chapter 18

Which of the following statements is FALSE? A) Cdc25 dephosphorylation of Wee1 activates the kinase, promoting the G2/M transition B) phosphorylation of mitotic Cdk by the inhibitory kinase (Wee1) makes the Cdk inactive C) inhibiting the Cdc25 phosphatase will delay the G2/M transition D) the activating phosphatase (Cdc25) removes the phosphates from the mitotic Cdk that were added by Wee1, so that M-Cdk will be active

A) Cdc25 dephosphorylation of Wee1 activates the kinase, promoting the G2/M transition

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

A) do not divide

Mitogens are: A) extracellular signals that stimulate cell division B) transcription factors important for cyclin production C) kinases that cause cells to grow in size D) produced by mitotic cells to keep nearby neighboring cells from dividing

A) extracellular signals that stimulate cell division

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 in 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 and it did in G1 D) the cleavage divisions that occur in an early embryo have short G1 and G2 phases

A) once a cells decides of enter the cell cycle, the time from start to finish is the same in all eukaryotic cells

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

A) the growth of a cell

How does S-Cdk help guarantee the replication occurs only once during each cell cycle? A) it blocks the rise of Cdc6 concentration early in G1 B) it phosphorylates and inactivates DNA helicase C) it phosphorylates and inactivates Cdc6 D) it promotes the assembly of a per-replicative complex

C) it phosphorylates the assembly of a pre-replicative complex

You have isolated a strain of mutant yeast cells 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 protein kinase that acts of 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

B) inactivation of an enzyme that ubiquitylates M cyclin

Progression through the cell cycle requires a cyclin to bind to a Cdk because: A) the cyclins are the molecules with the enzymatic activity in the complex B) the binding of a cyclin to Cdk is required for Cdk enzymatic activity C) cyclin binding inhibits Cdk activity until the appropriate time in the cell cycle D) without cyclin binding, a cell-cycle checkpoint will be activated

B) the binding of a cyclin to Cdk is required for Cdk enzymatic activity

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 assemble on the ORCs

B) the loading of the origin recognition complexes (ORCs) is triggered by S-Cdk

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

B) the nuclear envelope breaks down

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 conditions when normal cells would not D) the cell would pass through M phase more slowly than normal cells

C) the cell would enter M phase conditions when normal cells would not

You engineer yeast cells that express the M cyclin during the S phase by replacing the gene regulatory sequences of the M cyclin gene with those of the S cyclin gene. Keeping mind that yeast cells have one common Cdk that binds to all cyclins, which of the following outcomes is LEAST likely during this experiment? A) there will be both M cyclin-Cdk and S cyclin-Cdk complexes in the cell during S phase B) some substrates that normally phosphorylated in M phase will now be phosphorylated in S phase C) G1 cyclin-Cdks will be activated earlier in G1 D) S-Cdk targets will be phosphorylated during S phase

C) G1 cyclin-Cdks will be activated earlier in G1

A cell that is terminally differentiated will: A) replicate its DNA B) reenter the cell cycle only once a year C) dismantle the cell-cycle control system D) arrest after S phase

C) dismantle the cell-cycle control system

The concentration of mitotic cyclin (M cyclin): A) rises markedly during the M phase B) is activated by phosphorylation C) falls towards the end of M phase as a result of ubiquitylation and degradation D) is the highest in G1 phase

C) falls toward the end of M phase as a result of ubiquitylation and degradation

The retinoblastoma (Rb) protein blocks cells from entering the cell cycle by A) phosphorylating Cdk B) marking cyclins for destruction by proteolysis C) inhibiting cyclin transcription D) activating apoptosis

C) inhibiting cycling transcription

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 the cells enter G0 C) during M D) at the end of G2

D) at the end of G2

MPF activity was discovered when cytoplasm from 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 for 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

D) components of an interphase nucleus are insufficient to cause mitotic spindle formation

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 cell cycle

D) cyclin activity change during the cell cycle

The G1 DNA damage checkpoint: A) causes cells to proceed through S phase more quickly B) involves the degredation of p53 C) is activated by errors caused during DNA replication D) involves the inhibition of cyclin-Cdk complexes by p21

D) involves the inhibition of cyclin-Cdk complexes by p21

What would be the most obvious outcome of repeated cell cycles consisting of S 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 would get smaller and smaller

D) the cells would get smaller and smaller

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

D) yeast cells have only one Cdk, whereas humans have many Cdks

True/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.

True

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.

a. Kinetochores assemble onto chromosomes during late prophase

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

a. 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.

a. by means of an intracellular suicide program.

The principal microtubule-organizing center in animal cells is the a. centrosome. b. centromere. c. kinetochore. d. cell cortex.

a. centrosome.

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.

a. requires ATP.

Sister chromatid separation occurs because _______________ are destroyed by the APC/C. a. securins b. cohesins c. kinetochores d. condensins

a. 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

a. the jiggling movement of chromosomes at the metaphase plate

You create cells with a version of the origin recognition complex, ORC, that cannot be phosphorylated by S-Cdk and thus cannot be inactivated. Which of the following statements describes the likely consequence of this change in ORC? a. Cells will enter S phase prematurely. b. Cells will replicate some regions of the genome more than once in a cell cycle. c. ORC will be unable to bind to DNA. d. DNA helicases will not be able to open up the double helix at the replication origin.

b. Cells will replicate some regions of the genome more than once in a cell cycle.

Which organelle fragments during mitosis? a. endoplasmic reticulum b. Golgi apparatus c. mitochondrion d. chloroplast

b. Golgi apparatus

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.

b. assemble into complexes on the DNA when phosphorylated by M-Cdk.

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.

b. disassemble its nuclear lamina at prometaphase.

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.

c. It is continuously active throughout the cell cycle.

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.

c. causes cells to swell and burst, whereas apoptotic cells shrink and condense.

At the end of DNA replication, the sister chromatids are held together by the a. kinetochores. b. securins. c. cohesins. d. histones.

c. cohesins.

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. Apoptosis can be promoted by the release of cytochrome c into the cytosol from mitochondria.

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.

d. In anaphase B, microtubules associated with the cell cortex shorten

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.

d. 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 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.

d. The cleavage furrow always forms in the middle of the cell.

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.

d. The mitotic spindle helps segregate the chromosomes to the two daughter cells.

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.

d. must occur for kinetochore microtubules to form in animal cells