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of Contents Microfilaments Of the three types of protein fibers, microfilaments are the narrowest. Microfilaments are composed of two intertwined strands of actin. They function in cellular movement and have a diameter of about 7 nm. Microfilaments also provide some rigidity and help form the shape of the cell. They c... |
ends of the cell. (Figure 4.16). Figure 4.16 (a) A centrosome is composed of two centrioles positioned at right angles to each other. (b) In animal cells, the centrosomes (arrows) serve as microtubule-organizing centers of the mitotic spindle during mitosis. (credit: Parker et al. / Microbiology OpenStax) 116 Return t... |
d. centrosomes 2. Which type of lipid forms the base structure of the plasma membrane? a. fats b. phospholipids c. oils d. wax 3. Describe the parts of the cytoplasm. Answers 1. (c) 2. (b) 3. The cytoplasm is made up of two parts: the cytosol and the cytoskeleton. The cytosol contains organelles, cytoskeleton, and var... |
bound nucleus and numerous membrane-bound organelles. Such organelles include the endoplasmic reticulum, Golgi apparatus, chloroplasts, mitochondria, and others (Figure 4.18). The word “organelle” means “little organ” and organelles have specialized cellular functions just as your body's organs have specialized functio... |
osomes, found in the nucleus, contain the cell’s genetic information. They are composed of DNA wound around proteins (Figure 4.21). Together, this combination of DNA and proteins is called chromatin (Figure 4.21). When cells are not dividing, individual chromosomes are not visible, and the material in the nucleus is re... |
. (c) Smooth ER (source: mouse tissue). EM × 110,510. (Micrographs provided by the Regents of University of Michigan Medical School © 2012 / Anatomy of Physiology OpenStax) The hollow portion of the ER tubules is called the lumen or cisternal space. The membrane of the ER, which is a phospholipid bilayer embedded with ... |
failure can occur when cardiac muscle cells' endoplasmic reticula do not function properly. As a result, an insufficient number of calcium ions are available to trigger a sufficient contractile force. Cardiologists (cardi- = “heart”; -ologist = “one who studies”) are doctors who specialize in treating heart diseases. ... |
icles deposit their contents into other parts of the cell, other vesicles fuse with the plasma membrane and release their contents outside the cell. 126 Return to Table of Contents The quantity of Golgi varies in different cells. Cells that are involved in secreting large quantities of materials have higher amounts of ... |
.24 A macrophage has taken up a bacterium, which then fuses with a lysosome within the cell. Other organelles are present in the cell, but for simplicity, are not shown. (credit: Modified by Elizabeth O’Grady original work by Clark et al. / Biology 2E OpenStax) Access for free at https://openstax.org/ 127 Vesicles and ... |
(Figure 4.26) that have their own ribosomes and DNA. Each membrane is a phospholipid bilayer embedded with proteins. The inner layer has folds called cristae, which increase the surface area of the inner membrane. The area surrounded by the folds is called the inner mitochondrial matrix (space). The space between the ... |
ochondria perform cellular respiration and produce ATP. Peroxisomes break down fatty acids, amino acids, and some toxins. Vesicles and vacuoles are storage and transport compartments. In plant cells, vacuoles also help break down macromolecules. Exercises 1. Which of the following organelles is most likely to aid in th... |
asmic reticulum (ER): a series of interconnected membranous structures within eukaryotic cells that collectively modify proteins and synthesize lipids Golgi apparatus: a eukaryotic organelle made up of a series of stacked membranes that sorts, tags, and packages lipids and proteins for distribution lysosome: an organel... |
material, and use ribosomes to synthesize proteins. Despite their fundamental similarities, there are some striking differences amongst the different groups of cells that make up the eukaryotes. Those groups being Plantae, Protista, Animalia, and Fungi. We will briefly introduce the groups Protista and Fungi, before f... |
cells have a cell wall, chloroplasts, and a large central vacuole. Plant cells also have plastids that are used for storage. For example, cells that make up the potato have amyloplasts, a type of plastid used for storing starch. These organelles are not found in animal cells. As you learned in previous sections, anima... |
