Cell Bio Chapter 18 Quiz
Which one 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 is promoted by the release of cytochrome c into the cytosol from mitochondria.
Apoptosis is promoted by the release of cytochrome c into the cytosol from mitochondria.
You create cells with a version of Cdc6 that cannot be phosphorylated and thus cannot be degraded. Which of the following statements describes the likely consequence of this change in Cdc6? a) Cells will enter S phase prematurely. b) Cells will be unable to complete DNA synthesis. c) The origin recognition complex (ORC) will be unable to bind to DNA. d) Cdc6 will be produced inappropriately during M phase.
Cells will be unable to complete DNA synthesis.
Which of the following statements is true? a) Before DNA replication begins, chromosomes consist of two sister chromatids that are bound tightly together. b) Cohesins hold sister chromatids together. c) Condensins hold sister chromatids together.
Cohesins hold sister chromatids together.
MPF activity was discovered when cytoplasm from a Xenopus M-phase cell was injected into Xenopus oocytes, inducing the oocytes to form a mitotic spindle. In a control experiment, Xenopus interphase cytoplasm was injected into oocytes and shown not to induce the formation of a mitotic spindle. Which of the following statements is not a legitimate conclusion from the control experiment? a) The piercing of the oocyte membrane by a needle is insufficient to cause mitotic spindle formation. b) An increased volume of cytoplasm is insufficient to cause mitotic spindle formation. c) Injection of extra RNA molecules is insufficient to cause mitotic spindle formation. d) Components of an interphase nucleus are insufficient to cause mitotic spindle formation.
Components of an interphase nucleus are insufficient to cause mitotic spindle formation.
Which of the following statements is false? a) Cyclins vary in concentration at different stages of the cycle. b) Cyclins help activate Cdks by phosphorylating them. c) Cyclins help guide Cdks to the proteins the CDK phosphorylate. d) Cyclins are degraded at specific times in the cycle. e) Cyclins have no enzymatic activity on their own.
Cyclins help activate Cdks by phosphorylating them.
Which of the following processes occur only in S phase of the cell cycle? a) Organelle replication b) Cell growth c) Chromosome segregation d) DNA replication
DNA replication
The inactivation of M-Cdk leads to which of the following? a) Onset of mitosis b) Onset of G2 phase c) Exit from S phase d) Exit from mitosis
Exit from mitosis
Which organelle fragments during mitosis? a) endoplasmic reticulum b) Golgi apparatus c) mitochondrion d) chloroplast
Golgi apparatus
Which one of the following statements is true? a) Anaphase A must be completed before anaphase B can take place. b) In cells in which anaphase B predominates, the spindle will elongate much less than in cells in which anaphase A dominates. c) In anaphase A, both kinetochore and interpolar microtubules shorten. d) In anaphase B, microtubules associated with the cell cortex shorten.
In anaphase B, microtubules associated with the cell cortex shorten.
Which of the following statements about the anaphase-promoting complex (APC) is false? a) It promotes the degradation of proteins that regulate M phase. b) It inhibits M-Cdk activity. c) It is continuously active throughout the cell cycle. d) M-Cdk stimulates its activity.
It is continuously active throughout the cell cycle.
Which of the following statements about kinetochores is true? a) Kinetochores assemble onto chromosomes during late prophase. b) Kinetochores contain DNA-binding proteins that recognize sequences at the telomere of the chromosome. c) Kinetochore proteins bind to the tubulin molecules at the minus end of microtubules. d) Kinetochores assemble on chromosomes that lack centromeres.
Kinetochores assemble onto chromosomes during late prophase.
Which of the following statements is false? Checkpoints of cell-cycle control system ensure that: a) the environment is favorable for the cell to initiate DNA replication. b) M phase is completed before cytokinesis begins. c) all chromosomes are attached to the mitotic spindle before the chromosomes are segregated to the two daughter cells. d) all DNA is replicated before M phase begins.
M phase is completed before cytokinesis begins.
Which of the following statements is true? a) Many cells die by necrosis during normal animal development. b) Many cells die by necrosis in many normal, adult, human tissues. c) Many cells die by apoptosis in many normal, adult, human tissues.
Many cells die by apoptosis in many normal, adult, human tissues.
