Control of the Cell Cycle quiz #1 Flashcards
Control of the Cell Cycle quiz #1
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What roles do cyclins and cyclin-dependent kinases (CDKs) play in controlling the cell cycle, and how do their concentrations differ throughout the cycle?
Cyclins are proteins that regulate the cell cycle by binding to and activating cyclin-dependent kinases (CDKs), which then phosphorylate target proteins to control cell cycle events. Cyclin concentrations fluctuate at different stages of the cell cycle, peaking at specific phases to regulate transitions, while CDK concentrations remain constant but are only active when bound to cyclins. What are the main checkpoints in the cell cycle, and what does each checkpoint monitor before allowing the cell to proceed?
The main checkpoints are the G1 checkpoint (checks cell size, nutrients, growth factors, and DNA damage), the S checkpoint (ensures DNA replication is complete and accurate), the G2 checkpoint (verifies DNA replication and repairs any damage before mitosis), and the M checkpoint (spindle checkpoint, ensures chromosomes are properly attached to spindle fibers before separation). Describe three mechanisms by which cyclin-dependent kinase (CDK) activity is regulated during the cell cycle.
CDK activity is regulated by: (1) inhibitory phosphorylation, where a specific phosphate must be removed by cdc25 to activate the CDK; (2) binding of CDK inhibitors, which block CDK function; and (3) regulation of cyclin levels, where cyclins are degraded (e.g., by the anaphase promoting complex) when no longer needed, thus inactivating CDKs. What is the primary function of cyclins in the cell cycle?
Cyclins regulate the cell cycle by binding to and activating cyclin-dependent kinases (CDKs), which then phosphorylate target proteins to control cell cycle events. How do the concentrations of cyclins and CDKs differ throughout the cell cycle?
Cyclin concentrations fluctuate and peak at specific phases to regulate transitions, while CDK concentrations remain constant but are only active when bound to cyclins. What does the G1 checkpoint monitor before allowing the cell to proceed to S phase?
The G1 checkpoint checks for cell size, nutrient availability, growth factors, and DNA damage before allowing the cell to proceed. What is the main role of the S checkpoint in the cell cycle?
The S checkpoint ensures that DNA replication is complete and accurate before the cell continues to the next phase. Describe one mechanism by which CDK activity is inhibited during the cell cycle.
CDK activity can be inhibited by the addition of an inhibitory phosphate, which must be removed by the cdc25 protein for activation. How does the anaphase promoting complex (APC) regulate cyclin levels?
The APC labels cyclins with ubiquitin for degradation, especially M and S cyclins, thus inactivating CDKs when cyclins are no longer needed. What is the function of CDK inhibitors in cell cycle regulation?
CDK inhibitors are proteins that bind to CDKs (often in complex with cyclins) and block their function, preventing progression through the cell cycle.
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