section 3 cell bio
17-31 The graph in Figure Q17-31 shows the time course of the polymerization of pure tubulin in vitro. Assume that the starting concentration of free tubulin is higher than it is in cells.Figure Q17-31Three parts of the curve are labeled above it as A, B, and C. You conduct a similar in vitro tubulin-polymerization experiment, only you include purified centrosomes in your preparation. When you plot your data, which part of your graph should be most dissimilar to the curve shown in Figure Q17-31? (a) A (b) B( c) C (d) None. The shape of my graph should be identical to the graph produced when tubulin is polymerized in the absence of purified centrosomes.
(a) A
20-54 Which of the following genetic changes cannot convert a proto-oncogene into an oncogene? (a) A mutation that introduces a stop codon immediately after the codon for the initiator methionine. (b) A mutation within the coding sequence that makes the protein hyperactive. (c) An amplification of the number of copies of the proto-oncogene, causing overproduction of the normal protein. (d) A mutation in the promoter of the proto-oncogene, causing the normal protein to be transcribed and translated at an abnormally high level.
(a) A mutation that introduces a stop codon immediately after the codon for the initiator methionine.
17-46 Compared to the normal situation, in which actin monomers carry ATP, what do you predict would happen if actin monomers that bind a nonhydrolyzable form of ATP were incorporated into actin filaments? (a) Actin filaments would grow longer. (b) Actin filaments would grow shorter because depolymerization would be enhanced. (c) Actin filaments would grow shorter because new monomers could not be added to the filaments. (d) No change, as addition of monomers binding nonhydrolyzable ATP would not affect actin filament length.
(a) Actin filaments would grow longer.
20-11 Which of the following statements about collagen is false? (a) Collagen synthase organizes the mature collagen molecules into ordered collagen fibrils. (b) Collagen is synthesized as procollagen and secreted to the outside of the cell in a secretory vesicle. (c) The terminal procollagen domains are cleaved by a protease in the extracellular space. (d) Cells can break down a collagen matrix using matrix proteases.
(a) Collagen synthase organizes the mature collagen molecules into ordered collagen fibrils.
20-15 Which of the following statements about integrins is false? (a) Integrins use adaptor proteins to interact with the microtubule cytoskeleton. (b) Integrins can switch to an activated state by binding to an extracellular matrix molecule. (c) Integrins can switch to an activated state by binding to an intracellular protein. (d) An activated integrin molecule takes on an extended conformation.
(a) Integrins use adaptor proteins to interact with the microtubule cytoskeleton.
17-20 Which of the following statements about the function of the centrosome is false?(a) Microtubules emanating from the centrosome have alternating polarity such that some have their plus end attached to the centrosome while others have their minus end attached to the centrosome.(b) Centrosomes contain hundreds of copies of the γ-tubulin ring complex important for microtubule nucleation.(c) Centrosomes typically contain a pair of centrioles, which is made up of a cylindrical array of short microtubules.(d) Centrosomes are the major microtubule-organizing center in animal cells. (
(a) Microtubules emanating from the centrosome have alternating polarity such that some have their plus end attached to the centrosome while others have their minus end attached to the centrosome.
17-21 Which of the following statements about microtubules is true?(a) Motor proteins move in a directional fashion along microtubules by using the inherent structural polarity of a protofilament.(b) The centromere nucleates the microtubules of the mitotic spindle.(c) Because microtubules are subject to dynamic instability, they are used only for transient structures in a cell.(d) ATP hydrolysis by a tubulin heterodimer is important for controlling the growth of a microtubule.
(a) Motor proteins move in a directional fashion along microtubules by using the inherent structural polarity of a protofilament.
20-3 Which of the following statements about plant cell walls is true? (a) The microtubule cytoskeleton directs the orientation in which cellulose is deposited in the cell wall. (b) The molecular components of the cell wall are the same in all plant tissues. (c) Because plant cell walls are rigid, they are not deposited until the cell has stopped growing. (d) The cellulose found in cell walls is produced as a precursor molecule in the cell and delivered to the extracellular space by exocytosis.
(a) The microtubule cytoskeleton directs the orientation in which cellulose is deposited in the cell wall.
20-51 A metastasis is _________.( a) a secondary tumor in a different part of the body that arises from a cell from the primary tumor. (b) a cell that is dividing in defiance of normal constraints. (c) a part of the primary tumor that has invaded the surrounding tissue. (d) the portion of the cancerous tumor that displays genetic instability.
(a) a secondary tumor in a different part of the body that arises from a cell from the primary tumor.
17-29 Which of the situations below will enhance microtubule shrinkage? (a) addition of a drug that inhibits GTP exchange on free tubulin dimers (b) addition of a drug that inhibits hydrolysis of the GTP carried by tubulin dimers (c) addition of a drug that increases the affinity of tubulin molecules carrying GDP for other tubulin molecules (d) addition of a drug that blocks the ability of a tubulin dimer to bind to γ-tubulin
(a) addition of a drug that inhibits GTP exchange on free tubulin dimers
20-31 Which type of junction involves a connection to the actin cytoskeleton?(a) adherens junctions (b) desmosomes (c) tight junctions (d) gap junctions
(a) adherens junctions
20-46 Induced pluripotent stem (iPS) cells ______________________. (a) are created by the expression of a set of key genes in cells derived from adult tissues so that these cells can differentiate into a variety of cell types. (b) require a supply of donor egg cells, such as embryonic stem cells. (c) can differentiate into a greater variety of adult tissues than embryonic stem cells. (d) are created by nuclear transplantation.
(a) are created by the expression of a set of key genes in cells derived from adult tissues so that these cells can differentiate into a variety of cell types.
20-22 Adherens junctions ______________________. (a) can be used to bend epithelial sheets into tubes. (b) are most often found at the basal surface of cells. (c) are found only in adult tissues. (d) involve fibronectin and integrin interactions.
(a) can be used to bend epithelial sheets into tubes.
