_ { cold } $ between one end of the conducting material and the other end . therefore , you will get a more severe burn from boiling water than from hot tap water . conversely , if the temperatures are the same , the net heat transfer rate falls to zero , and equilibrium is achieved . $ a $ : owing to the fact that the number of collisions increases with increasing area , heat conduction depends on the cross-sectional area $ a $ . if you touch a cold wall with your palm , your hand cools faster than if you just touch it with your fingertip . $ d $ : a third factor in the mechanism of conduction is the thickness $ d $ of the material through which heat transfers . the figure above shows a slab of material with different temperatures on either side . suppose that $ t_2 $ is greater than $ t_1 $ , so that heat is transferred from left to right . heat transfer from the left side to the right side is accomplished by a series of molecular collisions . the thicker the material , the more time it takes to transfer the same amount of heat . this model explains why thick clothing is warmer than thin clothing in winters , and why arctic mammals protect themselves with thick blubber . why do metals feel both colder in the winter , and hotter in the summer ? materials with a high thermal conductivity constant $ k $ ( like metals and stones ) will conduct heat well both ways ; into or out of the material . so if your skin comes into contact with metal that is colder than your skin temperature , the metal can rapidly transfer heat energy out of your hand , making the metal feel particularly cold . similarly , if the metal is hotter than your skin temperature , the metal can rapidly transfer heat energy into your hand , making the metal feel particularly hot . this is why concrete will feel especially cold to our bare feet in winter ( the concrete transfers heat out of our feet rapidly ) , and especially hot to our bare feet in summer ( the concrete transfers heat into our feet rapidly ) . what do solved examples involving thermal conduction look like ? example 1 : window makeover a person wants to replace the window on their house , but they do n't want their heating and cooling bills to change . the original window on the wall of the house has area $ a $ , thickness $ d $ , and is made out of glass that has a thermal conduction constant $ k $ . which one of the following changes could be made to the window that would leave the rate of thermal conduction the same as the original window ? ( select one ) example 2 : window heat loss a single-paned window in your house is $ 0.65\text { m } $ wide , $ 1.25\text { m } $ tall , and has a thickness of $ 2\text { cm } $ . the glass has a thermal conduction constant of $ 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } $ . assume the outside temperature of the glass is a constant $ 5^o\text { c } $ and the inside temperature of the glass is a constant $ 20^o\text { c } $ . how many $ \text { joules } $ of heat are transferred out of the window in one hour ? solution : $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } \quad { \text { ( start with the formula for the rate of thermal conduction ) } } $ $ q=\dfrac { tka\delta t } { d } \quad { \text { ( multiply both sides by $ t $ to isolate $ q $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ka\delta t } { d } \quad { \text { ( the time interval is $ 1 \text { hour } $ , which is $ 3600 \text { seconds } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) a\delta t } { d } \quad { \text { ( plug in the $ k $ value for the glass ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) \delta t } { d } \quad { \text { ( the area is $ \text { height } \times \text { width } =0.65\text { m } \times1.25\text { m } =0.8125\text { m } ^2 $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { d } \quad { \text { ( $ \delta t=t_ { hot } -t_ { cold } =20^o\text { c } -5^o\text { c } =15^o\text { c } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { 0.02\text { m } } \quad { \text { ( the thickness $ d $ must be in meters , $ 2\text { cm } =0.02\text { m } $ ) } } $ $ q= 1.84 \times 10^6 \text { j } \quad { \text { ( calculate and celebrate ) } } \quad $
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walking on bathroom tile in winter is annoying since it feels so much colder than the carpet . this is interesting , since the carpet and tile are usually both at the same temperature ( i.e . the temperature of the interior of the house ) . the different sensations we feel is explained by the fact that different materials transfer heat at different rates .
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is the author really suggesting that , if one were to measure the temperature of the carpet , the tile , and the ambient air temperature in the interior of the house , they would all be exactly the same ?
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what is thermal conduction ? walking on bathroom tile in winter is annoying since it feels so much colder than the carpet . this is interesting , since the carpet and tile are usually both at the same temperature ( i.e . the temperature of the interior of the house ) . the different sensations we feel is explained by the fact that different materials transfer heat at different rates . tile and stone conduct heat more rapidly than carpet and fabrics , so tile and stone feel colder in winter since they transfer heat out of your foot faster than the carpet does . in general , good conductors of electricity ( metals like copper , aluminum , gold , and silver ) are also good heat conductors , whereas insulators of electricity ( wood , plastic , and rubber ) are poor heat conductors . the figure below shows molecules in two bodies at different temperatures . the ( average ) kinetic energy of a molecule in the hot body is higher than in the colder body . if two molecules collide , an energy transfer from the hot to the cold molecule occurs . the cumulative effect from all collisions results in a net flux of heat from the hot body to the colder body . we call this transfer of heat between two objects in contact thermal conduction . image : the molecules in two bodies at different temperatures have different average kinetic energies . collisions occurring at the contact surface tend to transfer energy from high-temperature regions to low-temperature regions . ( image credit : openstax college physics ) what 's the equation for the rate of thermal conduction ? there are four factors ( $ k $ , $ a $ , $ \delta t $ , $ d $ ) that affect the rate at which heat is conducted through a material . these four factors are included in the equation below that was deduced from and is confirmed by experiments . $ \large \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ the letter $ q $ represents the amount of heat transferred in a time $ t $ , $ k $ is the thermal conductivity constant for the material , $ a $ is the cross sectional area of the material transferring heat , $ \delta t $ is the difference in temperature between one side of the material and the other , and $ d $ is the thickness of the material . these factors can be seen visually in the diagram below . image : heat conduction occurs through any material , represented here by a rectangular bar , whether window glass or walrus blubber . ( image credit : openstax college physics ) what does each term represent in the thermal conduction equation ? there 's a lot to digest in the equation for thermal conduction $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ . let 's look at