Cell Cycle pt.2
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42 Terms
What is MPF?
MPF is the Cdk1/Cyclin B complex that promotes entry into mitosis.
When is Cyclin B synthesized?
During G2 phase
How is MPF regulated?
Through cyclin production and phosphorylation/dephosphorylation of Cdk1.
What happens to Cyclin B when the cell exits mitosis?
It is degraded through ubiquitination and proteasomal degradation.
What stimulates Cyclin D production?
Growth factor signaling.
What is the restriction point?
A checkpoint in G1 where cells commit to progressing through the cell cycle.
What is the key target of Cdk4/6-Cyclin D?
The Rb/E2F complex.
What is the function of Rb?
Rb is a tumor suppressor that arrests cell cycle progression by inhibiting E2F.
What is E2F?
A transcription factor that activates genes needed for cell cycle progression.
What happens when E2F is activated?
It stimulates transcription of Cyclin E and DNA synthesis proteins.
What is the role of Cyclin E?
It helps cells enter S phase through activation of Cdk2.
What inhibits the Cdk2/Cyclin E complex?
The cyclin-dependent kinase inhibitor p27.
What does CKI stand for?
Cyclin-dependent kinase inhibitor.
How is p27 inhibition overcome?
Repression of p27 synthesis and phosphorylation leading to its degradation.
How do growth factors help repress p27 synthesis?
Through Erk and Akt signaling pathways.
What is the role of APC/C in Cyclin E regulation?
Its inactivation prevents Cyclin E degradation.
What are ATM and ATR?
Protein kinases activated by DNA damage.
What is the purpose of DNA damage checkpoints?
To prevent damaged DNA from being passed to daughter cells.
What happens when ATM and ATR are activated?
They activate checkpoint kinases called Chk.
How do Chk kinases arrest the cell cycle?
They block phosphatases needed to activate Cdks.
What is the function of Cdc25?
A phosphatase required to activate Cdk1 and Cdk2.
What is the role of Chk2 in DNA damage response?
It helps phosphorylate and stabilize p53.
What is p53?
A tumor suppressor that arrests the cell cycle in response to DNA damage.
How does p53 cause cell cycle arrest?
It stimulates transcription of the CKI p21
What happens if DNA damage cannot be repaired?
p53 induces transcription of proteins that lead to apoptosis.
What can happen when p53 is mutated?
Cells may fail to arrest in response to DNA damage.
What is the role of MPF during mitosis?
It promotes entry into mitosis and activates proteins needed for mitotic events.
What are Aurora and Polo?
Mitotic protein kinases that are targets of Cdk1.
What is the function of cohesins?
They hold sister chromatids together during and after DNA replication.
What happens to cohesins during mitotic entry?
Most are phosphorylated and dissociate
What is the function of condensins?
They compress chromosomes by forming DNA loops.
What is the difference between cohesin and condensin?
Cohesin holds two sister chromatids together; condensin compresses an individual chromatid.
How does the nuclear envelope break down?
MPF phosphorylates nuclear lamina intermediate filaments
What is the metaphase plate?
The plane where chromosomes align during metaphase.
What does the spindle assembly checkpoint monitor?
Whether all chromosomes are properly attached to spindle microtubules.
What is the mitotic checkpoint complex (MCC)?
A group of kinetochore proteins that inhibits APC/C.
Why does the spindle assembly checkpoint inhibit APC/C?
To prevent anaphase until all chromosomes are properly attached to the spindle.
What happens when Cdc20 is released from the MCC?
It activates APC/C.
What proteins are targeted for degradation by APC/C during the metaphase-to-anaphase transition?
Cyclin B and securin.
What is the function of securin?
It inhibits separase.
What does separase do?
It is a protease that degrades cohesin
How does cytokinesis occur in animal cells?
A contractile ring of actin and myosin II forms beneath the plasma membrane and divides the cell.