Deck 18: Regulating the Eukaryotic Cell Cycle

Question 1

What are the biochemical activities of Wee1 and Cdc25 proteins? How do these activities regulate MPF?

Answer 1

Wee1 is a kinase that phosphorylates Cdc2 on Tyr-15 and inhibits its activity.Cdc25 is a phosphatase that removes this phosphate and re-establishes activity in the presence of a phosphate group on Thr-161 in Cdc2.

Question 2

Exit from mitosis depends upon the degradation of:

A)cohesion.
B)condensin.
C)cyclin B.
D)securin.

Answer 2

C

Question 3

Cyclin D/Cdk4 functions during:

A)G₁.
B)S.
C)G₂.
D)M.

Answer 3

A

Question 4

Injection of an immature Xenopus oocyte with MPF induces:

A)meiosis.
B)oocyte maturation.
C)synthesis of progesterone.
D)meiosis and oocyte maturation.

Question 5

Investigators found that the cyclin B concentration rises and falls in synchrony with mitotic events and MPF activity.However,correlation is not causality.How did they show that cyclin B was responsible for these cell-cycle events?

Question 6

Which of the following is a target of the APC?

A)Cdc25
B)cyclin B
C)separase
D)Cdc28

Question 7

During which stage of the cell cycle is the chromosome content of a mammalian liver cell 1n?

A)G₁
B)S
C)G₂
D none of the above

Question 8

Site-directed mutagenesis of Tyr-15 to Phe in cdc2:

A)results in the wee phenotype.
B)results in a phenotype similar to that caused by mutation in cdc25.
C)increases the possible number of phosphate groups on Cdc2.
D)prevents binding of Cdc13.

Question 9

Mitotic cyclin levels in early Xenopus embryos are regulated by:

A)phosphorylation.
B)synthesis and degradation of their mRNAs.
C)degradation by APC.
D)degradation by MPF.

Question 10

What is START? How does nutritional status determine whether S.cerevisiae cells will pass START?

Question 11

Human genes/proteins that regulate the cell cycle are most easily isolated by:

A)biochemical purification.
B)complementation of Xenopus mutants.
C)complementation of yeast mutants.
D)positional cloning.

Question 12

Which of the following S.pombe mutants is(are)larger than normal?

A)cdc2ᴰ
B)cdc25−
C)wee1−
D)cdc25− and wee1−

Question 13

During G₁,prereplication complexes:

A)are phosphorylated by B-type cyclin-CDKs.
B)are phosphorylated by DDK.
C)bind to ORC.
D)all of the above

Question 14

What is the difference between a kinetochore and a centromere?

Question 15

Which of the following is targeted by the SCF complex?

A)Cdh1
B)cyclin B
C)securin
D)Sic1

Question 16

Which of the following is a substrate of Cln3-Cdc28?

A)SBF
B)SPF
C)MPF
D)MBF

Question 17

All the following statements about destruction of cyclins are true,except:

A)Destruction is carried out by proteasomes.
B)Destruction is preceded by polyubiquitination.
C)Ubiquitination occurs at specific sites on target molecules.
D)Ubiquitin targets Cdks.

Question 18

What is a cdc mutant? What protein is encoded by cdc2 in fission yeast?

Question 19

The S.cerevisiae homolog of Xenopus MPF is:

A)Cdc13-Cdc2.
B)Cdc25-Cdc2.
C)Clb1-Cdc28.
D)Cln3-Cdc28.

Question 20

Name three activities of G₁ cyclin-CDKs that ensure progression through the cell cycle.

Question 21

Which of the following is NOT a way G1/S cyclin/cdks ensure progression through the cell cycle?

A)inactivate APC via Cdh1 phosphorylation
B)phosphorylate the S phase inhibitor (CKI)
C)activate SCF E3 ligase
D)activate expression of S-phase cyclins

Question 22

How does p53 function as a tumor-suppressor protein?