6-13 DNA polymerase catalyzes the joining of a nucleotide to a growing DNA strand. What prevents this enzyme from catalyzing the reverse reaction? (a) hydrolysis of pyrophosphate (PPi) to inorganic phosphate (Pi) + Pi (b) release of PPi from the nucleotide (c) hybridization of the new strand to the template (d) loss of ATP as an energy source
(a) hydrolysis of pyrophosphate (PPi) to inorganic phosphate (Pi) + Pi
Use the following information about a series of in vitro DNA replication experiments to answer questions 6-16 through 6-22.You prepare bacterial cell extracts by lysing the cells and removing insoluble debris via centrifugation. These extracts provide the proteins required for DNA replication. Your DNA template is a small, double-stranded circular piece of DNA (a plasmid) with a single origin of replication and a single replication termination site. The termination site is on the opposite side of the plasmid from the origin.6-18 What part of the DNA replication process would be most directly affected if a strain of bacteria lacking primase were used to make the cell extracts? (a) initiation of DNA synthesis (b) Okazaki fragment synthesis (c) leading-strand elongation (d) lagging-strand completion
(a) initiation of DNA synthesis
20-34 Plasmodesmata ______________________.(a) permit small molecules to pass from one cell to another. (b) are found only in animal cells. (c) are closed by the neurotransmitter dopamine. (d) provide tensile strength.
(a) permit small molecules to pass from one cell to another.
20-40 When a terminally differentiated cell in an adult body dies, it can typically be replaced in the body by a stock of ________. (a) proliferating precursor cells. (b) cells more apically located than the terminally differentiated cells. (c) Wnt proteins. (d) induced pluripotent cells.
(a) proliferating precursor cells.
17-39 Which of the following items is not important for flagellar movement?(a) sarcoplasmic reticulum (b) ATP (c) dynein (d) microtubules
(a) sarcoplasmic reticulum
17-8 All intermediate filaments are of similar diameter because ____________.(a) the central rod domains are similar in size and amino acid sequence.(b) the globular domains are similar in size and amino acid sequence.(c) covalent bonds among tetramers allow them to pack together in a similar fashion.(d) there is only a single type of intermediate filament in every organism.
(a) the central rod domains are similar in size and amino acid sequence.
6-8 How many replication forks are formed when an origin of replication is opened? (a) 1 (b) 2 (c) 3 (d) 4
(b) 2
17-49 Which of the following statements is false? (a) Cytochalasins prevent actin polymerization. (b) Actin filaments are usually excluded from the cell cortex. (c) Integrins are transmembrane proteins that can bind to the extracellular matrix. (d) ARPs can promote the formation of branched actin filaments.
(b) Actin filaments are usually excluded from the cell cortex.
20-55 Which of the following statements about tumor suppressor genes is false? (a) Gene amplification of a tumor suppressor gene is less dangerous than gene amplification of a proto-oncogene. (b) Cells with one functional copy of a tumor suppressor gene will usually proliferate faster than normal cells. (c) Inactivation of tumor suppressor genes leads to enhanced cell survival and proliferation. (d) Individuals with only one functional copy of a tumor suppressor gene are more prone to cancer than individuals with two functional copies of a tumor suppressor gene.
(b) Cells with one functional copy of a tumor suppressor gene will usually proliferate faster than normal cells.tumor suppressor gene is recessive, so cell behaves normally
17-44 Consider the mechanism by which actin and tubulin polymerize. Which of the items below does not describe something similar about the polymerization mechanisms of actin and microtubules? (a) Although both filaments can grow from both ends, the growth rate is faster at the plus ends. (b) Depolymerization initiates at the plus ends of filaments. (c) Nucleotide hydrolysis promotes depolymerization of filaments. (d) Free subunits (actin and tubulin) carry nucleoside triphosphates.
(b) Depolymerization initiates at the plus ends of filaments.
7-10 Intermediate filaments are made from elongated fibrous proteins that are assembled into a ropelike structure. Figure Q17-10 shows the structure of an intermediate filament subunit. You are interested in how intermediate filaments are formed, and you create an intermediate filament subunit whose α-helical region is twice as long as that of a normal intermediate filament by duplicating the normal α-helical region while keeping a globular head at the N-terminus and a globular tail at the C-terminus; you call this subunit IFαd. If you were to assemble intermediate filaments using IFαd as the subunit, which of the following predictions describes the most likely outcome?Figure Q17-10(a) Filaments assembled using IFαd will interact with different cytoskeletal components.(b) Filaments assembled using IFαd will form dimers that are twice as long as dimers assembled from normal intermediate filaments.(c) Sixteen tetramers assembled from IFαd will be needed for a ropelike structure to form.(d) Dimers of IFαd will form by interactions with the N-terminal globular head and the C-terminal globular tail.
(b) Filaments assembled using IFαd will form dimers that are twice as long as dimers assembled from normal intermediate filaments.
20-65 APC is a tumor suppressor and acts in the Wnt signaling pathway to prevent the TCF complex from turning on Wnt-responsive genes. Mice that lack the gene encoding TCF4 do not have the ability to maintain the pool of proliferating gut stem cells needed to renew the gut lining. What do you predict will happen in mice that lack the APC gene? (a) Mice lacking the APC gene will be like the mice lacking TCF4 and not be able to renew the gut lining. (b) Mice lacking the APC gene will have inappropriate proliferation of gut stem cells. (c) Mice lacking the APC gene will have a hyperactive Wnt receptor even though there is no Wnt signal. (d) Mice lacking the APC gene will be like normal healthy mice, since APC is a tumor suppressor and thus not needed unless there is a tumor present.
(b) Mice lacking the APC gene will have inappropriate proliferation of gut stem cells.
