Answers to Chapter Eight

ANSWERS TO CHAPTER EIGHT

1. Answer: b. Most prokaryotic genes are circular without a nucleus, although plasmids can exist. 2. Answer: a. The prokaryotic genes are usually negatively supercoiled, against the grain of the double helix. There are no histone or non-histone proteins involved. 3. Answer: a. The promotor sequence binds selectively to the RNA polymerase enzyme so that transcription can take place under the right circumstances. 4. Answer: b. These parts of a eukaryotic cell all contain individual DNA molecules. The eukaryotic cell does not have a nucleoid so there is no

“nucleoid DNA” in a eukaryotic cell. 5. Answer: d. Luteinizing hormone is protein-based so it does not enter the nucleus. The others are steroid hormones that can enter the nucleus and can act as transcription factors. 6. Answer: a. The operator contains a sequence that can attach to an inhibitory protein in order to stop the production of the trp gene sequence. 7. Answer: d. Histone acetylation will decrease the binding activity of histone proteins to the DNA molecule so that transcription of the DNA sequence can happen. 8. Answer: a. In genomic printing, certain DNA segments get methylated so that

DNA gets distinguished as being maternal or paternal in origin. Some genes, as a result, get expressed while others do not. 9. Answer: a. Most of the time, a mutation has no effect on the cell. Less commonly, some of the other effects can be seen, which are more dangerous complications for the cell. 10. Answer: c. A point mutation involves simply the substitution of one base for another. In sickle cell disease, glutamine is substituted for valine, leading to an abnormal hemoglobin protein.

ANSWERS TO CHAPTER NINE

1. Answer: b. The reactions that occur in the process of chemoorganotrophy is oxidation, which is the taking of an organic substance, progressively oxidizing it, and turning it into a more oxidized substance, such as into CO2 and water. 2. Answer: a. In this process, glucose and other organic chemicals have electrons to donate. They donate them to the final electron acceptor in aerobic respiration to create energy. In this case, the final electron acceptor is oxygen. 3. Answer: d. The major difference is that the Krebs cycle is not used in fermentation but it is used in anaerobic metabolism. 4. Answer: c. All glycolysis in the cell takes place in the cytoplasm. This is true for both prokaryotic cells and eukaryotic cells. 5. Answer: a. The first phase of glycolysis ends with two molecules of glyceraldehyde-3-phosphate, using up two ATP molecules in the process. 6. Answer: d. The molecule gets rearranged with any type of isomerase molecule. 7. Answer: d. Anaerobic metabolism cannot take place if cytochrome oxidase is unavailable to pass electrons to oxygen. 8. Answer: a. It is electrons that get transferred through the electron transport system so that hydrogen ions get pumped out of the cell, creating the proton motive force and a pH gradient. 9. Answer: b. The light-dependent reactions will make the high-energy products, which are ATP and NADPH, which are later used in the light-independent reactions. 10. Answer: a. There is ATP, NADPH, and CO2 that enter the cycle, which glyceraldehyde-3-phosphate used as its end product. This goes on outside of the cycle to make glucose.

ANSWERS TO CHAPTER TEN

1. Answer: a. Ribosomes are not one of the membrane-bound organelles that will participate in vesicular budding. This budding only happens when an organelle is membrane-bound. 2. Answer: d. Because vesicles are most likely to bud off of a membrane, they are actually surrounded by these membranes, making them glycerophospholipids, made in the endoplasmic reticulum. 3. Answer: a. Each of these is a typical vesicle coat protein except for dynamin, which is used to pinch off clathrin-coated vesicles. 4. Answer: d. These accidental proteins are sent back to the endoplasmic reticulum, where they belong. 5. Answer: d. There are endosomal compartments that will make the vesicles necessary for neurotransmitter release. The neurotransmitters are filled after the vesicles are made. 6. Answer: a. Calcium is increased in concentration in the presynaptic cell, causing the release of neurotransmitters into the synaptic cleft. 7. Answer: a. Synapsin I gets a phosphate group attached to it by ATP so it has a decreased affinity for actin. This allows the vesicle to move toward the active zone in the presynaptic area. 8. Answer: b. It is in the active zone where the neurotransmitters get released by the presynaptic nerve cell into the synaptic cleft. 9. Answer: b. The first place the vesicles go in the endocytic pathway is the early endosome, where they are uncoated and start the sorting process. 10. Answer: d. There are other proteins but clathrin is the main protein that forms a pit so the membrane is drawn into the vesicle in the process of endocytosis.