what each factor means individually below . $ \dfrac { q } { t } $ : the factor on the left hand side of the equation $ ( \dfrac { q } { t } ) $ represents the number of $ \text { joules } $ of heat energy transferred through the material per $ \text { second } $ . this means the quantity $ \dfrac { q } { t } $ has units of $ \dfrac { \text { joules } } { \text { second } } =\text { watts } $ . $ k $ : the factor $ k $ is called the thermal conductivity constant . the thermal conductivity constant $ k $ is larger for materials that transfer heat well ( like metal and stone ) , and $ k $ is small for materials that transfer heat poorly ( like air and wood ) . $ \delta t $ : the heat flow is proportional to the temperature difference $ \delta t=t_ { hot } -t_ { cold } $ between one end of the conducting material and the other end . therefore , you will get a more severe burn from boiling water than from hot tap water . conversely , if the temperatures are the same , the net heat transfer rate falls to zero , and equilibrium is achieved . $ a $ : owing to the fact that the number of collisions increases with increasing area , heat conduction depends on the cross-sectional area $ a $ . if you touch a cold wall with your palm , your hand cools faster than if you just touch it with your fingertip . $ d $ : a third factor in the mechanism of conduction is the thickness $ d $ of the material through which heat transfers . the figure above shows a slab of material with different temperatures on either side . suppose that $ t_2 $ is greater than $ t_1 $ , so that heat is transferred from left to right . heat transfer from the left side to the right side is accomplished by a series of molecular collisions . the thicker the material , the more time it takes to transfer the same amount of heat . this model explains why thick clothing is warmer than thin clothing in winters , and why arctic mammals protect themselves with thick blubber . why do metals feel both colder in the winter , and hotter in the summer ? materials with a high thermal conductivity constant $ k $ ( like metals and stones ) will conduct heat well both ways ; into or out of the material . so if your skin comes into contact with metal that is colder than your skin temperature , the metal can rapidly transfer heat energy out of your hand , making the metal feel particularly cold . similarly , if the metal is hotter than your skin temperature , the metal can rapidly transfer heat energy into your hand , making the metal feel particularly hot . this is why concrete will feel especially cold to our bare feet in winter ( the concrete transfers heat out of our feet rapidly ) , and especially hot to our bare feet in summer ( the concrete transfers heat into our feet rapidly ) . what do solved examples involving thermal conduction look like ? example 1 : window makeover a person wants to replace the window on their house , but they do n't want their heating and cooling bills to change . the original window on the wall of the house has area $ a $ , thickness $ d $ , and is made out of glass that has a thermal conduction constant $ k $ . which one of the following changes could be made to the window that would leave the rate of thermal conduction the same as the original window ? ( select one ) example 2 : window heat loss a single-paned window in your house is $ 0.65\text { m } $ wide , $ 1.25\text { m } $ tall , and has a thickness of $ 2\text { cm } $ . the glass has a thermal conduction constant of $ 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } $ . assume the outside temperature of the glass is a constant $ 5^o\text { c } $ and the inside temperature of the glass is a constant $ 20^o\text { c } $ . how many $ \text { joules } $ of heat are transferred out of the window in one hour ? solution : $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } \quad { \text { ( start with the formula for the rate of thermal conduction ) } } $ $ q=\dfrac { tka\delta t } { d } \quad { \text { ( multiply both sides by $ t $ to isolate $ q $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ka\delta t } { d } \quad { \text { ( the time interval is $ 1 \text { hour } $ , which is $ 3600 \text { seconds } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) a\delta t } { d } \quad { \text { ( plug in the $ k $ value for the glass ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) \delta t } { d } \quad { \text { ( the area is $ \text { height } \times \text { width } =0.65\text { m } \times1.25\text { m } =0.8125\text { m } ^2 $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { d } \quad { \text { ( $ \delta t=t_ { hot } -t_ { cold } =20^o\text { c } -5^o\text { c } =15^o\text { c } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { 0.02\text { m } } \quad { \text { ( the thickness $ d $ must be in meters , $ 2\text { cm } =0.02\text { m } $ ) } } $ $ q= 1.84 \times 10^6 \text { j } \quad { \text { ( calculate and celebrate ) } } \quad $
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the cumulative effect from all collisions results in a net flux of heat from the hot body to the colder body . we call this transfer of heat between two objects in contact thermal conduction . image : the molecules in two bodies at different temperatures have different average kinetic energies .
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how do i calculate the heat transfer ?
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what is thermal conduction ? walking on bathroom tile in winter is annoying since it feels so much colder than the carpet . this is interesting , since the carpet and tile are usually both at the same temperature ( i.e . the temperature of the interior of the house ) . the different sensations we feel is explained by the fact that different materials transfer heat at different rates . tile and stone conduct heat more rapidly than carpet and fabrics , so tile and stone feel colder in winter since they transfer heat out of your foot faster than the carpet does . in general , good conductors of electricity ( metals like copper , aluminum , gold , and silver ) are also good heat conductors , whereas insulators of electricity ( wood , plastic , and rubber ) are poor heat conductors . the figure below shows molecules in two bodies at different temperatures . the ( average ) kinetic energy of a molecule in the hot body is higher than in the colder body . if two molecules collide , an energy transfer from the hot to the cold molecule occurs . the cumulative effect from all collisions results in a net flux of heat from the hot body to the colder body . we call this transfer of heat between two objects in contact thermal conduction . image : the molecules in two bodies at different temperatures have different average kinetic energies . collisions occurring at the contact surface tend to transfer energy from high-temperature regions to low-temperature regions . ( image credit : openstax college physics ) what 's the equation for the rate of thermal conduction ? there are four factors ( $ k $ , $ a $ , $ \delta t $ , $ d $ ) that affect the rate at which heat is conducted through a material . these four factors are included in the equation below that was deduced from and is confirmed by experiments . $ \large \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ the letter $ q $ represents the amount of heat transferred in a time $ t $ , $ k $ is the thermal conductivity constant for the material , $ a $ is the cross sectional area of the material transferring heat , $ \delta t $ is the difference in temperature