of Biology OpenStax). The chloroplasts contain a green pigment called chlorophyll, which captures the energy of sunlight for photosynthesis. It is this pigment that gives leaves their green appearance. Like plant cells, photosynthetic protists also have chloroplasts. Some bacteria also perform photosynthesis, but they... |
occurred. Figure 4.30 The first eukaryote may have originated from an ancestral prokaryote that had undergone membrane proliferation, compartmentalization of cellular function (into a nucleus, lysosomes, and an endoplasmic reticulum), and the establishment of endosymbiotic relationships with an aerobic prokaryote. (cr... |
tight junctions, gap junctions, and desmosomes, a type of anchoring junction (Figure 4.32). Figure 4.32 There are four kinds of connections between cells. (a) plasmodesma (b) Tight junctions (c) Desmosomes (d) Gap junctions (credit b, c, d: modification of work by Mariana Ruiz Villareal / Concepts of Biology OpenStax)... |
2E OpenStax) Access for free at https://openstax.org/ 139 Gap junctions Gap junctions in animal cells are like plasmodesmata in plant cells. They are channels between adjacent cells that allow for the transport of ions, nutrients, and other substances that enable cells to communicate (Figure 4.36). These junctions all... |
role in cell division in animal cells; organizing center of microtubules in animal cells No Lysosomes Digestion of macromolecules; recycling of worn-out organelles No Yes Yes No No Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes Yes No Yes No Cell wall Protection, structural support, and maintenance of cell shape Yes, primari... |
and gap junctions. Exercises 1. What structures does a plant cell have that an animal cell does not have? What structures does an animal cell have that a plant cell does not have? 2. Which two organelles are thought to have once been free-living bacteria? 3. In plant cells, the cell wall has a large abundance of what ... |
and anchoring for cells in the tissue gap junction: a channel between two adjacent animal cells that allows ions, nutrients, and other low-molecular-weight substances to pass between the cells, enabling the cells to communicate heterotroph: an organism that cannot make its own food and must consume other organisms to ... |
explained the function of the plasma membrane. The fluid mosaic model has evolved somewhat over time, but it still best accounts for plasma membrane structure and function as we currently understand them. The fluid mosaic model describes the plasma membrane as a mosaic of components, including phospholipids, cholester... |
id molecule. (credit: Clark et al. / Biology 2E OpenStax) Proteins The lipid bilayer forms the basis of the cell membrane; however, there are various proteins peppered throughout. Membrane proteins are categorized as either integral proteins or peripheral proteins (Figure 5.2). As its name suggests, an integral protein... |
in a person’s body are a result of that person’s genetic makeup. They help identify cells as belonging to the same individual. This identity is the primary way that a person’s immune defense cells “know” not to attack the person’s own body cells. It is also the reason organs donated by another person might be rejected... |
. Viruses appear to be incredibly adaptable, and the rate at which populations are evolving is astounding. A person infected with HIV quickly develops different populations of the virus that vary in their surface markers. Although the immune system may be able to fight one population, as new populations arise it become... |
mosaic of components, including phospholipids, cholesterol, proteins, and glycolipids, resulting in a fluid rather than static character glycocalyx: a fuzzy-appearing coating around the cell formed from glycoproteins and other carbohydrates attached to the cell membrane. glycolipid: a combination of carbohydrates and ... |
energy. In contrast, active transport is the movement of materials across the membrane using energy, usually in the form of ATP. Passive Transport The most direct forms of membrane transport are passive. Passive transport occurs naturally and does not require the cell to expend energy to accomplish the movement. To un... |
5.8). Access for free at https://openstax.org/ 153 Figure 5.7 Diffusion of molecules through a permeable membrane. (credit: modification of work by Mariana Ruiz Villareal / Microbiology OpenStax) Each separate substance in an environment has its own concentration gradient, independent of the concentration gradients of... |