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ANSWERS TO CHAPTER ELEVEN

1. Answer: c. Neurotransmitters are associated with paracrine cell signaling, which involves connection between nearby cells that does not involve direct cell to cell contact. Neurotransmitters mediate this sort of thing. 2. Answer: d. Endocrine signaling happens over very large distances in the organism—often spanning the entire organism. 3. Answer: a. The main effect of the binding of an intracellular ligand is the induction of transcription of DNA. There is gene regulation so that certain genes get turned on. 4. Answer: d. Plasmodesmata involves cell to cell signaling between two different cells that are next to each other in plant organisms. 5. Answer: a. Threonine, serine, and tyrosine have a hydroxyl group, allowing for these to be phosphorylated. The glutamate amino acid does not have this hydroxyl group so it cannot be phosphorylated. 6. Answer: d. The MAP kinase signaling pathway is a growth factor pathway that involves the promotion of cell division. When overactive, the pathway can lead to cancerous changes in the cell. 7. Answer: b. Each of these is a typical second messenger except for ATP, which does not normally act specifically as a second messenger inside a cell. 8. Answer: a. When phosphodiesterase acts on cyclic AMP, it becomes AMP, which is completely inactive. In that way, the enzyme deactivates cyclic AMP. 9. Answer: c. This is also referred to as a seven-pass receptor because it passes through the membrane seven times as part of its structure. 10. Answer: a. When the ligand gets bound, there is a conformational change that allows GTP to replace GDP on the G protein.

ANSWERS TO CHAPTER TWELVE

1. Answer: b. The cytoskeleton is a highway for molecular transport and holds ribosomes in place in prokaryotic cells. They do not have organelles and it does not participate in cell to cell communication. 2. Answer: a. Actin is considered the thinnest filaments because it takes two of these wound together to make the very thin microfilaments. 3. Answer: b. The lamin protein is found exclusively in the nucleus, where it is responsible for holding up the nuclear envelope. 4. Answer: c. It is the microtubules that participate in the separation of sister chromatids in cells that are actively dividing. 5. Answer: a. The microfilaments of the cell do all of these things but they do not draw chromosomes apart in the process of cell division. 6. Answer: a. Two actin filament strands wind together in order to make microfilaments, which are the thinnest filaments—only six to seven nanometers in diameter. 7. Answer: b. I bands are light bands that are seen on electron microscope of muscle cells. They contain only actin filaments. 8. Answer: a. The Z bands are physically seen as the structures that are at the ends of the sarcomere. These can be seen as jagged lines across the myofibril on electron microscopy. 9. Answer: c. The hydrolysis of ATP must take place in order to drive the interaction between actin and myosin in the act of contracting the muscle. 10. Answer: d. Each of these is directly linked to the actin molecule but the titin molecule isn’t associated to actin but is instead associated with myosin.

ANSWERS TO CHAPTER THIRTEEN

1. Answer: a. During the S phase, DNA polymerase is active in the synthesis of new DNA. 2. Answer: d. Interphase involves the G1 phase, S phase, and G2 phase. The M phase is not a part of this process as it involves mitosis or the “mitotic phase”. 3. Answer: c. In the G2 phase, the cytoskeleton gets broken down and its components get ready for the process of mitosis. 4. Answer: d. G0 is a quiescent phase, in which the cell does not participate at all in the cell division process. The rest of the phases are participatory in the cell division process in some way. 5. Answer: b. In the late G1 phase, if there is too much of the protein made in the tumor repressor gene p53, the cell cycle does not continue and the process of cell apoptosis takes place. 6. Answer: a. Cells undergoing uncontrolled cell growth will participate in the M phase more commonly and to a greater degree. 7. Answer: d. Maturation-promoting factor will trigger a cell to enter the M phase of the cell cycle. 8. Answer: c. Its main job is to break down the nuclear envelope so that mitosis can proceed. 9. Answer: c. The sister chromatids get pulled apart in mitosis during the anaphase part of the process. They then are called daughter chromosomes. 10. Answer: b. During telophase, the nuclear envelope gets rebuilt in order to have the daughter chromosomes encapsulated again.

ANSWERS TO COURSE QUESTIONS

1. Answer: a. Cations are positively charged because they have lost an electron.

On the other hand, anions have gained an electron and are negatively charged. 2. Answer: c. Each of these is true of water except that it has a high surface tension and not a low surface tension. This means that it will take increased force to break a liquid water surface. 3. Answer: d. The lattice energy is another way to describe the bond strength of an ionic molecule. A high bond strength means that the energy it takes for the molecule to form a solid lattice is favorable. 4. Answer: d. Covalent compounds can be seen in either gases, liquids, or solids at normal room temperature and pressure. 5. Answer: c. Ionic compounds can be seen only in solid form at room temperature and pressure. They have high melting points so it would be rare to see them in liquid or gaseous form. Remember that, while ionic compounds easily dissolve in water under these conditions but, without water, they would be solidified. 6. Answer: d. Each of these statements is true of covalent molecules and covalent bonds; however, they have low boiling points as well as low melting points. 7. Answer: d. Sugars and carbohydrates are made only from carbon, oxygen, and hydrogen. There is no nitrogen in sugars. 8. Answer: c. Ribose is a five-carbon sugar used in the making of the RNA molecule. The rest are six-carbon sugars. 9. Answer: b. Each of these is a disaccharide except for galactose, which is a sixcarbon monosaccharide sugar. 10. Answer: b. Each of these is considered part of a nucleotide except for amino acids, which are part of a protein molecule and not a nucleic acid. 11. Answer: d. Hydrogen bonds between the nitrogenous bases make the DNA double stranded.