between one side of the material and the other , and $ d $ is the thickness of the material . these factors can be seen visually in the diagram below . image : heat conduction occurs through any material , represented here by a rectangular bar , whether window glass or walrus blubber . ( image credit : openstax college physics ) what does each term represent in the thermal conduction equation ? there 's a lot to digest in the equation for thermal conduction $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ . let 's look at what each factor means individually below . $ \dfrac { q } { t } $ : the factor on the left hand side of the equation $ ( \dfrac { q } { t } ) $ represents the number of $ \text { joules } $ of heat energy transferred through the material per $ \text { second } $ . this means the quantity $ \dfrac { q } { t } $ has units of $ \dfrac { \text { joules } } { \text { second } } =\text { watts } $ . $ k $ : the factor $ k $ is called the thermal conductivity constant . the thermal conductivity constant $ k $ is larger for materials that transfer heat well ( like metal and stone ) , and $ k $ is small for materials that transfer heat poorly ( like air and wood ) . $ \delta t $ : the heat flow is proportional to the temperature difference $ \delta t=t_ { hot } -t_ { cold } $ between one end of the conducting material and the other end . therefore , you will get a more severe burn from boiling water than from hot tap water . conversely , if the temperatures are the same , the net heat transfer rate falls to zero , and equilibrium is achieved . $ a $ : owing to the fact that the number of collisions increases with increasing area , heat conduction depends on the cross-sectional area $ a $ . if you touch a cold wall with your palm , your hand cools faster than if you just touch it with your fingertip . $ d $ : a third factor in the mechanism of conduction is the thickness $ d $ of the material through which heat transfers . the figure above shows a slab of material with different temperatures on either side . suppose that $ t_2 $ is greater than $ t_1 $ , so that heat is transferred from left to right . heat transfer from the left side to the right side is accomplished by a series of molecular collisions . the thicker the material , the more time it takes to transfer the same amount of heat . this model explains why thick clothing is warmer than thin clothing in winters , and why arctic mammals protect themselves with thick blubber . why do metals feel both colder in the winter , and hotter in the summer ? materials with a high thermal conductivity constant $ k $ ( like metals and stones ) will conduct heat well both ways ; into or out of the material . so if your skin comes into contact with metal that is colder than your skin temperature , the metal can rapidly transfer heat energy out of your hand , making the metal feel particularly cold . similarly , if the metal is hotter than your skin temperature , the metal can rapidly transfer heat energy into your hand , making the metal feel particularly hot . this is why concrete will feel especially cold to our bare feet in winter ( the concrete transfers heat out of our feet rapidly ) , and especially hot to our bare feet in summer ( the concrete transfers heat into our feet rapidly ) . what do solved examples involving thermal conduction look like ? example 1 : window makeover a person wants to replace the window on their house , but they do n't want their heating and cooling bills to change . the original window on the wall of the house has area $ a $ , thickness $ d $ , and is made out of glass that has a thermal conduction constant $ k $ . which one of the following changes could be made to the window that would leave the rate of thermal conduction the same as the original window ? ( select one ) example 2 : window heat loss a single-paned window in your house is $ 0.65\text { m } $ wide , $ 1.25\text { m } $ tall , and has a thickness of $ 2\text { cm } $ . the glass has a thermal conduction constant of $ 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } $ . assume the outside temperature of the glass is a constant $ 5^o\text { c } $ and the inside temperature of the glass is a constant $ 20^o\text { c } $ . how many $ \text { joules } $ of heat are transferred out of the window in one hour ? solution : $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } \quad { \text { ( start with the formula for the rate of thermal conduction ) } } $ $ q=\dfrac { tka\delta t } { d } \quad { \text { ( multiply both sides by $ t $ to isolate $ q $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ka\delta t } { d } \quad { \text { ( the time interval is $ 1 \text { hour } $ , which is $ 3600 \text { seconds } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) a\delta t } { d } \quad { \text { ( plug in the $ k $ value for the glass ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) \delta t } { d } \quad { \text { ( the area is $ \text { height } \times \text { width } =0.65\text { m } \times1.25\text { m } =0.8125\text { m } ^2 $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { d } \quad { \text { ( $ \delta t=t_ { hot } -t_ { cold } =20^o\text { c } -5^o\text { c } =15^o\text { c } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { 0.02\text { m } } \quad { \text { ( the thickness $ d $ must be in meters , $ 2\text { cm } =0.02\text { m } $ ) } } $ $ q= 1.84 \times 10^6 \text { j } \quad { \text { ( calculate and celebrate ) } } \quad $
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this means the quantity $ \dfrac { q } { t } $ has units of $ \dfrac { \text { joules } } { \text { second } } =\text { watts } $ . $ k $ : the factor $ k $ is called the thermal conductivity constant . the thermal conductivity constant $ k $ is larger for materials that transfer heat well ( like metal and stone ) , and $ k $ is small for materials that transfer heat poorly ( like air and wood ) .
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how stones with low thermal conductivity are good thermal conductivity ?
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what is thermal conduction ? walking on bathroom tile in winter is annoying since it feels so much colder than the carpet . this is interesting , since the carpet and tile are usually both at the same temperature ( i.e . the temperature of the interior of the house ) . the different sensations we feel is explained by the fact that different materials transfer heat at different rates . tile and stone conduct heat more rapidly than carpet and fabrics , so tile and stone feel colder in winter since they transfer heat out of your foot faster than the carpet does . in general , good conductors of electricity ( metals like copper , aluminum , gold , and silver ) are also good heat conductors , whereas insulators of electricity ( wood , plastic , and rubber ) are poor heat conductors . the figure below shows molecules in two bodies at different temperatures . the ( average ) kinetic energy of a molecule in the hot body is higher than in the colder body . if two molecules collide , an energy transfer from the hot to the cold molecule occurs . the cumulative effect from all collisions results in a net flux of heat from the hot body to the colder body . we call this transfer of heat between two objects in contact thermal conduction . image : the molecules in two bodies at different temperatures have different average kinetic energies . collisions occurring at the contact surface tend to transfer energy from high-temperature regions to low-temperature