Which of the following statements about the cell cycle is false? a) Once a cell decides to enter the cell cycle, the time from start to finish is the same in all eucaryotic cells. b) An unfavorable environment can cause cells to arrest in G1. c) A cell has more DNA during G2 than it did in G1. d) The cleavage divisions that occur in an early embryo have short G1 and G2 phases.
Once a cell decides to enter the cell cycle, the time from start to finish is the same in all eucaryotic cells.
The five stages of mitosis occur in which order? a) Anaphase, prometaphase, metaphase, telophase, prophase b) Prophase, metaphase, prometaphase, telophase, anaphase c) Telophase, anaphase, prophase, prometaphase, metaphase d) Prophase, prometaphase, metaphase, anaphase, telophase e) Anaphase, telophase, prometaphase, metaphase, prophase
Prophase, prometaphase, metaphase, anaphase, telophase
In the cell cycle, duplication of the centrosome begins in: a) G1 phase b) M phase c) prophase d) S phase e) G2 phase
S phase
Which of the following statements is false? a) Mitotic Cdk must be phosphorylated by an activating kinase (Cak) before it is active b) Phosphorylation of mitotic Cdk by the inhibitory kinase (Wee1) makes the Cdk inactive, even if it is phosphorylated by the activating kinase. c) Active M-Cdk phosphorylates the activating phosphatase (Cdc25) in a positive feedback loop d) The activating phosphatase (Cdc25) removes all phosphates from mitotic Cdk so that M-Cdk will be active.
The activating phosphatase (Cdc25) removes all phosphates from mitotic Cdk so that M-Cdk will be active.
Which of the following statements is false? a) The activation of S-Cdk initiates DNA replication. b) The activation of S-Cdk helps prevent the onset of M phase. c) DNA replication occurs only in S phase. d) The activation of S-Cdk helps prevent DNA replication occurring more than once each cycle.
The activation of S-Cdk helps prevent the onset of M phase.
Which of the following descriptions is consistent with the behavior of a cell that lacks a protein required for a checkpoint mechanism that operates in G2? a) The cell would be unable to enter M phase. b) The cell would be unable to enter G2. c) The cell would enter M phase under conditions when normal cells would not. d) The cell would pass through M phase more slowly than normal cells.
The cell would enter M phase under conditions when normal cells would not.
What would be the most obvious outcome of repeated cell cycles consisting of S phase and M phase only? a) Cells would not be able to replicate their DNA. b) he mitotic spindle could not assemble c) Cells would get larger and larger. d) The cells produced would get smaller and smaller.
The cells produced would get smaller and smaller.
Which of the following is the first obvious visible sign that a cell is about to enter M phase? a) The chromosomes replicate. b) The centrosome replicates. c) The chromosomes condense. d) The nuclear membrane breaks down.
The chromosomes condense.
Which one of the following statements is false? a) The cleavage furrow is a puckering of the plasma membrane caused by the constriction of a ring of filaments attached to the plasma membrane. b) The cleavage furrow will not begin to form in the absence of a mitotic spindle. c) The cleavage furrow always forms perpendicular to the interpolar microtubules. d) The cleavage furrow always forms in the middle of the cell.
The cleavage furrow always forms in the middle of the cell.
Which of the following statements are is false? a) Some Bcl2 family members promote apoptosis, whereas others inhibit apoptosis. b) The death-promoting members of the Bcl2 family include Bcl2 itself. c) Bax and Bak are death-promoting members of the Bcl2 family that induce the release of cytochrome c from mitochondria into the cytosol. d) Some death-inhibiting members of the Bcl2 family inhibit apoptosis by blocking cytochrome c release from mitochondria.
The death-promoting members of the Bcl2 family include Bcl2 itself.
Which of the following statements is false? a) DNA synthesis begins at origins of replication b) The loading of the origin recognition complexes (ORCs) is triggered by S-Cdk. c) The phosphorylation and degradation of Cdc6 help to ensure that DNA is replicated only once in each cell cycle. d) DNA synthesis can only begin after pre-replicative complexes assembles on the ORCs.
The loading of the origin recognition complexes (ORCs) is triggered by S-Cdk.