12. Answer: c. Adenosine triphosphate or ATP is a high-energy molecule that gives of a great deal of energy when the phosphate linkage is broken to make

ADP or adenosine diphosphate. 13. Answer: d. Enzymes can do each of these things but it does not change the starting or finishing energy levels of a given reaction. Instead, it changes the energy of activation. 14. Answer: c. Plasmids contain DNA within them. This DNA is considered extrachromosomal DNA because it is not part of the regular genome. 15. Answer: a. The cell wall determines the different ways that an organism stains with a gram staining technique. Gram-positive organisms stain positively because they have a thick peptidoglycan wall, which is not seen in gramnegative organisms. 16. Answer: c. Each of these is a way to transfer DNA from one cell to another.

True sexual reproduction does not happen in bacteria but they do undergo conjugation, in which one bacterium injects DNA into another via one of their pili. 17. Answer: b. The rough endoplasmic reticulum is the part of the eukaryotic cell that makes proteins. It is continuous with the nuclear envelope in order to allow RNA to pass from the nucleus to the part of the cell that participates in protein synthesis. 18. Answer: a. The peroxisomes contain oxidative molecules that get rid of toxins and waste products within the cell. 19. Answer: c. The process of osmosis applies only to water as it travels from an area of high concentration to an area of low concentration across a semipermeable membrane. 20.Answer: a. The nucleolus is the part of the nucleus that makes ribosomes as one of its major functions. The nucleolus resides within the nucleus of the cell. 21. Answer: b. The mitochondrion is an energy-making part of the cell, essential because it has multiple chemical reactions that participate in the making of

ATP energy, turning nutrients into carbon dioxide and water.

22.Answer: c. The main byproduct of the photosynthetic process, the purpose of which is to make glucose, is oxygen, which is not used by the plant cell but is given off after glucose is synthesized. 23.Answer: b. Each of these is contained within the chloroplast and the mitochondria; however, the thylakoids are just seen in the chloroplasts but not in the mitochondria. 24.Answer: d. Cellulose is what the cell wall of plants are made from. The other substances can be components of other cell walls. 25. Answer: a. Each of these is a signaling method that acts on a specific cell.

Only endocrine signaling can act, however, over a long distance within the organism. 26.Answer: c. Epithelial cells have a nerve supply so they are innervated; however, they do not have capillaries that reach up into the tissue so these cells are not vascular. 27. Answer: d. It is the apical side of the epithelium that has microvilli, which extend into the lumen of ducts and body cavities of different types. Not all epithelial cells have microvilli. 28.Answer: c. Gap junctions are connections between cells of the same tissue type to have small molecules pass between the cells. They connect these cells chemically as well as physically. 29.Answer: a. Adipose cells or fat cells are considered connective tissue cells that serve an energy reservoir function in the body. 30.Answer: a. These cells have each of these descriptions; however, they are irregularly arranged so they do not appear striated. 31. Answer: d. The microglia or microglial cells are responsible for clearing out pathogens and cellular debris in the nervous system. 32.Answer: d. Tight junctions allow for paracellular transport, which is the transport of certain molecules and ions between the cells that are semi-fused together with these types of junctions. 33. Answer: b. Each of these represents a protein that is part of making the tight junction, except for elastin, which is a connective tissue protein that is not part of the tight junction.

34.Answer: c. The hemidesmosome does not connect a cell to another cell.