regions . ( image credit : openstax college physics ) what 's the equation for the rate of thermal conduction ? there are four factors ( $ k $ , $ a $ , $ \delta t $ , $ d $ ) that affect the rate at which heat is conducted through a material . these four factors are included in the equation below that was deduced from and is confirmed by experiments . $ \large \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ the letter $ q $ represents the amount of heat transferred in a time $ t $ , $ k $ is the thermal conductivity constant for the material , $ a $ is the cross sectional area of the material transferring heat , $ \delta t $ is the difference in temperature between one side of the material and the other , and $ d $ is the thickness of the material . these factors can be seen visually in the diagram below . image : heat conduction occurs through any material , represented here by a rectangular bar , whether window glass or walrus blubber . ( image credit : openstax college physics ) what does each term represent in the thermal conduction equation ? there 's a lot to digest in the equation for thermal conduction $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ . let 's look at what each factor means individually below . $ \dfrac { q } { t } $ : the factor on the left hand side of the equation $ ( \dfrac { q } { t } ) $ represents the number of $ \text { joules } $ of heat energy transferred through the material per $ \text { second } $ . this means the quantity $ \dfrac { q } { t } $ has units of $ \dfrac { \text { joules } } { \text { second } } =\text { watts } $ . $ k $ : the factor $ k $ is called the thermal conductivity constant . the thermal conductivity constant $ k $ is larger for materials that transfer heat well ( like metal and stone ) , and $ k $ is small for materials that transfer heat poorly ( like air and wood ) . $ \delta t $ : the heat flow is proportional to the temperature difference $ \delta t=t_ { hot } -t_ { cold } $ between one end of the conducting material and the other end . therefore , you will get a more severe burn from boiling water than from hot tap water . conversely , if the temperatures are the same , the net heat transfer rate falls to zero , and equilibrium is achieved . $ a $ : owing to the fact that the number of collisions increases with increasing area , heat conduction depends on the cross-sectional area $ a $ . if you touch a cold wall with your palm , your hand cools faster than if you just touch it with your fingertip . $ d $ : a third factor in the mechanism of conduction is the thickness $ d $ of the material through which heat transfers . the figure above shows a slab of material with different temperatures on either side . suppose that $ t_2 $ is greater than $ t_1 $ , so that heat is transferred from left to right . heat transfer from the left side to the right side is accomplished by a series of molecular collisions . the thicker the material , the more time it takes to transfer the same amount of heat . this model explains why thick clothing is warmer than thin clothing in winters , and why arctic mammals protect themselves with thick blubber . why do metals feel both colder in the winter , and hotter in the summer ? materials with a high thermal conductivity constant $ k $ ( like metals and stones ) will conduct heat well both ways ; into or out of the material . so if your skin comes into contact with metal that is colder than your skin temperature , the metal can rapidly transfer heat energy out of your hand , making the metal feel particularly cold . similarly , if the metal is hotter than your skin temperature , the metal can rapidly transfer heat energy into your hand , making the metal feel particularly hot . this is why concrete will feel especially cold to our bare feet in winter ( the concrete transfers heat out of our feet rapidly ) , and especially hot to our bare feet in summer ( the concrete transfers heat into our feet rapidly ) . what do solved examples involving thermal conduction look like ? example 1 : window makeover a person wants to replace the window on their house , but they do n't want their heating and cooling bills to change . the original window on the wall of the house has area $ a $ , thickness $ d $ , and is made out of glass that has a thermal conduction constant $ k $ . which one of the following changes could be made to the window that would leave the rate of thermal conduction the same as the original window ? ( select one ) example 2 : window heat loss a single-paned window in your house is $ 0.65\text { m } $ wide , $ 1.25\text { m } $ tall , and has a thickness of $ 2\text { cm } $ . the glass has a thermal conduction constant of $ 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } $ . assume the outside temperature of the glass is a constant $ 5^o\text { c } $ and the inside temperature of the glass is a constant $ 20^o\text { c } $ . how many $ \text { joules } $ of heat are transferred out of the window in one hour ? solution : $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } \quad { \text { ( start with the formula for the rate of thermal conduction ) } } $ $ q=\dfrac { tka\delta t } { d } \quad { \text { ( multiply both sides by $ t $ to isolate $ q $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ka\delta t } { d } \quad { \text { ( the time interval is $ 1 \text { hour } $ , which is $ 3600 \text { seconds } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) a\delta t } { d } \quad { \text { ( plug in the $ k $ value for the glass ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) \delta t } { d } \quad { \text { ( the area is $ \text { height } \times \text { width } =0.65\text { m } \times1.25\text { m } =0.8125\text { m } ^2 $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { d } \quad { \text { ( $ \delta t=t_ { hot } -t_ { cold } =20^o\text { c } -5^o\text { c } =15^o\text { c } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { 0.02\text { m } } \quad { \text { ( the thickness $ d $ must be in meters , $ 2\text { cm } =0.02\text { m } $ ) } } $ $ q= 1.84 \times 10^6 \text { j } \quad { \text { ( calculate and celebrate ) } } \quad $
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this means the quantity $ \dfrac { q } { t } $ has units of $ \dfrac { \text { joules } } { \text { second } } =\text { watts } $ . $ k $ : the factor $ k $ is called the thermal conductivity constant . the thermal conductivity constant $ k $ is larger for materials that transfer heat well ( like metal and stone ) , and $ k $ is small for materials that transfer heat poorly ( like air and wood ) .
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while measuring the thermal conductivity of a liquid why do we keep the upper part hot and the lower cool ?
