Lodish Ch 19: Regulating the Eukaryotic Cell Cycle

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Questions and Answers

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

None of the above (correct)

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

Biochemical purification.

Positional cloning.

Complementation of Xenopus mutants.

Complementation of yeast mutants. (correct)

Injection of an immature Xenopus oocyte with MPF induces:

Meiosis and oocyte maturation. (correct)

Oocyte maturation.

Synthesis of progesterone.

Meiosis.

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

Ubiquitin targets Cdks. Signup and view all the answers

Mitotic cyclin levels in early Xenopus embryos are regulated by:

Degradation by APC. Signup and view all the answers

Which of the following is a target of the APC?

Cyclin B Signup and view all the answers

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

Results in the wee phenotype. Signup and view all the answers

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

cdc25 Signup and view all the answers

Exit from mitosis depends upon the degradation of:

Cyclin B. Signup and view all the answers

The S. cerevisiae homolog of Xenopus MPF is:

Clb1-Cdc28. Signup and view all the answers

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

SBF Signup and view all the answers

Which of the following is targeted by the SCF complex?

Sic1 Signup and view all the answers

During G1, prereplication complexes:

All of the above. Signup and view all the answers

Cyclin D/Cdk4 functions during:

G1 Signup and view all the answers

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

A, B, and C. Signup and view all the answers

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

Amphitelic attachment. Signup and view all the answers

Separase initiates sister chromatid segregation at anaphase by cleaving:

Scc1. Signup and view all the answers

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

p21 Signup and view all the answers

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

Chromosome-segregation checkpoint Signup and view all the answers

Chk1 is activated by:

ATR Signup and view all the answers

Centromeric Rec8 becomes cleaved during:

Meiosis II Signup and view all the answers

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

Disassembly of lamin filaments following phosphorylation by mitotic cyclin/cdk complexes. Signup and view all the answers

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

Activate SCF E3 ligase. Signup and view all the answers

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

S phase Cdk phosphorylating MCM helicase. Signup and view all the answers

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

(+) end-directed microtubule motors in the microtubule overlap zone Signup and view all the answers

Which of the following occurs during anaphase A?

Kinetochores remain attached to shortening kinetochore microtubules. Signup and view all the answers

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?

The DNA will be decondensed because the cell is in interphase. Signup and view all the answers

Study Notes

Regulating the Eukaryotic Cell Cycle

Cell Cycle Stage: A mammalian liver cell's chromosome content is 1n during the G₁ phase.
Kinetochore vs. Centromere: The kinetochore is a multiprotein complex at the centromeric region of sister chromatids. Microtubules attach to kinetochores. The centromere is part of the chromosome where sister chromatids join.
Human Gene Isolation: Complementation of yeast mutants is the easiest method to isolate human cell cycle-regulating genes/proteins.
Xenopus Oocyte Injection: Injecting immature Xenopus oocytes with MPF induces meiosis and oocyte maturation.
Cyclin Destruction: Cyclins are destroyed by proteasomes, preceded by polyubiquitination. This occurs at specific sites on the target molecules.
Mitotic Cyclin Regulation: Mitotic cyclin levels are regulated by synthesis, degradation of mRNAs, and degradation by the Anaphase-Promoting Complex (APC).
CDC Mutants: CDC mutants are organisms with temperature-sensitive mutations in genes required for cell cycle stages. At the nonpermissive temperatures, the mutants stop in the cell cycle at a specific point. The CDC2 gene in Schizosaccharomyces pombe encodes the cyclin-dependent kinase (CDK) protein.
APC Target: The protein cyclin B is a target of APC.
Weel and Cdc25: Weel is a kinase that phosphorylates Cdc2, inhibiting its activity. Cdc25 is a phosphatase that removes this phosphate, restoring activity (Cdc2).
Tyr-15 Mutation: Mutating Tyr-15 to Phe in cdc2 causes a phenotype similar to that of a mutation in cdc25.
S. pombe Mutants: cdc25 and wee1 mutants are larger than normal.
Mitotic Exit: Exit from mitosis depends on the degradation of cyclin B.
G₁ Cyclin-CDKs: Three activities of G₁ cyclin-CDKs include: inactivating APC, activating expression of S-phase cyclins, and phosphorylating S phase inhibitor for degradation.
Cyclin B Correlation: Investigators showed cyclin B is responsible for cell cycle events by treating Xenopus extracts with RNase, removing these events. Cyclin B mRNA restored the events.
Weel and Cdc25 Activities: Wee1 is a kinase that phosphorylates Cdc2, inhibiting its activity. Cdc25 is a phosphatase that removes the phosphate, restarting activity in Cdc2.
Xenopus MPF Homolog: Clb1-Cdc28 is the S. cerevisiae homolog of Xenopus MPF.
Cln3-Cdc28 Substrate: SBF is a substrate of Cln3-Cdc28.
SCF Complex Target: The SCF complex targets Sic1.
Prereplication Complexes in G₁: Prereplication complexes bind to ORC and are phosphorylated by B-type cyclin-CDKs and DDK.
Cyclin D/Cdk4 Function: Cyclin D/Cdk4 functions during the G₁ phase.
START in S. cerevisiae: START is a point in the yeast cell cycle where the cell becomes irreversibly committed to completing the cell cycle. START occurs in late G₁ and regulates entry into S phase. Sufficient translation initiation factors allow CLN3 translation when nutrients are abundant
Quiescent Cell Re-entry: Quiescent (G₀) cells re-enter the cell cycle after stimulation by growth factors.
Early Response vs. Delayed Response Genes: Early response genes encode transcription factors that stimulate transcription of delayed response genes, which include cyclins and CDKs. Early response gene expression doesn't need protein synthesis, but delayed response does.
Nondisjunction Checkpoint Failure: Failure of the chromosome-segregation checkpoint is most likely to cause nondisjunction.
p53 as a Tumor Suppressor: p53 arrests the cell cycle at G₁, S, or G₂ by inducing the transcription of p21, and may induce cell death in some circumstances when stabilized due to damaged DNA.
Unreplicated DNA and Mitosis: Unreplicated DNA prevents cells from entering mitosis through the inter-S checkpoint controls and ATR/Chk1 activation.
Centromeric Rec8 Role: In meiosis I, Rec8, a meiosis-specific homolog of Scc1, cleaves in chromosome arms to allow homologous chromosomes to separate. In meiosis II, Rec8 cleaves in the centromere to allow chromatids to separate.
Nuclear Envelope Breakdown: Nuclear envelope breakdown, involving the dephosphorylation of lamins is dependent on mitotic cyclins/cyclin-CDK complexes.
Anaphase A: Kinetochores remain attached to shortening kinetochore microtubules in anaphase A.
Anaphase B: The spindle poles move further apart during anaphase B (spindle elongates).

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Description

Test your knowledge on the intricacies of the eukaryotic cell cycle, focusing on stages, gene isolation, and cyclin regulation. Explore concepts such as the roles of kinetochores, centromeres, and regulatory mechanisms in cell division. This quiz covers essential topics for understanding cell biology and genetics.