Instead it connects the cell to connective tissue or to the basement membrane in the tissues. The others directly connect one cell to another. 35. Answer: d. While adherens junctions and desmosomes have the same cadherins proteins, they also have dissimilar proteins such as intermediate filaments, plakophilin, and desmoplakin. 36.Answer: b. Gap junctions are connecting adhesions between two cells that will allow an electrical signal to pass from one cell to its neighboring cell. 37. Answer: a. The gap junction involves two connexons that connect between two cells and allow for chemical and electrical activity to occur from cell to cell. 38.Answer: a. Laminin is the main protein in the basement membrane, forming a lattice network that attaches the cell to the underlying connective tissue. 39.Answer: d. The thymus is a gland so it is not connective tissue. Blood, bone, and fatty tissue are considered types of connective tissue. 40.Answer: c. The main cell seen in connective tissue is the fibroblast, which makes collagen. The other cells are seen less commonly in connective tissue of different types. 41. Answer: b. Type II collagen is the type of collagen seen in cartilage. You need to know that there are different types of collagen and that type I is in normal connective tissue and type II is in cartilage. 42.Answer: a. Cardiac muscle gets its elasticity from the myofibrils and not from the presence of elastin. The skin, lungs, bladder, and arteries all rely on elastin as a major component of the tissue; elastin is necessary to keep these tissues stretchy. 43.Answer: c. Fibrillin-1 gives the elastic fiber its fibrous nature. It combines with elastin to make the elastic fiber more fibrous. 44.Answer: a. Fatty acid synthesis takes molecules in the cytoplasm and makes fatty acids using multiple enzymes called fatty acid synthases. 45. Answer: b. Phospholipids are similar in structure to triglyceride molecules.

The main difference is that there are just two fatty acids on the phospholipid

molecule; there is a phosphate group in place of one of the fatty acids, which is attached to an alcohol group on the glycerol molecule. 46.Answer: b. Aquaporins are, for the most part, unable to pass any other molecule through it except for water, which is rapidly transported across the cell membrane via this mechanism. 47. Answer: c. Plant cells in pure water draw the water into the cells via osmosis, making them turgid. Only in saltwater will the plant cells become flaccid or plasmolyzed. Transpiration is evaporation from the leaves of the plant. 48.Answer: d. While each of these will dissolve in water, sodium chloride has two solutes—sodium and chloride—so that its osmotic pressure will be greater. 49.Answer: c. Filtration happens in the glomerulus of the kidneys, because of the hydrostatic pressure of the cardiovascular system that forces solutes and water through small pores in the glomeruli. 50.Answer: d. The concentration gradient for primary active transport can be downward or upward. It can just as easily go in an upward concentration gradient—from a low to a high concentration across the membrane. 51. Answer: a. The sarcoplasmic reticulum acts to pump and release calcium ions in the muscle cell in order to participate in muscle contraction. There are special P-class pumps that pump calcium into the sarcoplasmic reticulum after they are used for muscle contraction. 52. Answer: d. F-class pumps are located on mitochondria, chloroplasts, and bacterial cell membranes. They make ATP so these are also referred to as ATP synthases. 53. Answer: b. The ABC-class pump is actually a superfamily of pumps that will pump both small ions and molecules across the cell membrane. This is the only classification of pumps that pumps small molecules across the membrane. 54. Answer: a. It is the primary active transport of sodium ions, creating an electrochemical gradient, that causes the secondary transport of other molecules. This is referred to as either a symport or antiport mechanism. 55. Answer: b. Each pass of the sodium-potassium ATPase pump requires just one ATP molecule to be used up.

56. Answer: d. With each pass of the sodium-potassium ATPase pump, three molecules of sodium leave the cell and two molecules of potassium enter the cell. 57. Answer: a. While the sodium-potassium ATPase pump does each of these things, it does not affect the pH of the inside or outside of the cell. 58.Answer: d. The polarized cell under normal, resting conditions has a resting membrane potential of – 70 millivolts. 59. Answer: d. All cells have a sodium-potassium ATPase pump. The voltagegated channels that lead to depolarization and repolarization happen only in certain cells. 60.Answer: b. The secondary structure of a protein molecule comes from hydrogen bonding between amino acids, leading to an alpha helix or a beta pleated sheet. 61. Answer: d. The quaternary structure is what is created by a protein when more than one peptide interacts with others within the protein. 62.Answer: c. The tertiary structure of a protein is the three-dimensional shape that is made by several different types of bonds between the R groups of the amino acids. 63.Answer: b. There needs to be three bases or a triplet of bases in order to have enough to encode for specific amino acids (of which there are twenty) plus triplets that stand for starting and stopping the reading process. 64.Answer: d. RNA polymerase is an enzyme that acts on DNA in the making of single-stranded messenger RNA molecules that go on to make proteins. 65. Answer: a. The promotor region is involved in the initiation process of RNA transcription, where the process of reading the gene first begins. 66.Answer: d. The process of translation takes place within the ribosomes of the cell. Transcription, on the other hand, is what happens in the nucleus of the cell. 67. Answer: c. While there are just 20,000 different genes in the genome, there are more than a million unique proteins in the human proteome. 68.Answer: a. Most of these processes listed are reversible except for peptide cleavage or proteolysis, which tends to be an irreversible process.

69.Answer: d. In an enzyme system, each of these things happens; however, the enzyme is not consumed and will return to its natural state so that another reaction can occur. 70.Answer: a. Enzymes are all catalysts but not all catalysts are enzymes. Both help a reaction happen faster but enzymes are seen in biological processes.