Which of the following statements is true? a) The mitotic spindle is largely made of intermediate filaments. b) The contractile ring is made largely of microtubules and actin filaments. c) The contractile ring divides the nucleus in two. d) The mitotic spindle helps segregate the chromosomes to the two daughter cells.
The mitotic spindle helps segregate the chromosomes to the two daughter cells.
Which of the following events does not usually occur during interphase? a) Cells grow in size. b) The nuclear envelope breaks down. c) DNA is replicated. d) The centrosomes are duplicated.
The nuclear envelope breaks down.
Which of the following statements is false? a) The microtubules bound to a mitotic chromosome must attach to opposite poles of the spindle for the daughter chromosomes to be segregated properly. b) The pairing of homologous chromosomes during prometaphase is called bi-orientation. c) Attachment of mitotic chromosomes to both poles of the spindle creates tension, which signals the chromosomes are ready to be separated. d) The cell cycle control system monitors the tension on the kinetochores to ensure correct chromosome attachment.
The pairing of homologous chromosomes during prometaphase is called bi-orientation.
Which of the following statements describes how mitogens operate? a) They suppress apoptosis. b) They overcome the intracellular braking mechanisms that tend to block progression through the cell cycle. c) they directly phosphoryalte and activate Cdks
They overcome the intracellular braking mechanisms that tend to block progression through the cell cycle.
Which of the following statements describe how growth factors stimulate animal cell enlargement? a) They stimulate microtubule polymerization. b) They stimulate an influx of extracellular water into the cytosol. c) They stimulate intracellular protein synthesis. d) They stimulate DNA replication.
They stimulate intracellular protein synthesis.
Which of the following is not good direct evidence that the cell-cycle control system is conserved through billions of years of divergent evolution? a) A yeast cell lacking Cdk function can use the human Cdk to substitute for its missing Cdk during the cell cycle. b) The amino acid sequences of cyclins in plants are similar to the amino acid sequences of cylins in humans. c) The Cdk proteins in humans share conserved phosphorylation sites with the Cdk proteins in yeast. d) Yeast cells have only one Cdk, whereas humans have many Cdks.
Yeast cells have only one Cdk, whereas humans have many Cdks.
Of the following mutations, which are likely to cause cell-cycle arrest? a) a mutation in a gene encoding a cell-surface mitogen receptor that makes the receptor active even in the absence of the mitogen b) a mutation that allowed G1-Cdk to be active independently of its phosphorylation status c) a mutation that removed the phosphorylation sites on the Rb protein d) a mutation that inhibited the activity of Rb
a mutation that removed the phosphorylation sites on the Rb protein
the contractile ring is made of a) microtubules b) actin and myosin c) condensins d) cohesins e) integrins
actin and myosin
The activation of M-Cdk requires: a) the binding of M cyclin. b) the phosphorylation of the Cdk. c) the dephosphorylation of the Cdk. d) all of the above
all of the above
The size of a human organ often depends on: A. the death of cells during its development. B. the proliferation of cells during its development. C. the size of its cells. D. All of the above
all of the above
When introduced into mitotic cells, which of the following is expected to impair anaphase B but not anaphase A? a) an antibody against myosin b) ATPγS, a nonhydrolyzable ATP analog that binds to and inhibits ATPases c) an antibody against the motor proteins that move from the plus end of microtubules to the minus end d) an antibody against the motor proteins that move from the minus end of microtubules toward the plus end
an antibody against the motor proteins that move from the minus end of microtubules toward the plus end
The spindle assembly checkpoint, which blocks the initiation of anaphase until all chromosomes are properly attached to the mitotic spindle, depends on: a) cohesin degradation b) M-cyclin degradation c) an inhibitory signal produced by inappropriately attached chromosomes d) a stimulatory signal produced by appropriately attached chromosomes
an inhibitory signal produced by inappropriately attached chromosomes
Condensins ________________. a) are degraded when cells enter M-phase b) assemble into complexes on the DNA when phosphorylated by M-Cdk c) are involved in holding sister chromatids together d) bind to DNA before DNA replication begins
assemble into complexes on the DNA when phosphorylated by M-Cdk
Which of the following precede the re-formation of the nuclear envelope during M phase in animal cells? a) assembly of the contractile ring b) decondensation of chromosomes c) reassembly of the nuclear lamina d) transcription of nuclear genes
assembly of the contractile ring
The loss of its cyclin causes a Cdk to: a) become active. b) be degraded in proteasomes. c) become inactive. d) phosphorylate its target proteins.
become inactive.
