cell bio section 3 practice/quiz questions
A fibroblast can attach indirectly to collagen via which type of extracellular matrix protein? A. fibronectin B. elastins C. cadherins D. glycosaminoglycans
A
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
Consider the process that a cell uses to replicate its double-stranded DNA before undergoing cell division. Which statement describes the DNA in the resulting daughter cells? A. The double helix in each daughter cell consists of one parental strand and one newly synthesized strand. B. The daughter cells receive only newly synthesized DNA; the parent cell keeps the original DNA. C. Each strand of DNA in the daughter cells contains a mix of both newly replicated and parental DNA. D. The double helix in one daughter cell consists of two strands that were originally in the parent cell, while the double helix in the other daughter cell consists of two newly made strands. E. Each daughter cell receives a random mix of parental chromosomes and new chromosomes.
A
How would the animation of microtubule dynamics change after adding a non-hydrolyzable analog of GTP to the cells expressing GFP tubulin? A. Microtubules would grow longer. B. Microtubules would shrink. C. Dynamic instability would increase as microtubules rapidly switch between growing and shrinking. D. Microtubule dynamics would not change.
A
In most respects, cell division is similar between plant and animal cells. Which of the following events occurs by a different mechanism in animal and plant cells? A. separation of the cell into two daughter cells B. condensation of chromosomes at the beginning of cell division C. alignment of chromosomes in the center of the cell D. chromosomes being pulled apart by the microtubules of the mitotic spindle E. separation of sister chromatids
A
In which direction does a plant cell elongate? A. perpendicular to the orientation of the cellulose microfibrils B. parallel to the orientation of the cellulose microfibrils C. toward the sun and away from the Earth
A
Latrunculins are toxins produced by certain sponges that bind to the monomers used by Listeria and thus block filament polymerization. How would adding Latrunculin A to a Listeria-infected cell affect Listeria motility? A. The Listeria would have decreased motility because filament polymerization is required for movement. B. The Listeria would have decreased motility because filaments are required for synthesizing the motility proteins. C. The Listeria would have increased motility because filament polymerization blocks Listeria movement. D. The Listeria would have increased motility because more subunits would be free as monomers to push the Listeria forward.
A
Mutations in genes encoding cell signaling proteins contribute to many cancers. For example, a chromosomal translocation fuses the Bcr gene to the Abl gene, leading to a constitutively active Bcr-Abl kinase and chronic myeloid leukemia (CML). CML is successfully treated with the drug imatinib (trade name Gleevec), which mimics an Abl kinase substrate and thus inhibits kinase activity. What normal cell molecule, and kinase substrate, does Gleevec mimic? A. ATPPi (inorganic phosphate) B. ADP C. cAMP
A
Programmed cell death occurs... A. by means of an intracellular suicide program. B. rarely and selectively only during animal development. C. only in unhealthy or abnormal cells. D. only during embryonic development.
A
Rb is an important protein for controlling cell proliferation by blocking entry into S phase. How does it exert its effect? A. In its unphosphorylated state, Rb is active and blocks transcriptional regulators. B. Signaling through mitogen-activated pathways activates Rb kinase activity. C. When phosphorylated by G1-Cdk, Rb binds to DNA and activates transcription. D. In its phosphorylated state, Rb is active and blocks G1-Cdk activity.
A
Sister chromatid separation occurs because __________ are destroyed by the APC/C. A. securins B. cohesins C. kinetochores D. condensins
A
Sometimes, chemical damage to DNA can occur just before DNA replication begins, not giving the repair system enough time to correct the error before the DNA is duplicated. This gives rise to mutation. If the cytosine in the sequence TCAT is deaminated and not repaired, which of the following is the point mutation you would observe after this segment has undergone two rounds of DNA replication? A. TTAT B. TUAT C. TGAT D. TAAT
A
The anaphase-promoting complex or cyclosome (APC/C) triggers the onset of anaphase by doing which of the following? A. triggering the destruction of the cohesins that hold the sister chromatids together B. phosphorylating the motor proteins that pull the spindle poles apart C. triggering the destruction of the condensins that hold the duplicated chromosomes in a condensed state D. cleaving spindle microtubules
A
What does the phosphorylation of Cdc25 by M-Cdk do? A. It activates Cdc25, which in turn activates more M-Cdk. B. It activates Cdc25, which inactivates M-Cdk. C. It inactivates Cdc25, which promotes activation of more M-Cdk. D. It inactivates Cdc25, preventing further activation of M-Cdk. E. It activates Cdc25, allowing the cell to exit mitosis.