17-26 You discover a protein, MtA, and find that it binds to the plus ends of microtubules in cells. The hypothesis that best explains this localization is ________________.(a) MtA is involved in stabilizing microtubules.(b) MtA binds to GTP-bound tubulin on microtubules.(c) MtA is important for the interaction of microtubules with the centrosome.(d) MtA will not bind to purified microtubules in a test tube.
(b) MtA binds to GTP-bound tubulin on microtubules.
17-32 Which of the following statements about organellar movement in the cell is false? (a) Organelles undergo saltatory movement in the cell. (b) Only the microtubule cytoskeleton is involved in organellar movement. (c) Motor proteins involved in organellar movement use ATP hydrolysis for energy. (d) Organelles are attached to the tail domain of motor proteins.
(b) Only the microtubule cytoskeleton is involved in organellar movement.
17-57 Figure Q17-57shows an electron micrograph of a skeletal muscle fiber, where various points along a fiber and various regions have been labeled.Figure Q17-57Which of the following statements is true about muscle contraction? (a) Point A will move closer to point B.(b) Point B will move closer to point C.(c) Region D will become smaller. (d) Region E will shrink in size.
(b) Point B will move closer to point C.
17-59 Which of the following statements about skeletal muscle contraction is false? (a) When a muscle cell receives a signal from the nervous system, voltage-gated channels open in the T-tubule membrane. (b) The changes in voltage across the plasma membrane that occur when a muscle cell receives a signal from the nervous system cause an influx of Ca2+ into the sarcoplasmic reticulum, triggering a muscle contraction. (c) A change in the conformation of troponin leads to changes in tropomyosin such that it no longer blocks the binding of myosin heads to the actin filament. (d) During muscle contraction, the Z discs move closer together as the myosin heads walk toward the plus ends of the actin filaments.
(b) The changes in voltage across the plasma membrane that occur when a muscle cell receives a signal from the nervous system cause an influx of Ca2+ into the sarcoplasmic reticulum, triggering a muscle contraction.
Use the following information about a series of in vitro DNA replication experiments to answer questions 6-16 through 6-22.You prepare bacterial cell extracts by lysing the cells and removing insoluble debris via centrifugation. These extracts provide the proteins required for DNA replication. Your DNA template is a small, double-stranded circular piece of DNA (a plasmid) with a single origin of replication and a single replication termination site. The termination site is on the opposite side of the plasmid from the origin.6-17 Which of the following statements is true with respect to this in vitro replication system? (a) There will be only one leading strand and one lagging strand produced using this template. (b) The leading and lagging strands compose one half of each newly synthesized DNA strand. (c) The DNA replication machinery can assemble at multiple places on this plasmid. (d) One daughter DNA molecule will be slightly shorter than the other.
(b) The leading and lagging strands compose one half of each newly synthesized DNA strand.
16-7 Which of the following statements is true? (a) Because endocrine signals are broadcast throughout the body, all cells will respond to the hormonal signal. (b) The regulation of inflammatory responses at the site of an infection is an example of paracrine signaling. (c) Paracrine signaling involves the secretion of signals into the bloodstream for distribution throughout the organism. (d) The axons of neurons typically signal target cells using membrane-bound signaling molecules that act on receptors in the target cells.
(b) The regulation of inflammatory responses at the site of an infection is an example of paracrine signaling.
17-58 Which of the following conditions is likely to decrease the likelihood of skeletal muscle contraction? (a) partial depolarization of the T-tubule membrane, such that the resting potential is closer to zero (b) addition of a drug that blocks Ca2+ binding to troponin (c) an increase in the amount of ATP in the cell (d) a mutation in tropomyosin that decreases its affinity for the actin filament
(b) addition of a drug that blocks Ca2+ binding to troponin
20-16 Proteoglycans in the extracellular matrix of animal tissues ________________. (a) chiefly provide tensile strength. (b) allow cartilage to resist compression. (c) are linked to microtubules through the plasma membrane. (d) are polysaccharides composed of glucose subunits.
(b) allow cartilage to resist compression.
20-42 A pluripotent cell _________. (a) can only be produced in the laboratory. (b) can give rise to all the tissues and cell types in the body. (c) can only give rise to stem cells. (d) is considered to be terminally differentiate
(b) can give rise to all the tissues and cell types in the body.
20-39 Cells that are terminally differentiated ______________________. (a) will undergo apoptosis within a few days. (b) can no longer undergo cell division.(c) are unable to move. (d) no longer produce RNAs.
(b) can no longer undergo cell division.
17-9 Intermediate filaments help protect animal cells from mechanical stress because ____________.(a) filaments directly extend from the interior of the cell to the extracellular space and into the next cell, linking one cell to the next, helping to distribute locally applied forces.(b) filaments in each cell are indirectly connected to the filaments of a neighboring cell through the desmosome, creating a continuous mechanical link between cells.(c) filaments remain independent of other cytoskeletal elements and keep the mechanical stress away from other cellular components.(d) filaments make up the desmosome junctions that connect cells; these junctions are more important than the internal network of filaments for protecting cells against mechanical stress.
(b) filaments in each cell are indirectly connected to the filaments of a neighboring cell through the desmosome, creating a continuous mechanical link between cells.
16-5 When a signal needs to be sent to most cells throughout a multicellular organism, the signal most suited for this is a ___________. (a) neurotransmitter. (b) hormone. (c) dissolved gas. (d) scaffold.
(b) hormone.
20-23 At desmosomes, cadherin molecules are connected to ________________. (a) actin filaments. (b) intermediate filaments. (c) microtubules. (d) gap junctions.
(b) intermediate filaments.
20-19 A basal lamina ______________________. (a) is a thin layer of connective-tissue cells and matrix underlying an epithelium. (b) is a thin layer of extracellular matrix underlying an epithelium. (c) is attached to the apical surface of an epithelium. (d) separates epithelial cells from each other.
(b) is a thin layer of extracellular matrix underlying an epithelium.
20-33 Cadherins ______________________. (a) are used to transfer proteins from one cell to another. (b) mediate cell-cell attachments through homophilic interactions. (c) are abundant in the plant cell wall.(d) bind to collagen fibrils.