For a Cdk to be active, it must: a) bind a cyclin. b) increase in concentration at a specific time in the cycle. c) dissociate from its bound cyclin. d) translocate from the cytoplasm to the nucleus.
bind a cyclin.
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
by means of an intracellular suicide program
The proteases that dismantle the cell during apoptosis are called: a) lysozymes b) condensins c) caspases d) carapases
caspases
Apoptosis differs from necrosis in that necrosis ________________. a) requires the reception of an extracellular signal b) causes DNA to fragment c) causes cells to swell and burst, whereas apoptotic cells shrink and condense d) involves a caspase cascade
causes cells to swell and burst, whereas apoptotic cells shrink and condense
If a cell is deprived of proliferation signals for long enough, it can enter a specialized state (G0), in which: a) cell division is suspended for an indefinite period of time. b) the cell division is permanently arrested. c) the cell stops growing d) the cell cannot survive for long
cell division is suspended for an indefinite period of time.
The principal microtubule organizing center in animal cells is the ____________. a) centrosome b) centromere c) kinetochore d) cell cortex
centrosome
At the end of DNA replication, the sister chromatids are held together by the ___________. a) kinetochores b) securins c) cohesins d) histones
cohesins
The shortening and thickening of chromosomes in M phase depends on: a) microtubules b) actin and myosin c) condensins d) cohesins e) all of the above
condensins
Levels of Cdk activity change during the cell cycle, in part, because ________________. a) the Cdks phosphorylate each other b) the Cdks activate the cyclins c) Cdk degradation precedes entry into the next phase of the cell cycle d) cyclin levels change during the cycle
cyclin levels change during the cycle
A cell with nuclear lamins that cannot be phosphorylated in M phase will be unable to ________________. a) reassemble its nuclear envelope at telophase b) disassemble its nuclear lamina at prometaphase c) begin to assemble a mitotic spindle d) condense its chromosomes at prophase
disassemble its nuclear lamina at prometaphase
Cells in the G0 state ________________. a) do not divide b) cannot re-enter the cell cycle c) have entered this arrest state from either G1 or G2 d) have duplicated their DNA
do not divide
The activation of M-Cdk begins abruptly mainly because: a) M cyclin increases abruptly. b) M cyclin is rapidly phosphorylated and thereby activated. c) the mitotic Cdk increases abruptly. d) each M-Cdk complex can activate more M-Cdk. e) all of the above
each M-Cdk complex can activate more M-Cdk.
Apoptosis is a form of programmed cell death, in which cells kill themselves by migrating to the blood stream where they are carried to the liver for destruction. a) true b) false
false
Different cyclins always bind to different Cdks. a) true b) false
false
During the cell cycle, cell growth occurs only in the gap phases, G1 and G2. a) true b) false
false
mitosis always produces daughter cells of equal size a) true b) false
false
the location of the nucleus determines the site of cleavage during cytokinesis? a) true b) false
false
Which of the following does not occur during M phase in animal cells? a) growth of the cell b) condensation of chromosomes c) breakdown of nuclear envelope d) attachment of chromosomes to microtubules
growth of the cell
A mutant yeast strain stops proliferating when shifted from 25°C to 37°C. When these cells are analyzed at the two different temperatures, using a machine that sorts cells according to the amount of DNA they contain, the following graphs are obtained. Which of the following would not explain the results with the mutant? a) inability to initiate DNA replication b) inability to begin M phase c) inability to activate proteins needed to enter S phase d) inappropriate production of a signal that causes the cells to remain in G1
inability to begin M phase
You have isolated a strain of mutant yeast cells that divides normally at 30°C but cannot enter M phase at 37°C. You have isolated its mitotic cyclin and mitotic Cdk and find that both proteins are produced and can form a normal M-Cdk complex at both temperatures. Which of the following temperature-sensitive mutations could not be responsible for the behavior of this strain of yeast? a) inactivation of a protein kinase that acts on the mitotic Cdk kinase b) inactivation of an enzyme that ubiquitylates M cyclin c) inactivation of a phosphatase that acts on the mitotic Cdk kinase d) a decrease in the levels of a transcriptional regulator required for producing sufficient amounts of M cyclin
inactivation of an enzyme that ubiquitylates M cyclin
The G1 DNA damage checkpoint ________________. a) causes cells to proceed through S phase more quickly b) involves the degradation of p53 c) is activated by errors caused during DNA replication d) involves the inhibition of cyclin-Cdk complexes by p21
involves the inhibition of cyclin-Cdk complexes by p21
Microtubules capture chromosomes by binding to: a) centromere regions of the sister chromatids. b) cohesins on the sister chromatids. c) condensins on the condensed chromosomes. d) kinetochores on the sister chromatids.