on the exterior surface of the plasma membrane. This allows the material that is needed by the cell to be removed from the extracellular fluid or cytoplasm. The substances are then passed to specific integral proteins that facilitate their passage. Integral proteins form channels or pores that allow certain materials ... |
of low free water concentration until equilibrium is met. Figure 5.10 In osmosis water always moves through a semipermeable membrane from an area of low solute concentration to an area of higher solute concentration. (credit: Fowler et al. / Concepts of Biology OpenStax) 156 Return to Table of Contents Tonicity Tonici... |
ax) Access for free at https://openstax.org/ 157 No, the solution injected was most likely a hypotonic solution, such as distilled water. This resulted in the blood being hypotonic when compared to the cytoplasm of the cells. Water moved into the cells from an area of low solutes in the blood to an area of high solutes... |
through protein channels or by slipping between the lipid tails of the membrane itself. Osmosis is the movement of water molecules through a semipermeable membrane from an area of low solute concentration to an area of high solute concentration. Two solutions that have the same concentration of solutes are said to be ... |
cell that requires energy concentration gradient: an area of high concentration across from an area of low concentration diffusion: a passive process of transport where solutes move from an area of high concentration to an area of low concentration until equilibrium is met facilitated transport: a process by which sol... |
membrane proteins to transport substances such as molecules or ions across the membrane. For example, some cells have a high concentration of potassium (K+) and a low concentration of sodium (Na+) inside the cell when compared to that of the extracellular fluid. The sodiumpotassium pump transports sodium out of a cell... |
cell called a neutrophil removes the invader through this process of phagocytosis. The neutrophil surrounds and engulfs the microorganism (Figure 5.15a). The microorganism, which is now contained in a vacuole, will fuse with a lysosome and be destroyed by the digestive enzymes. Pinocytosis Another variation of endocyt... |
the material either into or out of the cell against their concentration gradients. One of the most common types of active transport involves proteins that serve as pumps. Endocytosis is a type of active transport that moves large molecules into the cell. These large molecules, which can include cell parts and foreign ... |
indirectly from the sun. Producers, such as plants, can directly capture sunlight and convert it into chemical energy, such as glucose. Because producers make their own food, they are considered autotrophs. Herbivores, carnivores, and omnivores are classified as consumers because they must obtain their chemical energy... |
used to form adenosine triphosphate (ATP) through a process called cellular respiration. Adenosine triphosphate (ATP) is the primary energy currency of all living cells. Cellular respiration is a metabolic pathway that is basically the reverse reaction of photosynthesis. The reaction is summarized as: C6H12O6 + 6O2 --... |
cell (Figure 5.21). Both anabolism and catabolism occur simultaneously and continuously within cells. These metabolic reactions allow cells to maintain homeostasis. The chemical reactions that make up metabolic pathways do not take place on their own. Each reaction is facilitated, or catalyzed, by a protein called an ... |
P): is the primary energy currency of all living cells anabolic: describes the pathway that requires a net energy input to synthesize complex molecules from simpler ones catabolic: describes the pathway in which complex molecules are broken down into simpler ones, yielding energy as an additional product of the reactio... |
bikes”: modification of work by Michelle Riggen-Ransom; credit “leaf”: modification of work by Cory Zanker / Biology 2E OpenStax) It may seem easy for living cells to obtain, transform, and use energy to do work; however, this is not the case. Energy transfers and transformations are never completely efficient. In eve... |
molecules diffuse. (credit: Modified by Elizabeth O'Grady original work of Robby Remedi) Living organisms are highly ordered. Organisms require a constant input of energy to maintain this state of low entropy. As living organisms take in energy and transform it through chemical reactions, some amount of usable energy ... |
Think of a wrecking ball. Even a slow-moving wrecking ball can do a great deal of damage to other objects. The energy associated with objects in motion is called kinetic energy. A speeding bullet, a person walking, and flowing water all have kinetic energy (Figure 5.26). Figure 5.26 Still water has potential energy; m... |