(b) mediate cell-cell attachments through homophilic interactions.
6-3 The classic experiments conducted by Meselson and Stahl demonstrated that DNA replication is accomplished by employing a ________________ mechanism. (a) continuous (b) semiconservative (c) dispersive (d) conservative
(b) semiconservative
20-45 An individual that arises by reproductive cloning has a nuclear genome that is identical to __________. (a) the female who donated the egg. (b) the adult who donated the cell for nuclear transplantation. (c) both the female who donated the egg and the adult who donated the cell for nuclear transplantation. (d) the foster mother in which the embryo is placed.
(b) the adult who donated the cell for nuclear transplantation.
20-28 A major distinction between the connective tissues in an animal and other main tissue types such as epithelium, nervous tissue, or muscle is _______________. (a) the ability of connective-tissue cells such as fibroblasts to change shape. (b) the amount of extracellular matrix in connective tissues. (c) the ability of connective tissues to withstand mechanical stresses. (d) the numerous connections that connective-tissue cells make with each other.
(b) the amount of extracellular matrix in connective tissues.
20-8 Which of the following is not an example of a connective tissue? (a) bone (b) the layer of photoreceptors in the eye (c) the jellylike interior of an eye (d) cartilage
(b) the layer of photoreceptors in the eye
6-4 Initiator proteins bind to replication origins and disrupt hydrogen bonds between the two DNA strands being copied. Which of the factors below does not contribute to the relative ease of strand separation by initiator proteins? (a) replication origins are rich in A-T base pairs (b) the reaction can occur at room temperature (c) they only separate a few base pairs at a time (d) once opened, other proteins of the DNA replication machinery bind to the origin
(b) the reaction can occur at room temperature
6-12 The chromatin structure in eukaryotic cells is much more complicated than that observed in prokaryotic cells. This is thought to be the reason that DNA replication occurs much faster in prokaryotes. How much faster is it? (a) 2× (b) 5× (c) 10× (d) 100×
(c) 10×
20-52 Which of the following statements about cancer is false? (a) Viruses cause some cancers. (b) Tobacco use is responsible for more than 20% of all cancer deaths. (c) A mutation in even a single cancer-critical gene is sufficient to convert a normal cell into a cancer cell. (d) Chemical carcinogens cause cancer by changing the nucleotide sequence of DNA.
(c) A mutation in even a single cancer-critical gene is sufficient to convert a normal cell into a cancer cell.
20-30 Which of the following statements about gap junctions is false? (a) Gap junctions are made of connexons. (b) Molecules up to 1000 daltons in molecular mass can move across gap junctions. (c) Because gap junctions do not allow ions to pass through, they are not used for electrically coupling cells. (d) Gap junctions can close in response to extracellular signals.
(c) Because gap junctions do not allow ions to pass through, they are not used for electrically coupling cells.
17-40 Figure Q17-40A shows how the movement of dynein causes the flagellum to bend. If instead of the normal situation, the polarity of the adjacent doublet of microtubules were to be reversed (see Figure Q17-40B), what do you predict would happen?Figure Q17-40 (a) No bending would occur. (b) Bending would occur exactly as diagrammed in Figure Q17-40A. (c) Bending would occur, except that the right microtubule doublet would move down relative to the left one. (d) The two microtubule doublets would slide away from each other.
(c) Bending would occur, except that the right microtubule doublet would move down relative to the left one.
17-52 Figure Q17-52 shows the leading edge of a lamellipodium. Which of the following statements is false?Figure Q17-52 (a) Nucleation of new filaments near the leading edge pushes the plasma membrane forward. (b) ARP proteins nucleate the branched actin filaments in the lamellipodium. (c) Capping proteins bind to the minus end of actin filaments. (d) There is more ATP-bound actin at the leading edge than in the actin filaments away from the leading edge.
(c) Capping proteins bind to the minus end of actin filaments.Capping protein binds to the plus end of actin filaments, preventing further assembly or disassembly from the growing end.
17-53 You are examining a cell line in which activation of the Rho family member Rac promotes lamellipodia formation. Which of the following statements is most likely to be true? (a) Cells carrying a Rac mutation that makes Rac act as if it is always bound to GTP will polymerize more unbranched actin filaments than normal cells. (b) Cells carrying a Rac mutation that makes Rac unable to exchange GDP for GTP will polymerize more unbranched actin filaments than normal cells. (c) Cells carrying a Rac mutation that makes Rac act as if it is always bound to GTP will polymerize more branched actin filaments than normal cells. (d) Cells carrying a Rac mutation that makes Rac unable to exchange GDP for GTP will polymerize more branched actin filaments than normal cells.
(c) Cells carrying a Rac mutation that makes Rac act as if it is always bound to GTP will polymerize more branched actin filaments than normal cells.
17-2 Which of the following statements about the cytoskeleton is false?(a) The cytoskeleton is made up of three types of protein filaments.(b) The cytoskeleton controls the location of organelles in eukaryotic cells.(c) Covalent bonds between protein monomers hold together cytoskeletal filaments.(d) The cytoskeleton of a cell can change in response to the environment.
(c) Covalent bonds between protein monomers hold together cytoskeletal filaments.
17-15 You are studying nuclear lamins in yeast. Using recombinant DNA technology, you alter the coding sequence of a nuclear lamin gene such that the gene now codes for a nuclear lamin protein that can no longer be phosphorylated when the nuclear envelope is broken down during mitosis. What do you predict would happen if the yeast cell only had the altered nuclear lamin gene (and not the unaltered version)?(a) Mitosis should proceed as usual because the dephosphorylation of the lamin is what is important for nuclear lamina assembly during mitosis, so phosphorylation will not be necessary.(b) Disassembly of the nuclear lamins will occur prematurely because the lamins cannot be phosphorylated.(c) Nuclear lamins will no longer disassemble properly during mitosis.(d) Nuclear lamins will be unable to produce dimers, as coiled-coil formation will be disrupted.