Catalysts can be chemical substances. 71. Answer: d. The protein does not need to be separated from other proteins in order to do the test. The protein is selected from the other proteins in the sample because it is selectively bound to the antibody that is affixed to a plate. 72. Answer: a. There is hydrogen bonding in the DNA molecule that causes cytosine to bond with guanine. 73. Answer: b. Uracil takes the place of thymine in the RNA molecule so that there is no thymine in RNA but only uracil. There is no uracil in the DNA molecule. 74. Answer: c. The main purpose of histone proteins is to condense DNA into chromatin. Without histones, DNA would be one long strand that would stretch too long to fit in the nucleus. 75. Answer: b. DNA is found in each of these structures; however, it is not found in the ribosomes of the cell. Because chloroplasts and mitochondria were probably evolutionarily derived from bacterial organisms, they do contain

DNA. 76. Answer: c. In general, the structure of DNA makes DNA more structurally stable than RNA. RNA is generally single-stranded, contains ribose instead of deoxyribose, and has shorter strands than DNA. 77. Answer: d. A string of uracils together cause weak linkage in the connection between the DNA and RNA molecule, which causes the RNA molecule to slip off the DNA, freeing itself from RNA polymerase. 78. Answer: d. The template strand is the strand that is the original DNA strand that gets made into the transcript. The coding strand is the opposite DNA strand to the template strand; it is also made of DNA. 79. Answer: b. The DNA template strand gets read from the three-prime end to the five-prime end, adding RNA bases one at a time.

80.Answer: a. Adenine is added in sequence to make the poly-A tail on messenger RNA. It protects the messenger RNA so that it can leave the nucleus for transcription. 81. Answer: a. Ribosomal RNA is more than just a structural RNA. It has enzymatic properties that catalyzes the connection between the amino acid and the messenger RNA. 82.Answer: b. Only viruses can have their genome be based on RNA, which can be double-stranded or single-stranded RNA. 83.Answer: d. DNA polymerase participates in elongation of the DNA strand during the process of DNA replication. 84.Answer: d. Telomerase forms telomers, which are the protective caps added to the ends of the DNA molecule in order to protect the ends and keep them from binding to one another. 85.Answer: c. Topoisomerase and DNA gyrase are the same enzymes necessary for unwinding and rewinding DNA in the replication process. 86.Answer: b. The main effect of UV light on the structure of DNA is the formation of pyrimidine dimers, where two dimers connect covalently to one another on the DNA molecule. 87. Answer: d. Factor for inversion stimulation most participates in the regulation of bacterial DNA sequences. Remember that bacterial DNA does not contain histone proteins; topoisomerase I and DNA gyrase both help to supercoil the bacterial genome. 88.Answer: b. The DNA projects out of the nucleoid, where it transcribes and translates at the same time associated with ribosomes located in the cytoplasm. 89.Answer: d. Lactose is the main inhibitory molecule. It binds to the regulator regions when lactose is present. This prevents the transcription of molecules that would normally cause lactose uptake and metabolism, which would be used for food. If lactose is present, these enzymes are not necessary. 90.Answer: c. Cis-acting genes are genes that are located adjacent to one another.

There is usually one promotor site for the genes that are cis-acting genes.

91. Answer: a. An enhancer sequence helps a gene or gene sequence get transcribed to a higher degree of efficiency. 92.Answer: c. The transcription activator has two parts. It binds to specific DNA sequences and activates gene transcription by also interacting with transcription machinery. 93.Answer: c. In this case, tryptophan is a corepressor that binds to the trp repressor gene so that the transcription of the trp operon can be blocked. 94.Answer: d. In the attenuation process, transcription can happen but a short, non-functional mRNA molecule is made and the transcription process does not complete itself. 95. Answer: b. Eukaryotic repressor proteins will bind to regulator sites, acting in direct opposition to eukaryotic activator proteins. 96.Answer: b. Transposable DNA is found in prokaryotes and eukaryotes in large numbers, making up about half of all human DNA. 97. Answer: c. Reverse transcription is when RNA gets transcribed into DNA. It happens in virus particles as well as in other cells that have class 1 transposable DNA. 98.Answer: d. The majority of the time, the effect of a transposon is silent and it causes no specific human disease whatsoever. 99.Answer: b. The mutation is a point mutation that is nonconservative, meaning that the protein does not behave the same way as the original protein. This makes it a nonconservative missense point mutation. 100. Answer: a. The deletion of a single base pair is the most dangerous because it results in a frameshift mutation so that the rest of the DNA message is completely garbled and makes no sense. 101. Answer: d. Very rarely, DNA polymerase can put in the wrong base pair, resulting in a mutation. This is rare because there are proofreading enzymes that will fix the error before the next replication. 102. Answer: d. There are direct pathways that turn amino acids, fatty acids, and sugars into energy and oxidized substances. In general, this does not occur with nucleic acids unless they are broken down into sugars or other substances.