The type of potential energy that exists within chemical bonds is called chemical energy. CONCEPTS IN ACTION- Visit the site and select “Pendulum” from the “Work and Energy” menu to see the shifting kinetic and potential energy of a pendulum in motion. 176 Return to Table of Contents Free and Activation Energy Accordi... |
burst of energy is released. That energy can be harnessed to perform cellular work. ATP can be thought of as the primary energy currency of living cells. ATP provides the energy used to power the majority of cellular chemical reactions and processes that occur in the cell. The energy from ATP drives all bodily functio... |
energy released by ATP perform work inside the cell? This depends on a strategy referred to as energy coupling. Cells couple exergonic processes that release energy with those endergonic processes that require energy. In Figure 5.34, this sodium-potassium pump drives sodium out of the cell and potassium into the cell ... |
All the above are examples of energy transformations 3. Which of the following is not true about ATP? a. It is the primary energy currency of all living cells. b. The phosphate-phosphate bonds represent large amounts of kinetic energy c. Phosphate-phosphate bonds repel one another and make the molecule unstable d. ATP... |
chemical reaction to occur. (a) Without an enzyme, the energy input needed for a reaction to begin is high. (b) With the help of an enzyme, less energy is needed for a reaction to begin. (credit: Betts et al. / Anatomy and Physiology OpenStax) 184 Return to Table of Contents Enzymes speed up the rate of chemical react... |
to work best under certain optimal conditions. Changes in pH and salt concentration range, as with temperature, can cause enzymes to denature. Figure 5.38 The induced-fit model explains how enzymes and substrates undergo dynamic modifications during the transition state to increase the affinity of the substrate for th... |
compared to normal enzyme activity. Figure 5.39 This plot shows the rate of reaction versus substrate concentration for an enzyme in the absence of the inhibitor and the enzyme in the presence of competitive and non-competitive inhibitors. (credit: Clark et al. / Biology 2E OpenStax) Non-competitive inhibition In non-... |
enzymes. Cofactors are inorganic ions such as iron and magnesium, whereas coenzymes are organic helper molecules. Like enzymes, these molecules participate in reactions without being altered and can be reused. Vitamins are a source of coenzymes (Figure 5.42). Vitamin C is a coenzyme for enzymes used to synthesize the i... |
the square hole and a round peg fitting through the round hole of a children’s toy d. the fitting together of two jigsaw puzzle pieces 2. An allosteric inhibitor: a. Binds to the enzyme in a location other than the active site, increasing its affinity for substrate binding. b. Binds to the active site and blocks it fr... |
binding, thus inhibiting the overall rate of reaction for the enzyme denature: loss of shape in a protein that may be a result of changes in temperature, pH, or chemical exposure enzyme: a molecule that catalyzes a biochemical reaction feedback inhibition: a mechanism of enzyme activity regulation in which the product... |
from glucose is used to drive the synthesis of ATP with the help of oxygen. During the process, both carbon dioxide and water are released as waste products. In addition, like all energy transformations, some energy is lost in the form of heat. Aerobic cellular respiration can be summarized by the equation below: Figu... |
atom's potential energy is found in the form of its high-energy electrons. The transfer of electrons between atoms allows the cell to transfer and use energy in small increments rather than a single, destructive burst. Section 6.2 will focus on how energy is extracted from glucose in small increments to generate ATP. ... |
196 Return to Table of Contents ATP in Living Systems ATP is often called the “energy currency" of a cell because it provides much of the energy needed to carry out cellular processes. ATP is classified as a high energy molecule because the covalent bonds that link the phosphate groups contain large quantities of pote... |
made during glucose catabolism. It is also used in photosynthesis to convert light energy from the sun to chemical energy found in the bonds of ATP. Chemiosmosis yields ATP as long as oxygen is present. The details of oxidative phosphorylation will be discussed in section 6.4. Figure 6.9 In eukaryotes, oxidative phosp... |
