Chapter 18 The Cell Division Cycle
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.
Apoptosis can be promoted by the release of cytochrome c into the cytosol from mitochondria.
Of the following mutations, which are likely to cause cell-cycle arrest? If you predict a cell-cycle arrest, indicate whether the cell will arrest in early G1, late G1, or G2. Explain your answers. 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 destroyed the kinase activity of S-Cdk C.a mutation that allowed G1-Cdk to be active independently of its phosphorylation status D.a mutation that removed the phosphorylation sites on the Rb protein E.a mutation that inhibited the activity of Rb
B and D are likely to cause cell-cycle arrest. A.Because ligand-independent activation of a mitogen receptor will probably make the cell divide when it otherwise might not, this mutation is unlikely to cause a cell-cycle arrest. B.This mutation is likely to cause cell-cycle arrest in late G1. Without S-Cdk activity, the cells will probably be unable to enter S phase. C.Phosphorylation-independent activity of G1-Cdk is unlikely to lead to cell-cycle arrest; the cells should progress through the cycle, although the kinetics and fine regulation of the cycle may be altered. D.This mutation is likely to cause cell-cycle arrest in early G1. Unphosphorylated Rb will inhibit the transcription of genes required for progression through G1 and into S phase. This inhibition is normally released on phosphorylation of Rb. If Rb cannot be phosphorylated, it will always inhibit transcription of these genes, leading to arrest in early G1. E.If Rb is inactivated by a mutation, cells will be more likely to divide in the absence of extracellular mitogens, which is the opposite of a cell-cycle arrest.
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 organelle fragments during mitosis? a.endoplasmic reticulum b.Golgi apparatus c.mitochondrion d.chloroplast
Golgi apparatus
Which 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? 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 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 eukaryotic 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 eukaryotic cells.
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; each word or phrase should be used only once. APCG2 phasemetaphase Cdksinterphasemicrotubules condensationintraphasemitosis cytokinesiskinesinsmyosins meiosisM phaseS phase G1 phaseM-CdkS-Cdk G1-Cdk The cell cycle consists of an alternation between __________, which appears as a period of dramatic activity under the microscope, and a preparative period called __________, which consists of three phases called __________, __________, and __________. During M phase, the nucleus divides in a process called __________, and the cytoplasm splits in two in a process called __________. The cell-cycle control system relies an increase in the activity of __________ to trigger DNA replication. Inactivation of __________ is required to exit from M phase after chromosome segregation.
The cell cycle consists of an alternation between M phase, which appears as a period of dramatic activity under the microscope, and a preparative period called interphase, which consists of three phases called G1 phase, S phase, and G2 phase. During M phase, the nucleus divides in a process called mitosis, and the cytoplasm splits in two in a process called cytokinesis. The cell-cycle control system relies on an increase in the activity of S-Cdk to trigger DNA replication. Inactivation of M-Cdk is required to exit from M phase after chromosome segregation.
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.The cells would not be able to replicate their DNA. b.The mitotic spindle could not assemble. c.The 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 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 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 prereplicative complexes assemble 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.
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; each word or phrase should be used only once. anaphasedifferentiationmyostatin annihilationG0nourishment arrestaseG1nutrition Bcl2G2phosphatases biosyntheticgrowth factorsproliferation cyclininterphasereceptor cascadesligandS caspaseMsurvival factors Cdkmitogenstranscription The survival, __________, and size of each cell in an animal are controlled by extracellular signal molecules secreted by neighboring and distant cells. Many of these signal molecules bind to a cell-surface __________ and trigger various intracellular signaling pathways. One class of signal molecules, called __________, stimulates cell division by releasing the molecular brakes that keep cells in the __________or __________ phase of the cell cycle. Members of a second class of signal molecules are called __________, because they stimulate cell growth and an increase in cell mass. The third class of signal molecules, called __________, inhibits apoptosis by regulating members of the __________ family of proteins. In addition to such stimulatory factors, some signal proteins, such as __________ act negatively on other cells, inhibiting their survival, growth, or proliferation.
The survival, proliferation, and size of each cell in an animal are controlled by extracellular signal molecules secreted by neighboring and distant cells. Many of these signal molecules bind to a cell-surface receptor and trigger various intracellular signaling pathways. One class of signal molecules, called mitogens, stimulates cell division by releasing the molecular brakes that keep cells in the G0 or G1 phase of the cell cycle. Members of a second class of signal molecules are called growth factors, because they stimulate cell growth and an increase in cell mass. The third class of signal molecules, called survival factors, inhibits apoptosis by regulating members of the Bcl2 family of proteins. In addition to such stimulatory factors, some signal proteins, such as myostatin act negatively on other cells, inhibiting their survival, growth, or proliferation.
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 a 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 cyclins 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.
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
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.
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.
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
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 activity change during the cycle.
cyclin activity 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
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 reenter the cell cycle. c.have entered this arrest state from either G1 or G2. d.have duplicated their DNA.
do not divide.
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.
falls toward the end of M phase as a result of ubiquitylation and degradation.
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
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
Sister chromatid separation occurs because __________ are destroyed by the APC/C. a.securins b.cohesins c.kinetochores d.condensins
securins
A friend declares that chromosomes are held at the metaphase plate by microtubules that push on each chromosome from opposite sides. Which of the following observations does not support your belief that the microtubules are pulling on the chromosomes? a.the jiggling movement of chromosomes at the metaphase plate b.the way in which chromosomes behave when the attachment between sister chromatids is severed c.the way in which chromosomes behave when the attachment to one kinetochore is severed d.the shape of chromosomes as they move toward the spindle poles at anaphase
the jiggling movement of chromosomes at the metaphase plate