The document discusses checkpoints in the cell cycle that control progression from one phase to the next. It describes the G1, G2, and M phase checkpoints, noting that the G1 checkpoint determines whether cells continue cycling or enter quiescence, the G2 checkpoint is driven by maturation promoting factor allowing passage to mitosis, and the M phase checkpoint ensures proper chromosome attachment before anaphase. External signals and cyclins/cyclin-dependent kinases regulate progression through the checkpoints.

1. Cell Cycle Controls Biology 3 Kawashima Philippine Science High School SY 2009-2010

2. Key Terms and Concepts Checkpoints Cyclins Cyclin-dependent kinases

4. G1 Checkpoint Also known as “Restriction Point” in mammalian cells Cells that go through G1 usually complete the cell cycle Cells that do not receive the go-signal exit the cell cycle Quiescent non-dividing stage called G0 phase

5. G1 checkpoint Continue with G1 and proceed to S Exit cycle; switch to nondividing state

6. G2 Checkpoint MPF or maturation promoting factor drives the cell past the G2 checkpoint MPF is a protein complex composed of cyclins and cyclin-dependent kinases (Cdk) Accumulated cyclin in G2 associate with cyclin-dependent kinases

9. M Phase Checkpoint Ensures that chromosomes are properly attached to mitotic spindle (composed of microtubules) Anaphase promoting complex (APC) is inactive until kinetochores have interacted with microtubules Activation of APC indirectly triggers breakdown of cyclins

13. External Signals Affect Regulation