103. Answer: b. Because energy is required to start the process of glycolysis, only two ATP molecules are generated per glucose molecule in the process. 104. Answer: c. Each of these names is synonymous with the other; however, the Cori cycle is something completely different and involves the conversion of lactic acid into glucose by the liver after anaerobic metabolism. 105. Answer: c. About 32 molecules of ATP are made per molecule of glucose when all parts of aerobic respiration are taken into account. 106. Answer: a. Each of these can be a final common electron acceptor in anaerobic respiration. Because the process is anaerobic, however, the process does not include oxygen. 107. Answer: a. All kinase enzymes cause the phosphorylation of a molecule. 108. Answer: d. Hexokinase is an enzyme that turns the glucose or hexose molecule into glucose-6-phosphate. 109. Answer: b. Because this is a kinase, it takes fructose-6-phosphate, and turns it into fructose-1,6 bisphosphate, which has two phosphate molecules attached to it. 110. Answer: c. ATP provides the phosphate to the molecules in the glycolysis pathway, turning it into ADP, which is an energy-requiring step. 111. Answer: c. Both ATP and NADH are produced by the second half of the glycolysis pathway. These make up for the lost ATP molecules in the first half of glycolysis, yielding two extra ATP molecules plus 2 NADH molecules—both of which are high energy. 112. Answer: a. The end-product of glycolysis is pyruvate. Two molecules of pyruvate are made for every molecule of glucose that begins the process. 113. Answer: c. Denitrifying bacteria will use nitrate and nitrite as final electron acceptors to yield the end product, which is nitrogen gas. 114. Answer: b. The protons get pumped into the intramembranous space in the mitochondria, creating an electrochemical gradient as well as a pH gradient. 115. Answer: d. The enzyme ATP synthase is directly tied to the leakage of hydrogen ions across the mitochondrial or cytoplasmic membrane.

116. Answer: c. The source of energy for oxidative phosphorylation is the proton motive force, which is generated across a membrane. 117. Answer: c. ATP synthase is the only one of these proteins that does not participate within the electron transport system. 118. Answer: d. Three NADH molecules are made with each turn of the Krebs cycle, along with one molecule of FADH2 and one molecule of ATP. 119. Answer: a. It is pyruvate that gets transported from the cytoplasm to the mitochondrion in order to eventually get transformed into what participates in the Krebs cycle. 120. Answer: b. Acetyl CoA is released in the oxidation of fatty acids. This process is also referred to as beta-oxidation. 121. Answer: a. Normally, beta oxidation occurs but, in branched-chain fatty acids, alpha oxidation may occur as a minor metabolic pathway. 122. Answer: c. Glucose is not necessary for photosynthesis; however, it is an end-product of photosynthesis and not a starting substrate. 123. Answer: d. One particle of light is referred to as a photon. This is what gets absorbed in order to have photosynthesis take place. 124. Answer: d. It takes six turns of the cycle, in which one CO2 molecule is built into a six-carbon sugar, such as glucose. Three actual turns make glyceraldehyde-3-phosphate, which is the cycle’s endpoint. 125. Answer: c. In photosynthesis, water and carbon dioxide are reactants and glyceraldehyde-3-phosphate and oxygen are end-products of the reactions. 126. Answer: b. Cyanobacteria use each of these things as part of photosynthesis but they do not make use of chloroplasts because these are prokaryotic cells that do not have chloroplasts. 127. Answer: a. The light-independent reactions take place in the stroma of the chloroplasts in eukaryotic cells. 128. Answer: c. Thylakoids are stacked membranes but they are not a maze of membranes. They contain chlorophyll and the outside of them is called the stroma.

129. Answer: a. The photosystem has antenna molecules attached to chlorophyll pigments in what’s called a reaction center. It does not include

ATP synthase, which is a separate component that relies on a proton gradient. 130. Answer: b. Similar to what’s seen in mitochondria, it is the proton gradient that drives the ATP synthase in the chloroplast. 131. Answer: b. The transport of vesicles in the eukaryotic cell is from the endoplasmic reticulum to the cis Golgi to the medial Golgi, and to the trans

Golgi. The reverse can happen rarely if the original transport was in error.