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what is thermal conduction ? walking on bathroom tile in winter is annoying since it feels so much colder than the carpet . this is interesting , since the carpet and tile are usually both at the same temperature ( i.e . the temperature of the interior of the house ) . the different sensations we feel is explained by the fact that different materials transfer heat at different rates . tile and stone conduct heat more rapidly than carpet and fabrics , so tile and stone feel colder in winter since they transfer heat out of your foot faster than the carpet does . in general , good conductors of electricity ( metals like copper , aluminum , gold , and silver ) are also good heat conductors , whereas insulators of electricity ( wood , plastic , and rubber ) are poor heat conductors . the figure below shows molecules in two bodies at different temperatures . the ( average ) kinetic energy of a molecule in the hot body is higher than in the colder body . if two molecules collide , an energy transfer from the hot to the cold molecule occurs . the cumulative effect from all collisions results in a net flux of heat from the hot body to the colder body . we call this transfer of heat between two objects in contact thermal conduction . image : the molecules in two bodies at different temperatures have different average kinetic energies . collisions occurring at the contact surface tend to transfer energy from high-temperature regions to low-temperature regions . ( image credit : openstax college physics ) what 's the equation for the rate of thermal conduction ? there are four factors ( $ k $ , $ a $ , $ \delta t $ , $ d $ ) that affect the rate at which heat is conducted through a material . these four factors are included in the equation below that was deduced from and is confirmed by experiments . $ \large \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ the letter $ q $ represents the amount of heat transferred in a time $ t $ , $ k $ is the thermal conductivity constant for the material , $ a $ is the cross sectional area of the material transferring heat , $ \delta t $ is the difference in temperature between one side of the material and the other , and $ d $ is the thickness of the material . these factors can be seen visually in the diagram below . image : heat conduction occurs through any material , represented here by a rectangular bar , whether window glass or walrus blubber . ( image credit : openstax college physics ) what does each term represent in the thermal conduction equation ? there 's a lot to digest in the equation for thermal conduction $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } $ . let 's look at what each factor means individually below . $ \dfrac { q } { t } $ : the factor on the left hand side of the equation $ ( \dfrac { q } { t } ) $ represents the number of $ \text { joules } $ of heat energy transferred through the material per $ \text { second } $ . this means the quantity $ \dfrac { q } { t } $ has units of $ \dfrac { \text { joules } } { \text { second } } =\text { watts } $ . $ k $ : the factor $ k $ is called the thermal conductivity constant . the thermal conductivity constant $ k $ is larger for materials that transfer heat well ( like metal and stone ) , and $ k $ is small for materials that transfer heat poorly ( like air and wood ) . $ \delta t $ : the heat flow is proportional to the temperature difference $ \delta t=t_ { hot } -t_ { cold } $ between one end of the conducting material and the other end . therefore , you will get a more severe burn from boiling water than from hot tap water . conversely , if the temperatures are the same , the net heat transfer rate falls to zero , and equilibrium is achieved . $ a $ : owing to the fact that the number of collisions increases with increasing area , heat conduction depends on the cross-sectional area $ a $ . if you touch a cold wall with your palm , your hand cools faster than if you just touch it with your fingertip . $ d $ : a third factor in the mechanism of conduction is the thickness $ d $ of the material through which heat transfers . the figure above shows a slab of material with different temperatures on either side . suppose that $ t_2 $ is greater than $ t_1 $ , so that heat is transferred from left to right . heat transfer from the left side to the right side is accomplished by a series of molecular collisions . the thicker the material , the more time it takes to transfer the same amount of heat . this model explains why thick clothing is warmer than thin clothing in winters , and why arctic mammals protect themselves with thick blubber . why do metals feel both colder in the winter , and hotter in the summer ? materials with a high thermal conductivity constant $ k $ ( like metals and stones ) will conduct heat well both ways ; into or out of the material . so if your skin comes into contact with metal that is colder than your skin temperature , the metal can rapidly transfer heat energy out of your hand , making the metal feel particularly cold . similarly , if the metal is hotter than your skin temperature , the metal can rapidly transfer heat energy into your hand , making the metal feel particularly hot . this is why concrete will feel especially cold to our bare feet in winter ( the concrete transfers heat out of our feet rapidly ) , and especially hot to our bare feet in summer ( the concrete transfers heat into our feet rapidly ) . what do solved examples involving thermal conduction look like ? example 1 : window makeover a person wants to replace the window on their house , but they do n't want their heating and cooling bills to change . the original window on the wall of the house has area $ a $ , thickness $ d $ , and is made out of glass that has a thermal conduction constant $ k $ . which one of the following changes could be made to the window that would leave the rate of thermal conduction the same as the original window ? ( select one ) example 2 : window heat loss a single-paned window in your house is $ 0.65\text { m } $ wide , $ 1.25\text { m } $ tall , and has a thickness of $ 2\text { cm } $ . the glass has a thermal conduction constant of $ 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } $ . assume the outside temperature of the glass is a constant $ 5^o\text { c } $ and the inside temperature of the glass is a constant $ 20^o\text { c } $ . how many $ \text { joules } $ of heat are transferred out of the window in one hour ? solution : $ \dfrac { q } { t } =\dfrac { ka\delta t } { d } \quad { \text { ( start with the formula for the rate of thermal conduction ) } } $ $ q=\dfrac { tka\delta t } { d } \quad { \text { ( multiply both sides by $ t $ to isolate $ q $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ka\delta t } { d } \quad { \text { ( the time interval is $ 1 \text { hour } $ , which is $ 3600 \text { seconds } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) a\delta t } { d } \quad { \text { ( plug in the $ k $ value for the glass ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) \delta t } { d } \quad { \text { ( the area is $ \text { height } \times \text { width } =0.65\text { m } \times1.25\text { m } =0.8125\text { m } ^2 $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { d } \quad { \text { ( $ \delta t=t_ { hot } -t_ { cold } =20^o\text { c } -5^o\text { c } =15^o\text { c } $ ) } } $ $ q=\dfrac { ( 3600\text { s } ) ( 0.84 \dfrac { \text { j } } { \text { s } \cdot \text { m } \cdot ^o\text { c } } ) ( 0.8125 \text { m } ^2 ) ( 15^o\text { c } ) } { 0.02\text { m } } \quad { \text { ( the thickness $ d $ must be in meters , $ 2\text { cm } =0.02\text { m } $ ) } } $ $ q= 1.84 \times 10^6 \text { j } \quad { \text { ( calculate and celebrate ) } } \quad $
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this means the quantity $ \dfrac { q } { t } $ has units of $ \dfrac { \text { joules } } { \text { second } } =\text { watts } $ . $ k $ : the factor $ k $ is called the thermal conductivity constant . the thermal conductivity constant $ k $ is larger for materials that transfer heat well ( like metal and stone ) , and $ k $ is small for materials that transfer heat poorly ( like air and wood ) .
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how does the moisture and alloying of a metal effect its thermal conductivity ?