(c) Nuclear lamins will no longer disassemble properly during mitosis.
20-17 Which of the following statements is false? (a) Proteoglycans can act as filters to regulate which molecules pass through the extracellular medium. (b) The negative charge associated with proteoglycans attracts cations, which cause water to be sucked into the extracellular matrix. (c) Proteoglycans are a major component of compact connective tissues but are relatively unimportant in watery tissues such as the jellylike substance in the interior of the eye. (d) Glycosaminoglycans are components of proteoglycan.
(c) Proteoglycans are a major component of compact connective tissues but are relatively unimportant in watery tissues such as the jellylike substance in the interior of the eye.
20-57 Ras is a GTP-binding protein that is often defective in cancer cells. A common mutation found in cancer cells causes Ras to behave as though it were bound to GTP all the time, which will cause cells to divide inappropriately. From this description, the normal Ras gene is _______. (a) a tumor suppressor. (b) an oncogene. (c) a proto-oncogene. (d) a gain-of-function mutation.
(c) a proto-oncogene.
20-21 Tight junctions ______________________.( a) allow small, water-soluble molecules to pass from cell to cell. (b) interact with the intermediate filaments inside the cell. (c) are formed from claudins and occludins. (d) are found in cells in connective tissues.
(c) are formed from claudins and occludins.
20-41 An adult hemopoietic stem cell found in the bone marrow ______________________. (a) will occasionally produce epidermal cells when necessary. (b) can produce only red blood cells. (c) can undergo self-renewing divisions for the lifetime of a healthy animal. (d) will express all the same transcription factors as those found in an unfertilized egg.
(c) can undergo self-renewing divisions for the lifetime of a healthy animal.
6-2 DNA replication is considered semiconservative because ____________________________. (a) after many rounds of DNA replication, the original DNA double helix is still intact. (b) each daughter DNA molecule consists of two new strands copied from the parent DNA molecule. (c) each daughter DNA molecule consists of one strand from the parent DNA molecule and one new strand. (d) new DNA strands must be copied from a DNA template.
(c) each daughter DNA molecule consists of one strand from the parent DNA molecule and one new strand.
20-35 The plasmodesmata in plants are functionally most similar to which animal cell junction? (a) tight junction (b) adherens junction (c) gap junction (d) desmosome
(c) gap junction
17-35 Which of the following statements is correct? Kinesins and dyneins ____________________. (a) have tails that bind to the filaments. (b) move along both microtubules and actin filaments. (c) often move in opposite directions to each other. (d) derive their energy from GTP hydrolysis.
(c) often move in opposite directions to each other.
17-56 Which of the following structures shorten during muscle contraction? (a) myosin filaments (b) flagella (c) sarcomeres (d) actin filaments
(c) sarcomeres
17-24 The microtubules in a cell form a structural framework that can have all the following functions except which one?(a) holding internal organelles such as the Golgi apparatus in particular positions in the cell(b) creating long, thin cytoplasmic extensions that protrude from one side of the cell(c) strengthening the plasma membrane(d) moving materials from one place to another inside a cell
(c) strengthening the plasma membrane
6-1 The process of DNA replication requires that each of the parental DNA strands be used as a ___________________ to produce a duplicate of the opposing strand. (a) catalyst (b) competitor (c) template (d) copy
(c) template
20-32 Which type of junction contributes the most to the polarization of epithelial cells? (a) adherens junctions (b) desmosomes (c) tight junctions (d) gap junctions
(c) tight junctions
6-10 How does the total number of replication origins in bacterial cells compare with the number of origins in human cells? (a) 1 versus 100 (b) 5 versus 500 (c) 10 versus 1000 (d) 1 versus 10,000
(d) 1 versus 10,000
17-4 Which of the following statements about the cytoskeleton is true?(a) All eukaryotic cells have actin, microtubules, and intermediate filaments in their cytoplasm.(b) The cytoskeleton provides a rigid and unchangeable structure important for the shape of the cell.(c) The three cytoskeletal filaments perform distinct tasks in the cell and act completely independently of one another.(d) Actin filaments and microtubules have an inherent polarity, with a plus end that grows more quickly than the minus end.
(d) Actin filaments and microtubules have an inherent polarity, with a plus end that grows more quickly than the minus end.
17-63 Consider the in vitro motility assay using purified kinesin and purified polymerized microtubules shown in Figure Q17-63. The three panels are images taken at 1-second intervals. In this figure, three microtubules have been numbered to make it easy to identify them. Which of the following statements about this assay is false?Figure Q17-63 (a) Kinesin molecules are attached by their tails to a glass slide. (b) The microtubules used in this assay must be polymerized using conditions that stabilize tubule formation or else they would undergo dynamic instability. (c) ATP must be added for this assay to work. (d) Addition of the nonhydrolyzable ATP analog (AMP-PNP) would cause the microtubules to move faster.
(d) Addition of the nonhydrolyzable ATP analog (AMP-PNP) would cause the microtubules to move faster.
6-5 If the genome of the bacterium E. coli requires about 20 minutes to replicate itself, how can the genome of the fruit fly Drosophila be replicated in only 3 minutes? (a) The Drosophila genome is smaller than the E. coli genome. (b) Eukaryotic DNA polymerase synthesizes DNA at a much faster rate than prokaryotic DNA polymerase. (c) The nuclear membrane keeps the Drosophila DNA concentrated in one place in the cell, which increases the rate of polymerization. (d) Drosophila DNA contains more origins of replication than E. coli DNA.
(d) Drosophila DNA contains more origins of replication than E. coli DNA.
17-6 Which of the statements below about intermediate filaments is false?(a) They can stay intact in cells treated with concentrated salt solutions.(b) They can be found in the cytoplasm and the nucleus.(c) They can be anchored to the plasma membrane at a cell-cell junction.(d) Each filament is about 10 μm in diameter.