A
Which of the following occurs at specific times in the cell cycle? A. some cyclins are ubiquitylated and degraded in proteasomes. B. Some Cdks are ubiquitylated and degraded in proteasomes. C. Some Cdks are phosphorylated and degraded in proteasomes. D. Some cyclins are methylated and degraded in proteasomes.
A
Which of the following statements about molecular switches is FALSE? A. Phosphatases remove the phosphate from GTP on GTP-binding proteins, turning them off. B. Protein kinases transfer the terminal phosphate from ATP onto a protein. C. Serine/threonine kinases are the most common types of protein kinase. D. A GTP-binding protein exchanges its bound GDP for GTP to become activated.
A
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 ã-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
Which of the following statements is true? A. Ion-channel-coupled receptors can rapidly alter the membrane potential in response to signal binding. B. Many ion-channel-coupled receptors have an intrinsic catalytic domain on the cytosolic side of the plasma membrane. C. G-protein-coupled receptors are GTP-binding proteins. D. All enzyme-coupled receptors have an intrinsic catalytic domain on the cytosolic side of the plasma membrane. E. Each extracellular signal molecule interacts with a single class of cell-surface receptor.
A
Which statement about cell signaling is correct? A. Each receptor is generally activated by only one type of signal molecule. B. All cell types are able to respond to the same set of signal molecules. C. Each type of extracellular signal molecule induces the same response in all target cells. D. Each receptor triggers one particular type of cell behavior, for example, activating gene expression. E. All extracellular signal molecules act by binding to receptors on the cell surface.
A
Which of the following would increase the level of muscle contraction? Choose one or more: A. addition of a leaky Ca2+ channel to the sarcoplasmic reticulum B. blockage of the Ca2+ pump C .addition of a molecule to bind free Ca2+ D. mutation in troponin such that it no longer binds tropomyosin
A and B
For both clinical and cosmetic reasons, plastic surgeons inject substances into connective tissue underlying the skin epidermis. This plumps up areas deficient in soft tissue, and is used to reduce surgical scars or wrinkles, for example. Which normal connective tissue components are good candidates to be injected as fillers in this type of procedure? Choose one or more: A.glycosaminoglycan B.cadherin C.collagen D.hemidesmosome
A and C
Most extracellular signal molecules act on cell-surface receptors rather than intracellular receptors. Which statements are true about these extracellular molecules? Choose one or more: A. They are too hydrophilic to pass directly across the plasma membrane. B. They are too small to pass directly across the plasma membrane. C. They are too hydrophobic to pass directly across the plasma membrane. D. They are too large to pass directly across the plasma membrane.
A and D
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
Acetylcholine is a signaling molecule that elicits responses from heart muscle cells, salivary gland cells, and skeletal muscle cells. Which of the following statements is FALSE? A. Heart muscle cells decrease their rate and force of contraction when they receive acetylcholine, whereas skeletal muscle cells contract. B. Heart muscle cells, salivary gland cells, and skeletal muscle cells all express an acetylcholine receptor that belongs to the transmitter-gated ion channel family. C. Active acetylcholine receptors on salivary gland cells and heart muscle cells activate different intracellular signaling pathways. D. Heart muscle cells, salivary gland cells, and skeletal muscle cells all respond to acetylcholine within minutes of receiving the signal.
B
An experiment was performed to determine the role that ATP plays in kinesin movement along microtubules. Kinesin and microtubules were incubated together in a test tube, but instead of ATP, a non-hydrolyzable analog of ATP was added to the tube. What impact on kinesin function do you expect to observe in the presence of this ATP analog? A. The leading head would bind tightly, but the trailing head would remain free. B. The kinesin would bind tightly to microtubules and not release. C. The kinesin would walk faster along the microtubule since the kinesin would remain active while bound to ATP. D. The kinesin would be unable to bind to microtubules since the kinesin would remain inactive.