This would mean that the errant proteins are returned back to the endoplasmic reticulum. 132. Answer: c. The clathrin coating protein on vesicles allow the vesicle to get from the Golgi apparatus to the plasma membrane. 133. Answer: b. Clathrin requires dynamin and GTP energy in order to pinch off a vesicle. COPI and COPII do not require anything in order to do this process. 134. Answer: b. It takes a low pH and high calcium concentration milieu in order to aggregate proteins in the vesicles so that there can be high concentrations of these proteins inside the vesicle. When discharged, though, the opposite situation occurs so that there is release of the proteins into whatever space they are discharged into. 135. Answer: a. It is a t-SNARE protein on the target membrane that docks with the v-SNARE protein on the vesicle. When these proteins match, there is attachment and ultimately the release of the vesicle outside of the target membrane. 136. Answer: c. The SNARE proteins will twist with one another so that the vesicle can be attached and so that it can be discharged into the target membrane lumen. 137. Answer: c. Each of these is a SNARE-type protein, which participates in the connection of synaptic vesicles to the presynaptic cell membrane. The exception is dynamin, which does not participate in this process.

138. Answer: b. VAMPs are vesicle-associated membrane proteins that hold vesicles in place before they need to be discharged in the nerve cells. They attach the vesicles to the cytoskeleton. 139. Answer: c. After the empty vesicle is made or recycled, it is filled with neurotransmitter for eventual release at the time of the action potential. 140. Answer: d. Actin is the part of the cytoskeleton that attaches vesicles in nerve cells before they are ready for release into the synaptic cleft. 141. Answer: c. Synaptophysin has properties that help the presynaptic membrane open up a pore when the vesicle is ready to be released. 142. Answer: d. Physophilin and synaptophysin bind together to make the pore necessary for the vesicle to empty itself of neurotransmitters through the presynaptic cell membrane. 143. Answer: a. Clathrin-dependent endocytosis is also referred to as receptormediated endocytosis. The others listed are other types of endocytosis. 144. Answer: c. The act of potocytosis involves the uptake of molecules into buds and vesicles that just get released into the cytosol of the cell rather than to a lysosome or other organelle. 145. Answer: a. The LDL-receptor gets recycled. It gets taken up by a vesicle and is sent back to the exterior of the cell. 146. Answer: c. Things get increasingly acidic from the exterior of the cell to the coated vesicle to the early endosome to the late endosome and finally, to the lysosome, which is the most acidic, having a pH of 4.8. 147. Answer: d. Mucolipidosis II disease is the most serious lysosomal storage disease because nearly none of the lysosomal enzymes are present due to a genetic defect involving the function of all of these enzymes. 148. Answer: b. The iron leaves after being bound to an intracellular protein.

The transferrin-receptor complex gets recycled back to the cell surface, where they then dissociate from one another. 149. Answer: a. Autocrine cell signaling involves a cell making a ligand or signal for its own receptors. It can have a separate paracrine function as well. 150. Answer: b. In animal cells, gap junctions connect two cells together to allow for direct cell to cell communication.

151. Answer: c. Intracellular ligands are usually hydrophobic molecules that can pass the plasma membrane by themselves. Examples include the sex hormones like estrogen and testosterone. 152. Answer: b. When the receptor gets activated, tyrosine on the inside of the cell is able to be phosphorylated. 153. Answer: c. Norepinephrine is not hydrophobic nor can it pass through the cell membrane. It therefore needs to bind on the outside of the cell. The rest will bind inside the cell as intracellular ligands. 154. Answer: b. The ligand located by itself is the most upstream of the events that occur with the ligand itself binding to the receptor, activating an intracellular signaling molecule, and ultimately doing something like activating a gene. 155. Answer: b. Calcium is a frequent second messenger in the cell. Its concentration is increased through ligand-gated calcium channels that increase its concentration in the cell, where it affects the ability of a protein to do its job. 156. Answer: c. Adenylyl cyclase is an enzyme that catalyzes the conversion of

ATP to cyclic AMP because cyclic AMP is necessary as a second messenger. 157. Answer: d. Calcium is the second messenger in the contraction of muscle cells. Calcium concentration is increased so that the activity of the cell is to contract. 158. Answer: b. Each of these stays as part of the plasma membrane; however,

IP3 is able to enter the cytoplasm in order to continue a signaling cascade. 159. Answer: d. The making of a protein can be changed through the turning off of a gene, the turning on of gene transcription, or the turning on of protein translation. 160. Answer: b. There is a change in enzyme activity so that the activity of glycogen synthase is turned off and the activity of glycogen phosphorylase gets turned on, making more glucose molecules. 161. Answer: d. G protein-coupled receptors are not found in prokaryotic cells but it is found in eukaryotic cells only.