Question 23

Describe the experiment that demonstrated that phosphorylation of nuclear lamins is required for nuclear envelope breakdown during mitosis.

Question 24

How does the presence of unreplicated DNA prevent entry into mitosis?

Question 25

Which of the following inhibit(s)cyclin A/Cdk2 activity?

A)INK4
B)p21ᶜᴵᴾ
C)Rb
D)INK4 and Rb

Question 26

Breakdown of the nuclear envelope during mitosis is accomplished by CDK-dependent phosphorylation of lamins:

A)A and C,but not B.
B)A and B,but not C.
C)B and C but not A.
D)A,B,and C.

Question 27

What stimulus is required for quiescent cells to re-enter the cell cycle? What events occur after stimulation?

Question 28

Which of the following occurs during anaphase A?

A)The spindle elongates.
B)Kinetochores remain attached to shortening kinetochore microtubules.
C)Chromosomes move to the spindle equator.
D)The spindle poles move closer together.

Question 29

How do chromosome movements differ between meiosis I and meiosis II? Is spindle composition the basis for this distinction?

Question 30

Separase initiates sister chromatid segregation at anaphase by cleaving:

A)APC.
B)Cdc20.
C)cyclin B.
D)Scc1.

Question 31

Separation of spindle poles during spindle formation and anaphase B most likely depends on which of the following?

A)(+)end-directed microtubule motors at the cell cortex
B)(+)end-directed microtubule motors at the kinetochore
C)(−)end-directed microtubule motors in the microtubule overlap zone
D)(+)end-directed microtubule motors in the microtubule overlap zone

Question 32

DNA replication at each origin occurs only once during the cell cycle because of:

A)specificity of the origin-recognition complex (ORC).
B)S phase Cdk phosphorylating MCM helicase.
C)MCM helicase loading by M phase cyclins.
D)G1 cyclin/cdk activation of E2F.

Question 33

The stable attachment of sister kinetochores to microtubules emanating from opposite spindle poles is called:

A)merotelic attachment.
B)syntelic attachment.
C)amphitelic attachment.
D)monotelic attachment.

Question 34

Describe how Cdc14 triggers the exit from mitosis in the budding yeast,S.cerevisiae.

Question 35

After addition of serum to G₀-arrested mammalian cells,two classes of genes are expressed: early-response genes and delayed-response genes.Explain why expression of delayed-response genes is blocked by inhibitors of protein synthesis but expression of early-response genes is not.

Question 36

Centromeric Rec8 becomes cleaved during:

A)meiosis I.
B)meiosis II.
C)mitosis.
D)none of the above

Question 37

Failure of which cell-cycle checkpoint is most likely to result in nondysjunction?

A)chromosome-segregation checkpoint
B)DNA-damage checkpoint
C)unreplicated DNA checkpoint
D)dysreplicated DNA checkpoint

Question 38

During mitosis,the breakdown of the nuclear envelope depends on the:

A)disassembly following proteasomal degradation of intermediate filaments.
B)disassembly of lamin filaments following phosphorylation by mitotic cyclin/cdk complexes.
C)ubiquitination of mitotic cyclin proteins.
D)lamin filament dephosphorylation by cdc14.

Question 39

Chk1is activated by:

A)ATR.
B)Mad1.
C)p53.
D)Mad1 and p53.

Question 40

Compare cohesin function during mitosis and meiosis.

Question 41

You perform an experiment where you prevent Cdc20 from binding to APC
In a cell line that usually completes the cell cycle in 60 minutes.Your experiment prevents Cdc20 from binding to APC for 120 minutes,and then you fix and stain the DNA,securin,separase and cohesin proteins.Which of the following would NOT be found in the observed cell?

A)The cell would contain condensed chromosomes aligned at the metaphase plate.
B)Cohesins will be localized around the sister chromatids.
C)Securin would be bound to separase (appear to co-localize).
D)The DNA will be decondensed because the cell is in interphase.