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Quiz 18/19

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Justine C.

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10 Questions

What is the role of the kinase Wee1?

it phosphorylates M-Cdk to inactivate it

The anaphase-promoting complex (APC) triggers the onset of anaphase by:

triggering the destruction of Cohesins that hold the sister chromatids together.

The activation of M-Cdk begins abruptly, mainly because:

M-cyclin is bound to M-Cdk and the complex dephosphorylated by Cdc25

What process is necessary in llate G1 phase to transition to S phase?

extracellular signals (mitogens) are activated

Place the cell cycle in the correct order.


What would be the consequence of a Wee1 gene mutation that prevents the protein from being translated?

it would keep the M-cyclin/M-Cdk complex active

Which cell cycle phase is the shortest?

M phase

Meiosis I has which feature?

All of the above

The nuclear envelope breaks down at the start of prometaphase because:

Lamins are phosphorylated, which leads to filament dissociation.

Which event triggers a pause in G1 phase?

the presence of DNA damage

Study Notes

Cell Cycle Regulation

  • Wee1 kinase inhibits M-Cdk activation, ensuring that mitosis is delayed until the DNA is fully replicated and checked for errors.

Anaphase Onset

  • The anaphase-promoting complex (APC) triggers the onset of anaphase by ubiquitinating and degrading securin, which releases separase to cleave cohesion, allowing sister chromatids to separate.

M-Cdk Activation

  • M-Cdk activation begins abruptly because Wee1 kinase, which inhibits M-Cdk, is inactivated, and Cdc25, which activates M-Cdk, is activated.

G1 Phase Transition

  • The transition from G1 to S phase requires the activation of S-Cdk, which phosphorylates and inhibits Rb, allowing E2F to activate transcription of genes necessary for DNA replication.

Cell Cycle Order

  • The correct order of the cell cycle is: G1 → S → G2 → M.

Wee1 Gene Mutation

  • A Wee1 gene mutation that prevents the protein from being translated would lead to uncontrolled M-Cdk activation, causing premature entry into mitosis, which can result in chromosomal instability and cancer.

Cell Cycle Phases

  • The shortest phase of the cell cycle is mitosis (M phase).

Meiosis I Feature

  • Meiosis I is characterized by the reductional division, where the number of chromosomes is halved.

Nuclear Envelope Breakdown

  • The nuclear envelope breaks down at the start of prometaphase because of phosphorylation of lamin by M-Cdk, allowing chromatin to condense and interact with the mitotic spindle.

G1 Phase Pause

  • A pause in G1 phase can be triggered by the presence of DNA damage or other cellular stresses, which activate the p53 tumor suppressor protein to induce cell cycle arrest.

This quiz covers the regulation of the cell cycle, including the role of Wee1 kinase, M-Cdk activation, and the anaphase-promoting complex (APC) in delaying mitosis until DNA replication and error checking are complete.

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