162. Answer: c. The microfilaments are the filaments that participate in the process of cytokinesis in the cell. This is when a cell becomes two daughter cells after the division of nuclear material. 163. Answer: d. Microfilaments aid in cytoplasmic streaming, which is the movement of cell structures and molecules within the cell. 164. Answer: a. It is the microfilaments that aid in amoeba movements, allowing them to move in response to certain chemical or physical situations. 165. Answer: d. It is the intermediate filaments that give the cell its basic shape by creating a specific cell structure. These are sturdier than other filaments in the cytoskeleton. 166. Answer: a. The microtubules get together and react to make the flagella of the cell move. 167. Answer: d. A centrosome is also called a microtubule organizing center because microtubules exit this structure. 168. Answer: b. When microfilaments contract, they draw in vesicles that contain substance in the act of endocytosis. 169. Answer: c. Microtubules are tubular and are made from alpha and beta tubulin. These are the thickest of the different filaments in the cell. 170. Answer: c. Myosin interacts with actin in order to cause muscles to contract. Tubulin proteins are used in microtubules and autoclampin participates in actin creation when it assembles. 171. Answer: b. Actin forms a cinch that pinches off a cell after the nuclear material has separated so that there can be physical separation of a dividing cell into two cells. 172. Answer: a. A single contractile cell in muscle tissue is called a muscle fiber. 173. Answer: c. A sarcomere is what’s referred to when talking about a single contractile unit. 174. Answer: c. The titin molecule is large and acts like a spring that keeps the myosin fragments organized as the muscle contraction occurs. 175. Answer: d. The A band is the actin-myosin complex. It increases in length during muscle contraction, allowing the H zone, which is myosin only, and the

I band, which is actin only, to come together.

176. Answer: b. The M line is the middle of the sarcomere. It is here when the myosin segments reverse in their polarity so the sarcomere is symmetric from one side to another. 177. Answer: a. Calcium is released by the sarcoplasmic reticulum. The concentration of calcium determines whether or not the muscle contracts. 178. Answer: b. Troponin C is the polypeptide that binds to calcium in order for there to be an interaction between troponin and tropomyosin. 179. Answer: c. There is a part of the myosin molecule that gets phosphorylated in order to allow for muscle contraction. There is a kinase that performs this process. 180. Answer: a. Calcium binds to calmodulin in non-muscle cells in order for the contraction of the cell to occur. 181. Answer: a. The tubulin is a part of the microtubules that gets built at the leading edge of the migrating cell. It forms microtubules that adhere to the matrix and help the cell migrate from one place to another. 182. Answer: c. Animal cells only have centrosomes. The microtubule organizing center in plants and fungi is the nuclear envelope and not the centrosomes. 183. Answer: d. The kinetochore microtubules will actually connect to the chromosomes in order to pull them apart during the process of mitosis. 184. Answer: b. Intermediate filaments will attach to the desmosomes and hemidesmosomes outside of the cell in order to provide structure to the cell in relation to other cells near it. 185. Answer: d. There are eighteen tubules around the structure and a central doublet for a total of twenty microtubules in a structure that makes up a flagellum or cilium. 186. Answer: c. Each of these is participatory in the process of making a flagellum or cilium move. Nebulin, however, is not involved. 187. Answer: b. The mitotic spindle is made out of a pair of centrosomes that together form the mitotic spindle during the S phase of interphase. 188. Answer: b. It is during the S phase that centrioles and centrosomes get made and duplicated.

189. Answer: a. The G1 phase is biochemically active with a great many nucleic acids and proteins getting made in the process, even though the cell itself does not change much in appearance. 190. Answer: a. A neuron is almost always going to be in the G0 phase because, once it is made, it is quiescent and doesn’t undergo cell division. 191. Answer: d. In the M phase, the karyotype is most visible. It is generally not visible under light microscopy in the other phases. 192. Answer: c. The newly dividing cell starts out the cell cycle in the G1 phase, where it prepares to divide again. Only nondividing cells go through a G0 phase. 193. Answer: d. Only after getting through the G2 phase is the cell completely committed to cell division. It needs to get through the G2 checkpoints. 194. Answer: b. There is a well-known metaphase checkpoint that makes sure the microtubules are attached and that the karyotype is aligned before the cell cycle can continue. 195. Answer: a. Proteins that start the S phase get activated when the G1/S cyclin binds to the cyclin-dependent kinase. 196. Answer: a. It causes the sister chromatids to separate by causing the breakdown of the cohesin protein, which will normally hold the sister chromatids together. 197. Answer: d. If p53 is deficient, missing, or damaged, there can be cancerous changes in the cell because mutations get passed on to the next generation. 198. Answer: a. Prophase takes up over half of the entire mitosis cycle, which itself is about an hour long. 199. Answer: a. It is during prophase I that recombination or crossing over occurs, leading to unique chromosomes that separate after meiosis I occurs. 200. Answer: c. In both mitosis and meiosis I, there is a metaphase plate that develops, with the chromosomes lined up on either side of the plate.