B
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
Determine whether the following statement is true or false and why:Homologous recombination occurs only between DNA molecules that are identical in nucleotide sequence without any variation. A. true, but only for cells that have more than 10 chromosomes B. false, because only similar sequence is needed C. false, because crossing-over does not happen D. true, for all eukaryotic diploid cells
B
GTP hydrolysis and whether GTP or GDP is bound to tubulin is an important mechanism to control the dynamic instability of microtubules. Certain aspects of dynamic instability can be viewed using GFP-EB1. Which process(es) is it useful for visualizing and why? A. shrinking microtubules, because EB1 binds to the GTP-tubulin cap on microtubules B. growing microtubules, because EB1 binds to the GTP-tubulin cap on microtubules C. growing and shrinking microtubules, because EB1 binds to the GTP-tubulin cap on microtubules D. growing and shrinking microtubules, because EB1 binds to the GDP-tubulin cap on microtubules
B
In the absence of repair, what would the replication of a double helix containing a mismatch yield? A. one DNA molecule with the normal sequence and one DNA molecule with a mismatch B. one DNA molecule with the normal sequence and one DNA molecule with a mutated sequence C. two DNA molecules with a mutated sequence D. two DNA molecules containing different mismatches at the site of the original error E. two DNA molecules containing the mismatch
B
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
Stem cells hold great promise both for studying cell fate determination and organ development and for clinical use, such as blood stem cell transplants to treat patients whose own immune systems have been severely impaired. Clinicians also hope that stem cells can be coaxed into specific cell types to treat diseases in which that cell type is damaged, such as replacing neurons in Parkinson's disease. In 2008, researchers assessed the ability of neurons derived from reprogrammed fibroblasts to ameliorate the symptoms of Parkinson's disease in a rat model. Based on your knowledge of stem cells and cell differentiation, what intermediate step was necessary to convert fibroblasts into neurons? A. converting fibroblasts into embryonic stem cells via introduction of transcription factors B. converting fibroblasts into induced pluripotent stem cells C. converting fibroblasts into embryonic stem cells via introduction of tumor suppressor genes D. converting fibroblasts into organoids in culture
B
The Retinoblastoma (Rb) protein blocks cells from entering the cell cycle by... A. phosphorylating Cdk. B. inhibiting cyclin transcription. C. marking cyclins for destruction by proteolysis. D. activating apoptosis.
B
The bacteria Listeria monocytogenes move in and between host cells using a comet-like tail. Which of the following accurately describes Listeria motility? A. Depolymerization of host actin filaments creates passageways for the Listeria to swim through using their flagella. B. Polymerization of host actin subunits creates a comet-like tail of filaments that pushes the cell forward. C. Depolymerization of host microtubule filaments creates passageways for the Listeria to swim through using their flagella. D. Polymerization of host microtubule subunits creates a comet-like tail of filaments that pushes the cell forward.
B
The energy for DNA polymerization is provided by the hydrolysis of which of the following? A. GTP (releasing Pi) B. incoming nucleoside triphosphates (releasing PPi) C. pyrophosphate (releasing Pi) D. the 3' end of the growing strand (releasing H2O) E. ATP (releasing Pi)
B
What attaches epithelial cells to the basal lamina? A. tight junctions B. hemidesmosomes C. desmosomes D. cadherins E. adherens junctions
B
What is true of the GTP-binding proteins that act as molecular switches inside cells? A. They are active when GDP is bound. B. They are active when GTP is bound. C. They turn themselves on by phosphorylating GDP to form GTP. D. They turn themselves on by hydrolyzing GTP to form GDP. E. They are active only in their trimeric forms.
B
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
Which of the following animal tissues is characterized by a plentiful extracellular matrix? A. nervous B. connective C. muscular D. epithelial
B
Which of the following statements about plant cell walls is TRUE? A. The molecular components of the cell wall are the same in all plant tissues. B. The microtubule cytoskeleton directs the orientation in which cellulose is deposited in the cell wall. 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.
B
Which of the following statements about the cell-cycle control system is not true? A. It ensures that the environment is favorable for the cell to initiate DNA replication. B. It ensures that M phase is completed before cytokinesis begins. C. It ensures that all chromosomes are attached to the mitotic spindle before the chromosomes are segregated to the two daughter cells. D. It ensures that all DNA is replicated before M phase begins.