high-energy phosphate to a compound, usually a metabolic intermediate, a protein, or ADP redox reaction: a chemical reaction that consists of the coupling of an oxidation reaction and a reduction reaction reduction reaction: a chemical reaction that consists of an electron being gained by an atom substrate-level phosp... |
the words pyruvate and pyruvic acid interchangeably. Recall that two ATP molecules were invested in the first phase of glycolysis, therefore one glucose molecule results in a net production of two ATP molecules. Figure 6.11 shows an overview of glycolysis. (credit: Betts et al. / Anatomy and Physiology OpenStax) 202 R... |
the pathway, the cell has a net gain of two ATP molecules. Figure 6.14 shows the inputs and outputs of glycolysis. (credit: Jason Cashmore) Answer: 8 204 Return to Table of Contents Section Summary Glycolysis is the first pathway used in the breakdown of glucose. Because nearly all organisms on earth use it, glycolysi... |
openstax.org/ 205 6.3 Citric Acid Cycle In eukaryotic cells, the pyruvate molecules produced at the end of glycolysis are transported into mitochondria. If oxygen is available, aerobic cellular respiration will go forward. Pyruvate Oxidation In the mitochondria, pyruvate will be oxidized into a two-carbon acetyl group.... |
entered into glycolysis, two molecules of acetyl CoA can be formed. As a result, the citric acid cycle can make two turns for every one molecule of glucose, forming a total of four carbon dioxide, two ATP (or an equivalent), six NADH, and two FADH2 molecules. The six NADH and two FADH2 are electron carriers that will ... |
. They go on to the electron transport chain. c. They energize the entry of the acetyl group into the citric acid cycle. d. They are converted into NADP. 2. In eukaryotic cells, where does pyruvate oxidation occur? a. mitochondria b. cytoplasm c. nucleus d. plasma membrane 3. If a cell has access to three molecules of ... |
stair energy are given off, which can be used to generate ATP. (credit: Modified by Elizabeth O'Grady original work of Betts et al. / Anatomy and Physiology OpenStax) As electrons are passed rapidly from one protein to the next in a series of redox reactions, some energy is released. At the end of the protein chain, o... |
chain. Access for free at https://openstax.org/ 211 Chemiosmosis As electrons are passed through the electron transport chain, the energy released is used to establish a hydrogen ion concentration gradient. Because of their charge, hydrogen ions can only diffuse across the inner membrane of the mitochondria through in... |
FADH2, in contrast, delivers its electrons to protein complex II and they only travel through part of the transport chain. When accounting for the total number of ATP produced per glucose molecule, it is important to remember the following points: • A net of two ATP is produced through glycolysis (four produced, but t... |
. 2. What happens to NADH when it arrives at the electron transport chain? a. It is reduced to NAD+ b. It is oxidized to NAD+ c. It is reduced to FAD d. It is oxidized to FAD 3. Chemiosmosis in eukaryotic cells involves: a. the movement of electrons across the cell membrane b. the movement of hydrogen atoms across the ... |
organisms are able to use an organic molecule as the final electron acceptor in times when oxygen levels are low or absent. Processes that use an organic molecule to regenerate NAD+ from NADH are collectively referred to as fermentation. In contrast, some living systems use an inorganic molecule as a final electron ac... |
. Ethanol above 12 percent is toxic to yeast, so natural levels of alcohol in wine occur at a maximum of 12 percent. Figure 6.26 The fermentation of grape juice to make wine produces CO2 as a byproduct. Fermentation tanks have valves so that pressure inside the tanks can be released. (credit: Clark et al. / Biology 2E ... |
lation. Exercises 1. True or False: Lactic acid can be converted back to pyruvate. 2. Which of the following fermentation methods can occur in animal skeletal muscles? a. lactic acid fermentation b. alcohol fermentation c. mixed acid fermentation d. propionic fermentation 3. When muscle cells run out of oxygen, what ha... |
. Both sugars must be hydrolyzed before they can be utilized. Sucrose, commonly referred to as table sugar, is broken down into glucose and fructose with the help of the enzyme sucrase. Lactose, a sugar found in milk, is hydrolyzed into glucose and galactose with the help of the enzyme lactase. Both fructose and galact... |
Summary The breakdown and synthesis of carbohydrates, proteins, and lipids can be used to generate ATP. Galactose and fructose are additional carbohydrates that can feed into glycolysis. The amino acids from proteins can be used to generate pyruvate, acetyl CoA, and components of the citric acid cycle. Cholesterol, gl... |