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who is the central figure in this painting ? the main image in this painting is avalokiteshvara ( 1 ) , the bodhisattva of compassion . he is the principle patron deity of tibet . he sits on a lotus throne upon a lunar disc . this god takes many forms , such as the dalai lamas of tibet , to bring salvation to the living beings of the world . in this painting he has four arms and is white in color . his upper hands hold prayer beads and a lotus ; the lower ones , poised in a hand gesture of prayer , clasp the wish-fulfilling jewel at his heart . this jewel embodies the bodhicitta—the altruistic aspiration to attain highest enlightenment in order to thereby save all beings from misery and establish them in perfect happiness . what is a bodhisattva ? a bodhisattva is a person , either human or divine ( occasionally animal ) who has abandoned all selfish concern and seeks only the ultimate liberation and happiness of all living beings . the bodhisattva understands that as long as he or she remains trapped in the cycle of birth and death ( samsara ) because of greed , anger and ignorance , there is no way that others can truly be helped . therefore , driven by concern for the welfare of others , a bodhisattva pursues the spiritual path to buddhahood , which involves : the perfection of generosity—giving to others with the pure motivation to help them the perfection of morality—avoiding all harm to others , and engaging in activities that benefit others the perfection of patience—never giving way to anger , and accepting the harm perpetrated by others the perfection of effort—persevering with enthusiastic efforts in all virtuous activities the perfection of concentration—training the mind to hold its objects with a calm , clear mind free of all distraction the perfection of wisdom/the realization of ultimate reality—seeing things as they actual are without the overlay of dualistic conceptual processes . in buddhist art , a bodhisattva may appear in divine form wearing crowns and jewels , as an ordinary human , or even as a animal . avalokiteshvara is one of the most popular of the hundreds of bodhisattvas commonly depicted in buddhist art . many , like avalokiteshvara , appear in a variety of distinct forms . what are “ peaceful ” and “ wrathful ” deities ? to those who seek help , both spiritual and mundane , buddhas and bodhisattvas typically appear in peaceful , benevolent forms . to those beings whose minds are set on evil , who stubbornly engage in actions that harm others , the buddhas and bodhisattvas appear in powerful , wrathful forms to subdue them and lead them to virtue . on a psychological level , the wrathful deities represent the powerful , dynamic processes of buddhist meditation that can destroy the underlying causes of all misery—greed , hatred , and delusion , etc . the bodhisattva of compassion is a peaceful deity . he emanates beauty and benevolence . however , in the lower right of the painting is vajrapani ( 4 ) , a wrathful deity , who embodies the sacred power of the buddhas . vajrapani is deep blue in color , has bulging eyes , sharp fangs , fiery hair standing on end , and stands on a golden sun disc . his right hand shoots out in a threatening gesture and wields a vajra . this attribute gives him his name meaning “ vajra in hand. ” vajrapani is a great protector of buddhism . his ferocity is a comfort to believers and terrifying to demons who seek to harm living beings and destroy their paths to salvation . in the lower left of the painting sits manjushri ( 5 ) , the god of supreme wisdom . he holds the book of wisdom and the flaming sword that cuts the roots of ignorance , and severs the sprouts of misery . he is a semi-peaceful deity and sits on a lotus throne on a lunar disc . the three deities togethe —manjushri , avalokiteshvara , and vajrapani—are the three great protectors ( tibetan : rig sum gonpo ) representing wisdom , compassion , and sacred power respectively . who are the green and white taras ? above avalokiteshvara are the green and white taras ( 3 ) , goddesses of compassion and wisdom . white tara has a third eye in the forehead as well as eyes on her palms and feet . green tara , extends her right leg downward . both taras hold the stems of lotuses that blossoms above their shoulders . their right hands are lowered with the palm upward in the gesture of bestowing boons and gifts . the taras are both the objects of prayer and veneration because of their ability to bestow such things as longevity , merit , wisdom , protections from every fear , and spiritual attainments , from the mundane up to supreme enlightenment . the two goddesses have historical significance also . songtsen gampo , the tibetan king who was the first royal patron of buddhism in tibet in the seventh century , married two princesses—bhrikuti , from nepal , and wen cheng from china . these two women helped bring buddhism to tibet , and the nepalese princess introduced the practice of tara to tibet . the two queens are worshiped as manifestations of the green and white taras . who is pictured at the top of this painting ? above the green and white taras are three seated lamas . the central one is tsongkhapa ( 1357–1419 ) ( 6 ) , the founder of the gelukpa order of tibetan buddhism . tsongkhapa is a human disciple of manjushri , and like the god of wisdom pictured below , he has a sword and book supported by lotus blossoms at shoulder level . he is accompanied by his two chief disciples—gyal tsab on his right and khedrup on his left . tsongkhapa ’ s presence in the painting indicates this work belongs to the gelukpa order . what are the objects below the main image ? the group of five objects below the main image is known as the offering of the five senses : the mirror stands for sight , the silk beneath it for touch , the fruit for taste , the conch shell for smell , and the pair of cymbals for sound . this is a typical offering presented to peaceful deities . for wrathful deities , the offering consists of a skullcap heaped with ears , eyeballs , nose , tongue and a heart of demons . paintings like this may have been hung behind the altar in a temple in the home or monastery . real offerings of tea , fruit , flowers , pure water , butter and barley sculptures called torma would be made as well . how is a traditional tibetan thangka mounted ? a tangka is a painting of a buddhist deity , done for religious purposes and made according to strict codes of iconography . a thangka must be framed in silk brocade and consecrated in a ceremony by a qualified lama . it has a pole running across the bottom edge and a cord to hang it at the top . there is usually a yellow silk covering that is hung over the front to provide the deities with privacy . this is folded and draped at the top when on view . this format allows tangkas to be rolled up to be carried from place to place or to be rotated according to annual rituals or festivals . paintings like this traveled easily with traders , itinerant monks , and nomads . learn more on the asian art museum 's education website .
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paintings like this may have been hung behind the altar in a temple in the home or monastery . real offerings of tea , fruit , flowers , pure water , butter and barley sculptures called torma would be made as well . how is a traditional tibetan thangka mounted ?
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would these offerings displayed in the than-khas have some sort of meaning ?
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who is the central figure in this painting ? the main image in this painting is avalokiteshvara ( 1 ) , the bodhisattva of compassion . he is the principle patron deity of tibet . he sits on a lotus throne upon a lunar disc . this god takes many forms , such as the dalai lamas of tibet , to bring salvation to the living beings of the world . in this painting he has four arms and is white in color . his upper hands hold prayer beads and a lotus ; the lower ones , poised in a hand gesture of prayer , clasp the wish-fulfilling jewel at his heart . this jewel embodies the bodhicitta—the altruistic aspiration to attain highest enlightenment in order to thereby save all beings from misery and establish them in perfect happiness . what is a bodhisattva ? a bodhisattva is a person , either human or divine ( occasionally animal ) who has abandoned all selfish concern and seeks only the ultimate liberation and happiness of all living beings . the bodhisattva understands that as long as he or she remains trapped in the cycle of birth and death ( samsara ) because of greed , anger and ignorance , there is no way that others can truly be helped . therefore , driven by concern for the welfare of others , a bodhisattva pursues the spiritual path to buddhahood , which involves : the perfection of generosity—giving to others with the pure motivation to help them the perfection of morality—avoiding all harm to others , and engaging in activities that benefit others the perfection of patience—never giving way to anger , and accepting the harm perpetrated by others the perfection of effort—persevering with enthusiastic efforts in all virtuous activities the perfection of concentration—training the mind to hold its objects with a calm , clear mind free of all distraction the perfection of wisdom/the realization of ultimate reality—seeing things as they actual are without the overlay of dualistic conceptual processes . in buddhist art , a bodhisattva may appear in divine form wearing crowns and jewels , as an ordinary human , or even as a animal . avalokiteshvara is one of the most popular of the hundreds of bodhisattvas commonly depicted in buddhist art . many , like avalokiteshvara , appear in a variety of distinct forms . what are “ peaceful ” and “ wrathful ” deities ? to those who seek help , both spiritual and mundane , buddhas and bodhisattvas typically appear in peaceful , benevolent forms . to those beings whose minds are set on evil , who stubbornly engage in actions that harm others , the buddhas and bodhisattvas appear in powerful , wrathful forms to subdue them and lead them to virtue . on a psychological level , the wrathful deities represent the powerful , dynamic processes of buddhist meditation that can destroy the underlying causes of all misery—greed , hatred , and delusion , etc . the bodhisattva of compassion is a peaceful deity . he emanates beauty and benevolence . however , in the lower right of the painting is vajrapani ( 4 ) , a wrathful deity , who embodies the sacred power of the buddhas . vajrapani is deep blue in color , has bulging eyes , sharp fangs , fiery hair standing on end , and stands on