B
Which of the following statements is NOT an accurate statement about thymine dimers? A. Thymine dimers can cause the DNA replication machinery to stall. B. Thymine dimers are covalent links between thymidines on opposite DNA strands. C. Prolonged exposure to sunlight causes thymine dimers to form. D. Repair proteins recognize thymine dimers as a distortion in the DNA backbone.
B
An actin filament undergoing treadmilling at the leading edge of a lamellipodium can do what? A. add actin monomers to its minus end while losing them from its plus end B. experience exponential growth C. remain the same size D. collapse and instantly disappear
C
Cancer cells often lack normal DNA damage response and cell-cycle control mechanisms. Why does this make them more susceptible to DNA-damaging chemotherapies? A. Cancer cells will arrest in the cycle and will not grow further. B. Cancer cells have the ability to repair the DNA properly and thus will not accumulate mutations as quickly. C. Cancer cells might ignore the normal mechanisms that halt the cell cycle in response to damage, and subsequent division with damage leads to death. D. Cancer cells with activating mutations in Ras will amplify the damage through the Ras signaling pathway.
C
Hemopoietic stem cells in the bone marrow produce all of the following specialized cells EXCEPT... A. neutrophils. B. osteoclasts. C. heart muscle cells. D. red blood cells.
C
How is β-catenin involved in cancer? A. It is a tumor suppressor because overactivation of both copies of Brca1 or Brca2 allows cancer cells to ignore cell-cycle checkpoints. B. It is a proto-oncogene because mutations in β-catenin make the protein more active in its association with DNA polymerase during S phase. C. It is a proto-oncogene because mutations in β-catenin make the protein resistant to degradation, promoting cell proliferation. D. It is a tumor suppressor because the inactivation of both copies of it allows cancer cells to continue to survive and divide, even in the presence of damaged DNA.
C
In the intestine, what do Wnt proteins promote? A. apoptosis of the stem cells at the base of each intestinal crypt B. apoptosis of precursor cells in each intestinal crypt C. proliferation of the stem cells and precursor cells at the base of each intestinal crypt D secretion of mucus at the base of each intestinal crypt
C
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/an... A. tumor suppressor. B. oncogene. C. proto-oncogene. D. gain-of-function mutation.
C
The cell-cycle control system uses Cdk inhibitory proteins to do what? A. degrade cyclins B. degrade Cdks C. arrest the cell cycle at specific transition points D. trigger different phases of the cell cycle
C
The concentration of mitotic cyclin (M cyclin).... A. rises markedly during M phase. B. is activated by phosphorylation. C. falls toward the end of M phase as a result of ubiquitylation and degradation. D. is highest in G1 phase.
C
The drug Taxol binds tightly to microtubules and prevents them from depolymerizing. The drug colchicine binds tightly to free tubulin and prevents its polymerization into microtubules. Which of these drugs arrests cell division? A. Taxol only B. colchicine only C. both colchicine and Taxol
C
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
The shortening and thickening of chromosomes in M phase depends on which of the following? A. actin and myosin B. microtubules C. condensins D. cohesins
C
What is a major problem with using foreign cells grown in culture for transplantation in humans? A. Such cells would tend to form cancers. B. Such cells would not successfully integrate into host tissue. C. The host immune system would destroy such cells. D. Such cells would die immediately upon their removal from culture.
C
What is the name of the thin, sheetlike structures that a fibroblast regularly extends during cell crawling? A. phagosomes B. filopodia C. lamellipodia D. pseudopods
C
Which is not part of the replication machine? A. single-strand DNA-binding protein B. DNA polymerase C. DNA topoisomerase D. DNA helicase E. DNA primase
C
Which of the following molecules is NOT found in plants? A. cellulose B. lignin C. collagen D. pectin
C
Which of the following structures shorten during muscle contraction? A. myosin filaments B. flagella C. sarcomeres D. actin filaments
C
Knowledge of the driver mutations underlying cancer has led to targeted therapeutics, such as the protein kinase inhibitor imatinib (trade name Gleevec) in cases of chronic myeloid leukemia. Cancer cells often become resistant to a given drug, so researchers continue searching for new drugs that target proteins that contribute to the cancerous phenotype. One recent promising approach uses drugs that lead to ubiquitination and proteasomal degradation of the target protein. Which of the following mutated proteins are good candidates for this approach? Choose one or more: A.proteins with loss-of-function mutations B.tumor suppressor genes C.proteins with gain-of-function mutations D.oncogenes
C and D
Abnormally stretchy skin is part of a genetic syndrome that could result from which of the following? A. synthesis of excess cellulose B. overactivity of proteinase that cleaves procollagen C. increased production of collagen D. loss of proteinase that cleaves procollagen E. hypersecretion of procollagen
D
All members of the nuclear receptor family A. are cell-surface receptors. B. do not undergo conformational changes. C. are found only in the cytoplasm. D. interact with signal molecules that diffuse through the plasma membrane.
