The Cell Cycle #lec3 Flashcards
What initiates the positive feedback loop in cell-cycle transitions?
An external trigger mechanism must first unleash the feedback loop.
How do S-Cdks contribute to Cdc25 activation?
Active S-Cdks in G2 and early prophase help initiate Cdc25 activation.
What is the relationship between M-Cdk and PP2A-B55?
M-Cdk and PP2A-B55 are mutual antagonists, producing another layer of positive feedback.
What do highly integrated feedback systems generate?
They generate a robust biochemical switch that can operate even when some components fail.
What triggers the metaphase-to-anaphase transition?
The Anaphase-promoting Complex/Cyclosome (APC/C) triggers the transition through protein destruction.
What role does APC/C play in anaphase?
APC/C catalyzes the ubiquitylation and destruction of securin and S- and M-cyclins.
What happens to securin during metaphase?
Its destruction activates a protease that separates sister-chromatid pairs, unleashing anaphase.
How does APC/C activity change during mitosis?
APC/C activity increases in mid-mitosis and remains high through G1.
What activates APC/C–Cdc20 and inhibits APC/C–Cdh1?
Phosphorylation by M-Cdk activates APC/C–Cdc20 and inhibits APC/C–Cdh1.
What is the role of SCF in the cell cycle?
SCF ubiquitylates certain CKI proteins in late G1 and destroys G1/S-cyclins in early S phase.
How is SCF activity different from APC/C activity?
SCF activity is constant during the cell cycle, while APC/C activity varies.
What is a key regulatory event in late M phase?
The inactivation of Cdks resets the cell-cycle control system.
What generates a stable G1 gap phase?
Cdk inactivity generates a stable G1 gap phase during which the cell grows and monitors its environment.
What mechanisms suppress Cdk activity after mitosis?
One mechanism is the late mitotic activation of APC/C–Cdh1; another is increased production of CKIs.
How does decreased transcription of M-cyclin genes affect Cdk activity?
It helps reduce M-Cdk activity in late mitosis.
What does the cell-cycle control system consist of?
It consists of a linked series of biochemical switches that drive stepwise progression through the phases of the cell cycle.
