Cell Cycle Regulation

Cyclin-dependent kinases (cdks)

kinases known to activate or deactivate proteins by adding phosphates to them (phosphorylation), inactive form always present in the cell, activated by cyclins, function dependent on specific cycliin binding at specific times (cyclin-cdks complex)

Cyclin + cdk complexes

switches correct machinery on/off, coordinates cell cycle steps, cyclins activates/inactivates protein kinases which act in phosphorylation, different cdks take cell through different check points

G1 phase regulation

production of cyclin D and E occurs, cdk-2 binds to cyclin E, cdk - 4 binds to cyclin D, RB (retinoblastoma protein) usually inhibits DNA replication, cdk 4 - cyclin D complex phosphorylates RB

S phase regulation

cyclin A produced, forms complex with cdk - 2, activates DNA replication, cyclin A degraded after, cdk - 2 inactive form stays

G2 phase regulation

cyclin B produced, forms complex with cdk - 1, activates mitosis, cyclin B degraded after, cdk - 1 inactive form stays

Proteins RB, P53, P21, P16

help regulate cell cycle

P53

binds to DNA to produce proteins, checks for DNA damage

P21

blocks progression of cell cycle, inhibits cdk - 4 + cyclin D function (inhibits activation of DNA replication + mitosis)

P16

inactivates cdks

50% of cancers

caused by defect in P53