D
Antibiotics should inhibit bacterial cell growth without generating side effects in the human patient, but that is not always the case. Some antibiotics that inhibit bacterial protein synthesis by binding to bacterial ribosomes induce negative side effects in patients. What is the most likely cause of these side effects? A. The antibiotics interfere with cytoplasmic ribosomes. B. The antibiotics interfere with ribosomes attached to the ER, impairing RER function. C. The antibiotics interfere with chloroplast ribosomes. D. The antibiotics interfere with mitochondrial ribosomes.
D
Based on your understanding of DNA replication, which statement best describes the daughter helices in a eukaryotic cell after one round of replication has taken place in the absence of telomerase? A. One daughter helix will have a gap at one end, while the other daughter helix will be normal. B. Both daughter helices will have gaps at both ends. C. One daughter helix will have gaps at both ends, while the other daughter helix will be normal. D. Both daughter helices will have a gap at only one end. E. A repair polymerase will replace all missing DNA, so both daughter helices will be the same size as the parent helix.
D
Epithelial cells line body cavities and, in organs like the intestine, separate the extracellular environment (intestinal lumen) from the body. The barrier function of epithelial tissues is important for maintaining homeostasis and preventing infections from gut-associated microbiota and viruses. Some bacteria and viruses compromise this barrier function, aiding their pathogenesis. Which of the following structures, most critical to the barrier function of epithelial tissue, is targeted by these infectious agents? A. hemidesmosomes B. gap junctions C. desmosomes D. tight junctions
D
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
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
In a DNA double helix, which strand serves as the template during replication? A. the strand that encodes a protein B. the strand that is richer in A and T nucleotides C. the strand that runs in the 3'-to-5' direction D. Both strands serve as templates during replication.E. the strand that runs in the 5'-to-3' direction
D
In bacteria, how does the cell recognize which strand is the newly synthesized strand and thus contains the mismatch? A. The newly synthesized strand is methylated. B. The sequences on both strands are cut. C. The sequence on the newly synthesized strand is made of RNA. D. The newly synthesized strand is unmethylated.
D
In desmosomes, cadherin molecules are anchored inside an epithelial cell to which type of cytoskeletal filament? A. microtubules B. actin filaments C. fibronectins D. intermediate filaments
D
In which phase of the cell cycle do cells check to determine whether the DNA is fully and correctly replicated? A. at the transition between G1 and S B. when cells enter G0 C. during M D. at the end of G2
D
Intermediate filaments are found in what structure? A. cell cortex B. centrosomes C. cilia D. nuclear lamina E. mitotic spindle
D
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.
D
Mutations that prevent Bcl2 family proteins Bax and Bak from interacting with the outer mitochondrial membrane would have which effect? A. triggering the release of cytochrome c and promoting apoptosis B. preventing the release of cytochrome c and triggering the activation of procaspase-9 C. triggering the release of cytochrome c and promoting the assembly of the apoptosome D. preventing the release of cytochrome c and inhibiting apoptosis E. preventing the release of cytochrome c and promoting the assembly of the apoptosome
D
Ras is activated by a Ras-activating protein that does what? A. causes Ras to hydrolyze its bound GTP B. phosphorylates Ras C. causes Ras to interact with a phosphorylated RTK D. causes Ras to exchange GDP for GTP E. dephosphorylates Ras
D
Sickle-cell anemia is an example of an inherited disease. Individuals with this disorder have misshapen (sickle-shaped) red blood cells caused by a change in the sequence of the β-globin gene. What is the nature of the change? A. chromosome loss B. base-pair insertion C. gene duplication D. base-pair change
D
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
The length of time a G protein will signal is determined by the A. activity of phosphatases that turn off G proteins by dephosphorylating Gα. B. activity of phosphatases that turn GTP into GDP. C. degradation of the G protein after Gα separates from Gβγ. D. GTPase activity of Gα.