. A third group of bacteria synthesizes sugars, but not by using light energy. These organisms extract energy from inorganic chemical compounds and are referred to as chemoautotrophs. Access for free at https://openstax.org/ 223 Figure 7.2 Photoautotrophs including (a) plants, (b) algae, and (c) cyanobacteria synthesiz... |
ady original pictures by: wolf - Mas3cf / deer - modification of work by Steve VanRiper / plant - Katpatuka /sun - NASA/SDO) CONCEPTS IN ACTION- Click the following link to learn more about photosynthesis. Access for free at https://openstax.org/ 225 Main Structures and Summary of Photosynthesis Photosynthesis is a mul... |
, plants take in carbon dioxide and release oxygen. Gas exchange into and out of the leaf occurs through small openings called stomata (singular: stoma). Stomata play roles in both the regulation of gas exchange and water balance. The stomata are typically located on the underside of the leaf, which helps to minimize w... |
.9). The light-dependent reactions take place in the thylakoid membrane, where chlorophyll absorbs light energy and then converts it into chemical energy with the help of water. In the light-dependent reactions water is broken down, and oxygen is released as a byproduct. The Calvin cycle takes place in the stroma. Duri... |
membranes. c. The space surrounding thylakoids is called stroma. d. Thylakoids contain pigments such as chlorophyll. 4. Heterotrophs directly obtain their energy from: a. the sun b. the sun and eating other organisms c. eating other organisms d. consuming water 5. Why are carnivores, such as lions, dependent on photos... |
roma: the fluid-filled space surrounding the grana inside a chloroplast where the Calvin cycle reactions of photosynthesis take place thylakoid: a disc-shaped membranous structure inside a chloroplast where the light-dependent reactions of photosynthesis take place using chlorophyll embedded in the membranes Access for... |
them. Keep in mind that living organisms cannot utilize all parts of the electromagnetic spectrum. For example, high-energy waves are dangerous to living organisms. Exposure to large quantities of X-rays and UV rays can be harmful to humans and have been identified as causes of cancer. Figure 7.12 The sun emits energy... |
7.14 Plants that commonly grow in the shade benefit from having a variety of light-absorbing pigments. (credit: Jason Hollinger / Concepts of Biology OpenStax) How Light-Dependent Reactions Work The overall purpose of the light-dependent reactions is to convert light energy into chemical energy in the form of ATP and ... |
openstax.org/ 235 Light energy causes an electron in the reaction center chlorophyll a molecules to become “excited" (Figure 7.17). As the electron is excited, the energy associated with the electron increases. In the excited state, the electron is donated by the chlorophyll a molecules and passed to the primary electr... |
ylakoid space. The oxygen molecules are released to the surrounding environment, and the hydrogen ions become part of the hydrogen ion gradient, which is used to generate ATP. The light-dependent reactions are necessary because they provide energy in the form of ATP and NADPH to generate sugar. ATP and NADPH carry ener... |
5. Describe the pathway of energy in light-dependent reactions. 238 Return to Table of Contents Answers 1. (b) 2. (c) 3. (a) 4. (b) 5. The energy is present initially as light. A photon of light hits chlorophyll, causing an electron to be energized. The free-electron travels through the electron transport chain, and t... |
inning American scientist Melvin Calvin, who discovered them. Figure 7.20 Light-dependent reactions harness energy from the sun to produce ATP and NADPH. These energy-carrying molecules travel into the stroma where the Calvin cycle reactions take place. (credit: Fowler et al. / Concepts of Biology OpenStax) The Calvin ... |
and NADPH are generated in the thylakoid membrane through the light-dependent reactions (Figure 7.23). The Calvin cycle occurs in the stroma and begins when carbon dioxide is fixed to RuBP with the help of the enzyme rubisco. For one turn of the Calvin cycle, the plant cell gets to use one G3P to synthesize carbohydra... |
. (credit: Elizabeth O'Grady) Drought-adapted plants have evolved in such a way that they are able to reduce the impact of photorespiration. C4 plants, such as corn and sugar cane, can photosynthesize even when CO2 is in short supply. When it is extremely hot and dry, plants are forced to close most or all of their sto... |