(d) Each filament is about 10 μm in diameter.
20-44 How do reproductive cloning and therapeutic cloning differ? (a) The DNA in the nucleus of cells produced for therapeutic cloning is genetically identical to the donor genome, whereas in cells produced for reproductive cloning it is not. (b) Reproductive cloning requires a supply of fertilized donor egg cells, whereas therapeutic cloning requires unfertilized egg cells. (c) Therapeutic cloning requires nuclear transplantation, whereas reproductive cloning does not. (d) Embryos are placed into foster mothers during reproductive cloning but not during therapeutic cloning.
(d) Embryos are placed into foster mothers during reproductive cloning but not during therapeutic cloning.
20-6 Which of the following statements about cellulose is false? (a) Cellulose synthase enzyme complexes are integral membrane proteins. (b) An array of microtubules guides the cellulose synthase complex as it moves in the membrane. (c) The sugar monomers necessary for the synthesis of a cellulose polymer are transported across the plasma membrane. (d) Microtubules are directly attached to the outside surface of the plasma membrane to form tracks that help orient the cellulose polymers.
(d) Microtubules are directly attached to the outside surface of the plasma membrane to form tracks that help orient the cellulose polymers.
17-13 Keratins, neurofilaments, and vimentins are all categories of intermediate filaments. Which of the following properties is not true of these types of intermediate filaments?(a) They strengthen cells against mechanical stress.(b) Dimers associate by noncovalent bonding to form a tetramer.(c) They are found in the cytoplasm.(d) Phosphorylation causes disassembly during every mitotic cycle.
(d) Phosphorylation causes disassembly during every mitotic cycle.
20-9 Which of the following statements about animal connective tissues is true?(a) Enzymes embedded in the plasma membrane synthesize the collagen in the extracellular matrix extracellularly.(b) In connective tissue, the intermediate filaments within the cells are important for carrying the mechanical load. (c) Cells can attach to a collagen matrix by using fibronectin, an integral membrane protein. (d) Proteoglycans can resist compression in the extracellular matrix.
(d) Proteoglycans can resist compression in the extracellular matrix.
17-50 Cell movement involves the coordination of many events in the cell. Which of the following phenomena is not required for cell motility? (a) Myosin-mediated contraction at the rear of the moving cell. (b) Integrin association with the extracellular environment. (c) Nucleation of new actin filaments. (d) Release of Ca2+ from the sarcoplasmic reticulum.
(d) Release of Ca2+ from the sarcoplasmic reticulum.
17-33 Microtubules are important for transporting cargo in nerve cell axons, as diagrammed in Figure Q17-33. Notice that the two types of cargo are traveling in opposite directions. Which of the following statements is likely to be false?Figure Q17-33 (a) The gray cargo is attached to dynein. (b) The black cargo and the gray cargo require ATP hydrolysis for their motion. (c) The black cargo moving toward the axon terminal contains a domain that specifically interacts with the tail domain of a particular kind of motor. (d) The black cargo and the gray cargo are moving along microtubules of opposite polarity.
(d) The black cargo and the gray cargo are moving along microtubules of opposite polarity.
17-42 Which of the following statements about actin is false? (a) ATP hydrolysis decreases actin filament stability. (b) Actin at the cell cortex helps govern the shape of the plasma membrane. (c) Actin filaments are nucleated at the side of existing actin filaments in lamellipodia. (d) The dynamic instability of actin filaments is important for cell movement.
(d) The dynamic instability of actin filaments is important for cell movement.
17-28 Which of the following statements regarding dynamic instability is false?(a) Each microtubule filament grows and shrinks independently of its neighbors. (b) The GTP cap helps protect a growing microtubule from depolymerization. (c) GTP hydrolysis by the tubulin dimer promotes microtubule shrinking. (d) The newly freed tubulin dimers from a shrinking microtubule can be immediately captured by growing microtubules and added to their plus end.
(d) The newly freed tubulin dimers from a shrinking microtubule can be immediately captured by growing microtubules and added to their plus end.
6-11 Which of the following statements correctly explains what it means for DNA replication to be bidirectional? (a) The replication fork can open or close, depending on the conditions. (b) The DNA replication machinery can move in either direction on the template strand. (c) Replication-fork movement can switch directions when the fork converges on another replication fork. (d) The replication forks formed at the origin move in opposite directions.
(d) The replication forks formed at the origin move in opposite directions.
17-16 You are interested in understanding the regulation of nuclear lamina assembly. To create an in vitro system for studying this process you start with partly purified nuclear lamina subunits to which you will add back purified cellular components to drive nuclear lamina assembly. Before you start doing experiments, your instructor suggests that you consider what type of conditions would be most amenable to the assembly of the nuclear lamina from its individual subunits in vitro. Which of the following conditions do you predict would be most likely to enhance the assembly of the nuclear lamina?(a) addition of phosphatase inhibitors(b) addition of ATP(c) addition of a concentrated salt solution that is 10 times the concentration normally found in the nucleoplasm(d) addition of protein kinase inhibitors
(d) addition of protein kinase inhibitors
17-23 The hydrolysis of GTP to GDP carried out by tubulin molecules ________________.(a) provides the energy needed for tubulin to polymerize.(b) occurs because the pool of free GDP has run out.(c) tips the balance in favor of microtubule assembly.(d) allows the behavior of microtubules called dynamic instability.
(d) allows the behavior of microtubules called dynamic instability.
20-24 Hemidesmosomes are important for ______________________. (a) tubulation of epithelial sheets. (b) linkages to glycosaminoglycans. (c) forming the basal lamina. (d) attaching epithelial cells to the extracellular matrix.
(d) attaching epithelial cells to the extracellular matrix.
20-43 Mouse embryonic stem (ES) cells ______________________. (a) can only be produced through therapeutic cloning. (b) can give rise to all tissues and cell types in the body except germ cells. (c) can be implanted in foster mothers to produce cloned cows and other animals. (d) come from the inner cell mass of early embryos.