D
The loss of purine bases from a strand of DNA is typically caused by which of the following? A. deamination B. ultraviolet radiation C. replication error D. a spontaneous chemical reaction E. double-strand DNA break
D
The nucleotide sequence of one DNA strand in a DNA double helix is 5'-CATTGCCAGAAAAAT-3'. What is the sequence of the complementary strand produced during replication? A. 5'-GTAACGGTCTTTTTA-3' B. 5'-TAAAAAGACCGTTAC-3' C. 5'-CATTGCCAGAAAAAT-3' D. 5'-ATTTTTCTGGCAATG-3' E. 5'-GATTCGGAGTTTTTA-3'
D
The principal microtubule-organizing center in animal cells is the A. centromere. B. kinetochore. C. cell cortex D. centrosome.
D
When the hormone insulin is released into the bloodstream, what form of cell-cell signaling is being used? A. neuronal B. contact-dependent C. paracrine D. endocrine
D
Which is true of cadherin proteins? A. They allow ions and small molecules to pass from one plant cell to another. B. They create an electrical and metabolic coupling between epithelial cells. C. They anchor epithelial cells to the basal lamina. D. They link epithelial cells together by binding to similar cadherins in adjacent epithelial cells.
D
Which of the following is not a key behavior of cancer cells? A. They are less prone than normal cells to kill themselves by apoptosis. B. Most are genetically unstable, with a greatly increased mutation rate. C. They can often proliferate indefinitely. D. They consume neighboring cells to fuel their excessive proliferation. E. They are abnormally invasive.
D
Which of the following statements about apoptosis is TRUE? A. Cells that constitutively express Bcl2 will be more prone to undergo apoptosis. B. The prodomain of procaspases contains the catalytic activity necessary for procaspase activation. C. Bax and Bak promote apoptosis by binding to procaspases in the apoptosome. D. Apoptosis can be promoted by the release of cytochrome c into the cytosol from mitochondria.
D
Which type of mutation would not typically convert a proto-oncogene into an oncogene? A. gene amplification B. chromosomal rearrangement that leads to overproduction of the normal proto-oncogene protein C. chromosomal rearrangement that leads to the production of a hyperactive protein D. chromosomal deletion of the region containing the proto-oncogene E. mutation in the coding sequence that leads to the production of a hyperactive protein
D
What is the difference between a malignant and benign tumor? A. A malignant tumor proliferates in defiance of normal constraints, while a benign tumor does not. B. A benign tumor can be treated, while a malignant tumor cannot. C. A malignant tumor grows into a large destructive mass, whereas a benign tumor remains very small. D. A benign tumor grows from a single cell, whereas a malignant tumor arises from multiple cells, making it more difficult to eradicate. E. A malignant tumor invades and colonizes other tissues, while a benign tumor does not.
E
When a muscle is stimulated to contract, myosin heads walk along actin filaments in repeated cycles of attachment and detachment. Which of the following represents a correct description of the events in this cycle? A. ATP binding enhances the affinity of myosin for actin; myosin attaches to actin; the power stroke puts myosin in a "rigor" configuration; myosin is "cocked" as its head is displaced along the actin filament. B. ATP hydrolysis enhances the affinity of myosin for actin; myosin is "cocked" as its head is displaced along the actin filament; myosin attaches to actin; the power stroke puts myosin in a "rigor" configuration. C. ATP binding enhances the affinity of myosin for actin; myosin attaches to actin; myosin is "cocked" as its head is displaced along the actin filament; the power stroke puts myosin in a "rigor" configuration. D. The power stroke puts myosin in a "rigor" configuration; myosin attaches to actin; myosin is "cocked" as its head is displaced along the actin filament; ATP hydrolysis enhances the affinity of myosin for actin. E. Myosin attaches to actin; ATP binding reduces the affinity of myosin for actin; myosin is "cocked" as its head is displaced along the actin filament; the power stroke puts myosin in a "rigor" configuration.
E
True or False: Homologous recombination occurs only in eukaryotes.
False