in the chloroplast. The Calvin cycle needs 18 ATP and the electrons carried by 12 NADPH from the light dependent reactions to fix the 6 CO2 into 2 G3P. Access for free at https://openstax.org/ 245 Section Summary Using the energy carriers formed in the first stage of photosynthesis, the Calvin cycle reactions fix CO2 ... |
will fix oxygen to RuBP 246 Return to Table of Contents Chapter 8: Introduction to Reproduction at the Cellular Level Figure 8.1 A sea urchin begins life as a single cell that (a) divides to form two cells, visible by scanning electron microscopy. After four rounds of cell division, (b) there are 16 cells, as seen in ... |
karyotes also have smaller loops of DNA called plasmids. Plasmids are not essential for normal growth, but often contain unique genes that confer beneficial properties, such as antibiotic resistance. These plasmids can be exchanged between different bacteria, and therefore, the beneficial properties can propagate. Figu... |
249 Figure 8.4 From top to bottom: The top panel shows a DNA double helix. The second panel shows the double helix wrapped around histone proteins, which makes a nucleosome. The middle panel shows multiple nucleosomes. The fourth panel shows that the chromatin fiber further condenses into the chromosome shown in the b... |
completing the process of meiosis. Meiosis is a process that produces specialized reproductive cells called eggs and sperm (Figure 8.5). Sexual reproduction requires the egg and sperm to come together to form a fertilized egg, also called a zygote. In humans, gametes are produced in the testes of males and the ovaries... |
chromosomes are in a semi-condensed state, meaning chromatin is visible; however, individual chromosomes are not. In the S phase or synthesis phase, DNA replication occurs. DNA replication involves making an identical copy of each chromosome. It is helpful to refer to chromosomes as being in either the unduplicated st... |
growth during G2. The final preparations for the mitotic phase must be completed before the cell can enter the first stage of mitosis. G0 Phase Some cells can also enter a resting phase called the G0 phase (Figure 8.10). Cells, such as muscle cells and hair follicle cells, can temporarily stop dividing and will not en... |
duplicated state to be divide. During this phase, the nuclear envelope starts to breakdown into small vesicles. The Golgi apparatus and endoplasmic reticulum fragment and disperse to the outer edges of the cell, and the nucleolus disappears. The centrosomes begin to move to opposite poles of the cell with the help of ... |
tokinesis Cytokinesis is the second part of the mitotic phase. During cytokinesis, cell division is completed when the cytoplasmic components are physically separated into two identical daughter cells. Although the stages of mitosis are similar for most eukaryotes, the process of cytokinesis is very different for eukar... |
cycle varies greatly depending on the organism. Even within a multicellular organism, not all cells will divide at the same rate. In humans, the frequency of cell division ranges from embryonic cells that divide in just a few hours to cells like the neurons of the brain that never divide. There is also variation in th... |
ase is an irreversible step, the cycle will not proceed until each pair of sister chromatids is firmly anchored to spindle fibers arising from opposite poles of the cell. 260 Return to Table of Contents CONCEPTS IN ACTION- Watch what occurs at the G1, G2, and M checkpoints by visiting this animation of the cell cycle. ... |
limitations. Depending on a tumor’s location surgeons may be unable to remove it. Radiation and chemotherapy are difficult, and it is often impossible to target only the cancer cells. The treatments inevitably destroy healthy tissue, as well. To address this, researchers are working on pharmaceuticals that can target ... |
. (b) 3. (c) 4. (a) 5. (c) 6. There are very few similarities between animal cell and plant cell cytokinesis. In animal cells, a ring of actin fibers is formed around the periphery of the cell at the former metaphase plate. The actin ring contracts inward, pulling the plasma membrane toward the center of the cell until... |
ore: a protein structure in the centromere of each sister chromatid that attracts and binds spindle microtubules during prometaphase metaphase plate: the equatorial plane midway between two poles of a cell where the chromosomes align during metaphase Access for free at https://openstax.org/ 263 metaphase: the stage of ... |
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