kinetochores on the sister chromatids.
chromosomes line up at the spindle equator during a) telophase b) metaphase c) prophase d) anaphase
metaphase
the mitotic spindle is made of a) actin b) microtubules c) condensins d) cohesins e) all of the above
microtubules
Disassembly of the nuclear envelope ________________. a) causes the inner nuclear membrane to separate from the outer nuclear membrane b) results in the conversion of the nuclear envelope into protein-free membrane vesicles c) is triggered by the phosphorylation of integrins d) must occur for kinetochore microtubules to form in animal cells
must occur for kinetochore microtubules to form in animal cells
When a cell is acutely injured, it usually dies by: a) apoptosis b) necrosis c) endocytosis d) phagocytosis
necrosis
The anaphase promoting complex (APC) triggers the onset of anaphase by: a) precipitating the destruction of the cohesens that hold the sister chromatids together. b) precipitating the destruction of the condensins that keep the replicated chromosomes in a condensed state. c) stimulating the spindle poles in move apart d) all of the above
precipitating the destruction of the cohesens that hold the sister chromatids together.
In the cell cycle, the mitotic spindle begins to assemble in: prometaphase b) prophase c) metaphase d) anaphase e) telophase
prophase
The nuclear envelope breaks down at the start of prometaphase because: a) the replicated chromosomes decondense. b) proteins that form the nuclear pores and nuclear lamina become phosphorylated. c) the sister chromatids separate. d) the growing mitotic spindle breaks the envelope down.
proteins that form the nuclear pores and nuclear lamina become phosphorylated.
Cytokinesis in animal cells ________________. a) requires ATP b) leaves a small circular 'scar' of actin filaments on the inner surface of the plasma membrane c) is often followed by phosphorylation of integrins in the plasma membrane d) is assisted by motor proteins that pull on microtubules attached to the cell cortex
requires ATP
At specific times in the cell cycle: a) some cyclins are phosphorylated and degraded in proteasomes. b) some Cdks are ubiquitylated and degraded in proteasomes. c) some cyclins are ubiquitylated are degraded in proteasomes. d) some Cdks are phosphorylated and degraded in proteasomes.
some cyclins are ubiquitylated are degraded in proteasomes.
In dividing plant cells, a new cell wall is formed between two sets of chromosomes via a structure called a phragmoplast, which is built by vesicles largely originating from which organelle? a) the endoplasmic reticulum b) the Golgi apparatus c) the vacuole d) the chloroplasts e) vesicles from the broken down nuclear envelope
the Golgi apparatus
which of the following organelles fragments during mitosis? a) mitochondria b) the Golgi apparatus c) the peroxisomes d) the lysozomes e) choroplasts
the Golgi apparatus
Cells without centrosomes can still assemble a functional bipolar mitotic spindle, because: a) nuclear pore complexes can nucleate microtubule assembly. b) microtubules can organize themselves into a bipolar spindle. c) the chromosomes themselves can nucleate microtubule assembly. d) motor proteins can nucleate microtubule assembly.
the chromosomes themselves can nucleate microtubule assembly.
The reassembly of the nuclear envelope at telophase depends on: a) the phosphorylation of nuclear lamins and nuclear of pore proteins. b) the dephosphorylation of both nuclear lamins and nuclear pore proteins. c) the dephosphorylation of M cyclin. d) the phosphorylation of M cyclin
the dephosphorylation of both nuclear lamins and nuclear pore proteins.