(d) come from the inner cell mass of early embryos.
17-45 For both actin and microtubule polymerization, nucleotide hydrolysis is important for ______. (a) stabilizing the filaments once they are formed. (b) increasing the rate at which subunits are added to the filaments. (c) promoting nucleation of filaments. (d) decreasing the binding strength between subunits on filaments.
(d) decreasing the binding strength between subunits on filaments.
20-50 A malignant tumor is more dangerous than a benign tumor because ______________________. (a) its cells are proliferating faster. (b) it causes neighboring cells to mutate. (c) its cells attack and phagocytose neighboring normal tissue cells. (d) its cells invade other tissues.
(d) its cells invade other tissues.
Use the following information about a series of in vitro DNA replication experiments to answer questions 6-16 through 6-22.You prepare bacterial cell extracts by lysing the cells and removing insoluble debris via centrifugation. These extracts provide the proteins required for DNA replication. Your DNA template is a small, double-stranded circular piece of DNA (a plasmid) with a single origin of replication and a single replication termination site. The termination site is on the opposite side of the plasmid from the origin.6-19 What part of the DNA replication process would be most directly affected if a strain of bacteria lacking the exonuclease activity of DNA polymerase were used to make the cell extracts? (a) initiation of DNA synthesis (b) Okazaki fragment synthesis (c) leading-strand elongation (d) lagging-strand completion
(d) lagging-strand completion
17-55 Your friend works in a biotech company that has just discovered a drug that seems to promote lamellipodia formation in cells. Which of the following molecules is unlikely to be involved in the pathway that this drug affects? (a) Rac (b) ARP (c) actin (d) myosin
(d) myosin
20-12 Fibroblasts organize the collagen of the extracellular matrix by ______________.(a) cutting and rejoining the fibrils. (b) processing procollagen into collagen. (c) twisting fibrils together to make ropelike fibers. (d) pulling the collagen into sheets or cables after it has been secreted.
(d) pulling the collagen into sheets or cables after it has been secreted.
20-1 Both multicellular plants and animals have _____________________. (a) cells capable of locomotion. (b) cells with cell walls. (c) a cytoskeleton composed of actin filaments, microtubules, and intermediate filaments. (d) tissues composed of multiple different cell types.
(d) tissues composed of multiple different cell types.plant cells don't have intermediate filaments
20-47 The artificial introduction of three key ______________ into an adult cell can convert the adult cell into a cell with the properties of ES cells. (a) chromosomes (b) viruses (c) hormones (d) transcription factors
(d) transcription factors
17-19 Which of the following statements about the structure of microtubules is false?(a) Microtubules are built from protofilaments that come together to make a hollow structure.(b) The two ends of a protofilament are chemically distinct, with α-tubulin exposed at one end and β-tubulin exposed at the other end.(c) Within a microtubule, all protofilaments are arranged in the same orientation, giving the microtubule structural polarity.(d) α-Tubulin and β-tubulin are covalently bound to make the tubulin dimer that then assembles into protofilaments.
(d) α-Tubulin and β-tubulin are covalently bound to make the tubulin dimer that then assembles into protofilaments.
17-11 For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below. Not all words or phrases will be used; use each word or phrase only once.Intermediate filaments are found mainly in cells that are subject to mechanical stress. Gene mutations that disrupt intermediate filaments cause some rare human genetic diseases. For example, the skin of people with epidermolysis bullosa simplex is very susceptible to mechanical injury; people with this disorder have mutations in their __________________ genes, which code for the intermediate filament found in epithelial cells. These filaments are usually connected from cell to cell through junctions called __________________s. The main filaments found in muscle cells belong to the __________________ family; people with disruptions in these intermediate filaments can have muscular dystrophy. In the nervous system, __________________s help strengthen the extremely long extensions often present in nerve cell axons; disruptions in these intermediate filaments can lead to neurodegeneration. People who carry mutations in the gene for __________________, an important protein for cross-linking intermediate filaments, have a disease that combines symptoms of epidermolysis bullosa simplex, muscular dystrophy, and neurodegeneration. Humans with progeria, a disease that causes premature aging, carry mutations in a nuclear ____________.desmosome lamin synapsekeratin neurofilament vimentinkinase plectin
17-11 Intermediate filaments are found mainly in cells that are subject to mechanical stress. Gene mutations that disrupt intermediate filaments cause some rare human genetic diseases. For example, the skin of people with epidermolysis bullosa simplex is very susceptible to mechanical injury; people with this disorder have mutations in their keratin genes, the intermediate filament found in epithelial cells. These filaments are usually connected from cell to cell through junctions called desmosomes. The main filaments found in muscle cells belong to the vimentin family; people with disruptions in these intermediate filaments can have muscular dystrophy. In the nervous system, neurofilaments help strengthen the extremely long extensions often present in nerve cell axons; disruptions in these intermediate filaments can lead to neurodegeneration. People who carry mutations in the gene for plectin, an important protein for cross-linking intermediate filaments, have a disease that combines symptoms of epidermolysis bullosa simplex, muscular dystrophy, and neurodegeneration. Humans with progeria, a disease that causes premature aging, carry mutations in a nuclear lamin.
