Cell Cycle ControlsBiology 3 Kawashima

Philippine Science High SchoolSY 2009-2010

Key Terms and Concepts

• Checkpoints• Cyclins• Cyclin-dependent kinases

• 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

G1 Checkpoint

YES NO

G1 checkpoint

Continue with G1 and proceed to S

Exit cycle; switch to nondividing state

• 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

G2 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

M Phase Checkpoint

External Signals Affect Regulation

Stimulate cell division

•PDGF

Inhibit cell division

•Density dependence•Anchorage dependence