Different cyclin-dependent protein kinases (Cdks) trigger different stages of the cell cycle in part because: a) their concentrations increase at different stages of the cycle. b) their activities increase at different stages of the cycle. c) they are degraded at different stages of the cycle. d) All of the above
their activities increase at different stages of the cycle.
The cell-cycle control system uses Cdk inhibitory proteins: a) to stop one phase of the cycle and trigger another b) to degrade Cdks c) to degrade cyclins d) to arrest the cell cycle at specific chekcpoitns
to arrest the cell cycle at specific checkpoints.
Cancer cells fail to obey normal "social" controls on cell behavior and therefore outgrow, out-divide and out-survive their normal neighbors. a) true b) false
true
Cell growth, unlike cell proliferation, does not depend on the cell-cycle control system. a) true b) false
true
In response to DNA damage in a proliferating cell, the p53 protein can arrest the cell cycle or induce the cell to kill itself. a) true b) false
true
Is the following statement true or false? After the nuclear envelope breaks down, microtubules gain access to the chromosomes and, every so often, a randomly probing microtubule captures a chromosome and ultimately connects to the kinetochore to become a kinetochore microtubule of the spindle. a) true b) false
true
Many cells in normal animal tissues require extracellular signals from other cells to avoid apoptosis. This could be a mechanism for ensuring that cells only survive when and where they are needed. a) true b) false
true
Some cells such as nerve and muscle cells grow mainly after they have withdrawn from the cell cycle, indicating that the cell-cycle control system is not required for cell growth. a) true b) false
true
apoptosis depends on a tightly regulated proteolytic cascade a) true b) false
true
the cytoskeleton carries out both mitosis and cytokinesis a) true b) false
true
Which of the following processes does NOT help move the daughter chromosomes to opposite poles of the spindle in anaphase? a) Kinetochore microtubules shorten by depolymerization. b) The spindle poles move apart. c) Actin and myosin filaments in the spindle contract. d) Microtubule motor proteins hydrolyse ATP at the kinetochores.
Actin and myosin filaments in the spindle contract.
Which of the following statements is false? a) Activated M-Cdk triggers the onset of cytokinesis. b) Activated S-Cdk initiates DNA replication. c) G1-Cdks and G1/S-Cdks help drive cells through G1 into S phase.
Activated M-Cdk triggers the onset of cytokinesis.
Which one of the following statements regarding mitosis is true? a) Sister chromatids are held together by condensins from the time they arise by DNA replication until the time they separate at anaphase. b) Cohesins are required to make the chromosomes more compact and thus to prevent tangling between different chromosomes. c) The mitotic spindle is composed of actin filaments and myosin filaments. d) Microtubule-dependent motor proteins and microtubule polymerization and depolymerization are mainly responsible for the organized movements of chromosomes during mitosis. e) The centromere nucleates a radial array of microtubules called an aster, and its duplication is triggered by S-Cdk.
Microtubule-dependent motor proteins and microtubule polymerization and depolymerization are mainly responsible for the organized movements of chromosomes during mitosis.
Which two processes together constitute the M phase of the cell cycle? a) Interphase and mitosis b) Mitosis and cytokinesis c) Interphase and metaphase d) S phase and G1
Mitosis and cytokinesis
Which of the following statements is false? a) Cytokinesis in plant cells is mediated by the microtubule cytoskeleton. b) Small membrane vesicles derived from the Golgi apparatus deliver new cell wall material for the new wall of the dividing cell. c) The phragmoplast forms from the remains of interpolar microtubules of the mitotic spindle. d) Motor proteins walking along the cytoskeleton are important for the contractile ring that guides formation of the new cell wall.
Motor proteins walking along the cytoskeleton are important for the contractile ring that guides formation of the new cell wall.
which of the following statements is true? a) The mitotic spindle is made primarily of microtubules and actin filaments. b) New microtubules grow out in random directions from the centrosomes. c) The dynamic instability of microtubules decreases at the start of mitosis. d) The minus end of a microtubule has a net negative charge, whereas the positive end has a net positive charge.
New microtubules grow out in random directions from the centrosomes.