a golden sun disc . his right hand shoots out in a threatening gesture and wields a vajra . this attribute gives him his name meaning “ vajra in hand. ” vajrapani is a great protector of buddhism . his ferocity is a comfort to believers and terrifying to demons who seek to harm living beings and destroy their paths to salvation . in the lower left of the painting sits manjushri ( 5 ) , the god of supreme wisdom . he holds the book of wisdom and the flaming sword that cuts the roots of ignorance , and severs the sprouts of misery . he is a semi-peaceful deity and sits on a lotus throne on a lunar disc . the three deities togethe —manjushri , avalokiteshvara , and vajrapani—are the three great protectors ( tibetan : rig sum gonpo ) representing wisdom , compassion , and sacred power respectively . who are the green and white taras ? above avalokiteshvara are the green and white taras ( 3 ) , goddesses of compassion and wisdom . white tara has a third eye in the forehead as well as eyes on her palms and feet . green tara , extends her right leg downward . both taras hold the stems of lotuses that blossoms above their shoulders . their right hands are lowered with the palm upward in the gesture of bestowing boons and gifts . the taras are both the objects of prayer and veneration because of their ability to bestow such things as longevity , merit , wisdom , protections from every fear , and spiritual attainments , from the mundane up to supreme enlightenment . the two goddesses have historical significance also . songtsen gampo , the tibetan king who was the first royal patron of buddhism in tibet in the seventh century , married two princesses—bhrikuti , from nepal , and wen cheng from china . these two women helped bring buddhism to tibet , and the nepalese princess introduced the practice of tara to tibet . the two queens are worshiped as manifestations of the green and white taras . who is pictured at the top of this painting ? above the green and white taras are three seated lamas . the central one is tsongkhapa ( 1357–1419 ) ( 6 ) , the founder of the gelukpa order of tibetan buddhism . tsongkhapa is a human disciple of manjushri , and like the god of wisdom pictured below , he has a sword and book supported by lotus blossoms at shoulder level . he is accompanied by his two chief disciples—gyal tsab on his right and khedrup on his left . tsongkhapa ’ s presence in the painting indicates this work belongs to the gelukpa order . what are the objects below the main image ? the group of five objects below the main image is known as the offering of the five senses : the mirror stands for sight , the silk beneath it for touch , the fruit for taste , the conch shell for smell , and the pair of cymbals for sound . this is a typical offering presented to peaceful deities . for wrathful deities , the offering consists of a skullcap heaped with ears , eyeballs , nose , tongue and a heart of demons . paintings like this may have been hung behind the altar in a temple in the home or monastery . real offerings of tea , fruit , flowers , pure water , butter and barley sculptures called torma would be made as well . how is a traditional tibetan thangka mounted ? a tangka is a painting of a buddhist deity , done for religious purposes and made according to strict codes of iconography . a thangka must be framed in silk brocade and consecrated in a ceremony by a qualified lama . it has a pole running across the bottom edge and a cord to hang it at the top . there is usually a yellow silk covering that is hung over the front to provide the deities with privacy . this is folded and draped at the top when on view . this format allows tangkas to be rolled up to be carried from place to place or to be rotated according to annual rituals or festivals . paintings like this traveled easily with traders , itinerant monks , and nomads . learn more on the asian art museum 's education website .
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many , like avalokiteshvara , appear in a variety of distinct forms . what are “ peaceful ” and “ wrathful ” deities ? to those who seek help , both spiritual and mundane , buddhas and bodhisattvas typically appear in peaceful , benevolent forms .
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i 've always thought of these as being female deities ( besides the monks ) , is this incorrect ?
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who is the central figure in this painting ? the main image in this painting is avalokiteshvara ( 1 ) , the bodhisattva of compassion . he is the principle patron deity of tibet . he sits on a lotus throne upon a lunar disc . this god takes many forms , such as the dalai lamas of tibet , to bring salvation to the living beings of the world . in this painting he has four arms and is white in color . his upper hands hold prayer beads and a lotus ; the lower ones , poised in a hand gesture of prayer , clasp the wish-fulfilling jewel at his heart . this jewel embodies the bodhicitta—the altruistic aspiration to attain highest enlightenment in order to thereby save all beings from misery and establish them in perfect happiness . what is a bodhisattva ? a bodhisattva is a person , either human or divine ( occasionally animal ) who has abandoned all selfish concern and seeks only the ultimate liberation and happiness of all living beings . the bodhisattva understands that as long as he or she remains trapped in the cycle of birth and death ( samsara ) because of greed , anger and ignorance , there is no way that others can truly be helped . therefore , driven by concern for the welfare of others , a bodhisattva pursues the spiritual path to buddhahood , which involves : the perfection of generosity—giving to others with the pure motivation to help them the perfection of morality—avoiding all harm to others , and engaging in activities that benefit others the perfection of patience—never giving way to anger , and accepting the harm perpetrated by others the perfection of effort—persevering with enthusiastic efforts in all virtuous activities the perfection of concentration—training the mind to hold its objects with a calm , clear mind free of all distraction the perfection of wisdom/the realization of ultimate reality—seeing things as they actual are without the overlay of dualistic conceptual processes . in buddhist art , a bodhisattva may appear in divine form wearing crowns and jewels , as an ordinary human , or even as a animal . avalokiteshvara is one of the most popular of the hundreds of bodhisattvas commonly depicted in buddhist art . many , like avalokiteshvara , appear in a variety of distinct forms . what are “ peaceful ” and “ wrathful ” deities ? to those who seek help , both spiritual and mundane , buddhas and bodhisattvas typically appear in peaceful , benevolent forms . to those beings whose minds are set on evil , who stubbornly engage in actions that harm others , the buddhas and bodhisattvas appear in powerful , wrathful forms to subdue them and lead them to virtue . on a psychological level , the wrathful deities represent the powerful , dynamic processes of buddhist meditation that can destroy the underlying causes of all misery—greed , hatred , and delusion , etc . the bodhisattva of compassion is a peaceful deity . he emanates beauty and benevolence . however , in the lower right of the painting is vajrapani ( 4 ) , a wrathful deity , who embodies the sacred power of the buddhas . vajrapani is deep blue in color , has bulging eyes , sharp fangs , fiery hair standing on end , and stands on a golden sun disc . his right hand shoots out in a threatening gesture and wields a vajra . this attribute gives him his name meaning “ vajra in hand. ” vajrapani is a great protector of buddhism . his ferocity is a comfort to believers and terrifying to demons who seek to harm living beings and destroy their paths to salvation . in the lower left of the painting sits manjushri ( 5 ) , the god of supreme wisdom . he holds the book of wisdom and the flaming sword that cuts the roots of ignorance , and severs the sprouts of misery . he is a semi-peaceful deity and sits on a lotus throne on a lunar disc . the three deities togethe —manjushri , avalokiteshvara , and vajrapani—are the three great protectors ( tibetan : rig sum gonpo ) representing wisdom , compassion , and sacred power respectively . who are the green and white taras ? above avalokiteshvara are the green and white taras ( 3 ) , goddesses of compassion and wisdom . white tara has a third eye in the forehead as well as eyes on her palms and feet . green tara , extends her right leg downward . both taras hold the stems of lotuses that blossoms above their shoulders . their right hands are lowered with the palm upward in the gesture of bestowing boons and gifts . the taras are both the objects of prayer and veneration because of their ability to bestow such things as longevity , merit , wisdom , protections from every fear , and spiritual attainments , from the mundane up to supreme enlightenment . the two goddesses have historical significance also . songtsen gampo , the tibetan king who was the first royal patron of buddhism in tibet in the seventh century , married two princesses—bhrikuti , from nepal , and wen cheng from china . these two women helped bring buddhism to tibet , and the nepalese princess introduced the practice of tara to tibet . the two queens are worshiped as manifestations of the green and white taras . who is pictured at the top of this painting ? above the green and white taras are three seated lamas . the central one is tsongkhapa ( 1357–1419 ) ( 6 ) , the founder of the gelukpa order of tibetan buddhism . tsongkhapa is a human disciple of manjushri , and like the god of wisdom pictured below , he has a sword and book supported by lotus blossoms at shoulder level . he is accompanied by his two chief disciples—gyal tsab on his right and khedrup on his left . tsongkhapa ’ s presence in the painting indicates this work belongs to the gelukpa order . what are the objects below the main image ? the group of five objects below the main image is known as the offering of the five senses : the mirror stands for sight , the silk beneath it for touch , the fruit for taste , the conch shell for smell , and the pair of cymbals for sound . this is a typical offering presented to peaceful deities . for wrathful deities , the offering consists of a skullcap heaped with ears , eyeballs , nose , tongue and a heart of demons . paintings like this may have been hung behind the altar in a temple in the home or monastery . real offerings of tea , fruit , flowers , pure water , butter and barley sculptures called torma would be made as well . how is a traditional tibetan thangka mounted ? a tangka is a painting of a buddhist deity , done for religious purposes and made according to strict codes of iconography . a thangka must be framed in silk brocade and consecrated in a ceremony by a qualified lama . it has a pole running across the bottom edge and a cord to hang it at the top . there is usually a yellow silk covering that is hung over the front to provide the deities with privacy . this is folded and draped at the top when on view . this format allows tangkas to be rolled up to be carried from place to place or to be rotated according to annual rituals or festivals . paintings like this traveled easily with traders , itinerant monks , and nomads . learn more on the asian art museum 's education website .