17-22 For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below. Not all words or phrases will be used; use each word or phrase only once.Microtubules are formed from the tubulin heterodimer, which is composed of the nucleotide-binding __________________ protein and the __________________ protein. Tubulin dimers are stacked together into protofilaments; __________________ parallel protofilaments form the tubelike structure of a microtubule. __________________ rings are important for microtubule nucleation and are found in the __________________ , which is usually found near the cell's nucleus in cells that are not undergoing mitosis. A microtubule that is quickly growing will have a __________________ cap that helps prevent the loss of subunits from its growing end. Stable microtubules are used in cilia and flagella; these microtubules are nucleated from a __________________ and involve a "__________________ plus two" array of microtubules. The motor protein __________________ generates the bending motion in cilia; the lack of this protein can cause Kartagener's syndrome in humans.α-tubulin dynein nineATP four thirteenbasal body γ-tubulin twenty-oneβ-tubulin GTP UTPcentrosome kinesin two vimentinδ-tubulin myosin
17-22 Microtubules are formed from the tubulin heterodimer, which is composed of the nucleotide-binding β-tubulin protein and the α-tubulin protein. Tubulin dimers are stacked together into protofilaments; thirteen parallel protofilaments form the tubelike structure of a microtubule. γ-Tubulin rings are important for microtubule nucleation and are found in the centrosome, which is usually found near the cell's nucleus in cells that are not undergoing mitosis. A microtubule that is quickly growing will have a GTP cap that helps prevent the loss of subunits from its growing end. Stable microtubules are used in cilia and flagella; these microtubules are nucleated from a basal body and involve a "nine plus two" array of microtubules. The motor protein dynein generates the bending motion in cilia; the lack of this protein can cause Kartagener's syndrome in humans.
17-7 For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below. Not all words or phrases will be used; use each word or phrase only once.Intermediate filaments are elongated fibrous proteins with an N-terminal globular _________________ region and a C-terminal globular _________________ region; these regions flank the elongated rod domain. The α-helical region of the rod interacts with the α-helical region of another monomer in a _____________________ configuration to form a dimer. ______________ dimers will line up to form a staggered tetramer. ______________ strands of tetramers come together and twist together to form the _________________ nm filament. The ___________________ domains are exposed on the surface of the intermediate filament, allowing for interaction with cytoplasmic components.antiparallel four tailβ barrel globular tencoiled-coil head trimericcovalent rod twenty-fiveeight seven two
17-7 Intermediate filaments are elongated fibrous proteins with an N-terminal globular head region and a C-terminal globular tail region; these regions flank the elongated rod domain. The α-helical region of the rod interacts with the α-helical region of another monomer in a coiled-coil configuration to form a dimer. Two dimers will line up to form a staggered tetramer. Eight strands of tetramers come together and twist together to form the ten nm filament. The globular domains are exposed on the surface of the intermediate filament, allowing for interaction with cytoplasmic components.
20-13 Match the four lettered lines in Figure Q20-13 with the appropriate numbered label. Figure Q20-13 1. integrin 2. actin 3. collagen 4. fibronectin
20-13 A—3; B—4; C—1; D—2
20-2 For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below. Not all words or phrases will be used; use each word or phrase only once.Plants are sedentary and thus their cells have different needs from those of cells found in motile animals. For example, in plant cells, __________________ generates the turgor pressure that drives cell growth. Plants have cell walls, but cell growth is possible in the developing tissue because the __________________ cell walls are expandable. The __________________ cell walls are deposited once growth has stopped, and can be specially adapted to their function. Fibers made from __________________ (the most abundant organic macromolecule on Earth) are found in plant cell walls, and provide tensile strength. In woody tissues, the __________________ in the cell walls makes the tissue more rigid and waterproof. The deposition of the cell wall is directed by the __________________ cytoskeleton.actin lignin pectincellulose membranous primarycollagen microtubule secondaryepidermis nuclear tertiarylamin osmosis
20-2 Plants are sedentary and thus their cells have different needs from those of cells found in motile animals. For example, in plant cells, osmosis generates the turgor pressure that drives cell growth. Plants have cell walls, but cell growth is possible in the developing tissue because the primary cell walls are expandable. The secondary cell walls are deposited once growth has stopped, and can be specially adapted to their function. Fibers made from cellulose (the most abundant organic macromolecule on Earth) are found in plant cell walls, and provide tensile strength. In woody tissues, the lignin in the cell walls makes the tissue more rigid and waterproof. The deposition of the cell wall is directed by the microtubule cytoskeleton.
20-25 For each of the following sentences, fill in the blanks with the best word or phrase selected from the list below. Not all words or phrases will be used; use each word or phrase only once.__________________ join the intermediate filaments in one cell to those in the neighboring cell. __________________ anchor intermediate filaments in a cell to the extracellular matrix. __________________ involve cadherin connections between neighboring cells and are anchorage sites for actin filaments. __________________ permit the passage of small molecules from one cell to its adjacent cell. __________________ prevent the leakage of molecules between adjacent cells.adherens junctions gap junctions highway junctionsdesmosomes hemidesmosomes tight junctions
20-25 Desmosomes join the intermediate filaments in one cell to those in the neighboring cell. Hemidesmosomes anchor intermediate filaments in a cell to the extracellular matrix. Adherens junctions involve cadherin connections between neighboring cells and are anchorage sites for actin filaments. Gap junctions permit the passage of small molecules from one cell to its adjacent cell. Tight junctions prevent the leakage of molecules between adjacent cells.
17-43 Actin can adopt a variety of shapes. Match the name of the actin form with the type of actin structure depicted as black lines within the cells in Q17-43._____ lamellipodia_____ contractile bundles_____ contractile ring_____ microvilli
__C__ lamellipodia__B__ contractile bundles__D__ contractile ring__A__ microvilli
20-14 A cell can crawl through a tissue because of the transmembrane ______________ proteins that can bind to fibronectin outside of the cell. (a) integrin (b) collagen (c) gap junction (d) claudin
a) integrin
20-20 Match the labeled parts of Figure Q20-20 with the phrase that best matches the part. Each part will only be used once.Figure Q20-20basal lamina ______apical surface _______cell junction _______connective tissue _______
basal lamina ___B___apical surface ___A____cell junction ___C____connective tissue ___D____
20-10 Do you agree or disagree with the following statement? Explain your answer.Like many other extracellular proteins, newly synthesized collagen molecules undergo post-translational processing inside the cell to convert them into their mature form; they are then secreted and self-assemble into fibrils in the extracellular space.
false