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in buddhist art , a bodhisattva may appear in divine form wearing crowns and jewels , as an ordinary human , or even as a animal . avalokiteshvara is one of the most popular of the hundreds of bodhisattvas commonly depicted in buddhist art . many , like avalokiteshvara , appear in a variety of distinct forms .
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also what is the difference between a four armed tara and avalokiteshvara as depicted ?
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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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how does the nucleus get its double membrane ( since the theory for how mitochondria gets it is the endosymbiosis theory ) ?
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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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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 .
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does the perinuclear area serve any other function other than protecting the 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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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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why are cells so microscopic ?
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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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what is the biological process by which the endoplasmic reticuli synthesize their products ?
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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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and how does the addition of ribosomes in the endoplasmic reticulum affect that process ?
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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 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 .
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is there any evidence of a type of organelle that used to exist but does n't anymore due to the organism evolving to where it no longer needs 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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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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what keeps the nucleoplasm from coming out of the nuclear pores ?
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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 can lysosomes not operate with the cell 's internal ph of 7 ?
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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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how are microfilaments and intermediate filaments different ?
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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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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 .
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why do mitochondrion have their own set of 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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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 are other major difference between prokaryotic cells and eukaryotic 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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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 .
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in a plant cell , how are mitochondria used if they have chloroplasts ?
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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 difference between the cytoskeleton and the cell wall/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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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 .
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what determines if a protein is sent there by mistake ?
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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 determine where to send each protein ?
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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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are all proteins made with the same structure ?
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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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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 .
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is there a difference between dna found in the mitochondria opposed to the dna found in thee nucleus 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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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 .
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what is the difference in functions 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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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 each of the organelles formed ?
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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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for instance , how does the membrane form ?
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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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is there any organelle that a cell would be able to survive without ?
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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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how does the smooth er detoxify 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 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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in the nucleus when the dna is turned into protein , what is the difference between the processes of transcription and translation ?
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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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in a cell , why is there more than one cell 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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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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in the nucleolus paragraph , why is a nucleolus not 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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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 types of foods have antioxidants in 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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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 .
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if the nucleolus has a function of making ribosomes , why is it not considered 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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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 .
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humans have no need for their appendix anymore due to evolution , so could something be missing a kind of organelle and still function as normal ?
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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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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 .
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if not , is there a possibility of evolution where we wo n't need a type of organelle in the future ?
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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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at one point , would n't a lysosome have to break its self down ?
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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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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 .
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why do plant cells have a mitochondria and chloroplast if they do 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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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 ) .
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in the bullet list , how do vesicles get a special chemical signal to approve their transport out 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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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 golgi complex also direct fatty acids to peroxisomes for decomposition ?
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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 .
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in the er paragraph , what exactly is the lumen and what is it used for ?
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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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also , in the paragraph about plants and platelets paragraph , are platelets actually cells if they have no dna and no 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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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 does a cell have to 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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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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where does the part of the broken down substances that the cell does not use go ?
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