1. The cell cycle consists of four main phases - G1, S, G2, and M phase. G1 is a growth phase where the cell prepares for DNA replication, S phase is where DNA replication occurs, G2 is a second growth phase where the cell prepares for mitosis, and M phase is mitosis and cytokinesis where the cell divides. 2. The cell cycle is regulated by cyclins and cyclin-dependent kinases (CDKs). Different cyclins partner with CDKs to control progression through the phases of the cell cycle. 3. p53, p21, and pRb play important roles in regulating the G1 to S phase transition.

1. Cell Cycle Presented by: Muhammad Asif Muhammad Asif Pu Pakistan

2. Cell Cycle Eric Niederhoffer SIU-SOM Muhammad Asif Pu Pakistan G1 G0 6-8 h DNA, RNA, Protein 3-4 h RNA, Protein 1 h Mitosis, Cytokinesis S G2 Cyc D’s CDK4,6 Cyc B/A CDK1 Cyc A CDK2 M Cyc E CDK2 6-12 h RNA, Protein p53 pRb Lamin H1 Abl

3. Variation in Cell Cycle Cyclins Cell cycle phases Cyclin-dependent kinases cyclins Muhammad Asif Pu Pakistan M G 1 G 2 S M G 1 Start D E A B(A) Cdk4 Cdk2 Cdk1

4. Cell Cycle Regulation pRb pRb CDK2 CE E2F Enzymes for DNA synthesis DNA damage 1. CDK phosphorylation 2. C degradation 3. C & CDK synthesis 4. CDK inhibition pRb Muhammad Asif Pu Pakistan Passage from G1 to S pRb P Active p53 p21

5. Review Questions What are and what happens during the phases of the cell cycle? Which proteins are involved in the regulation of the cell cycle? Which cyclins and cyclin-dependent kinases are most important in individual phases of the cell cycle? What are four mechanisms for regulating cyclin-dependent kinase activity? What role do p53, p21, and pRb play in the G1 to S transition? Muhammad Asif Pu Pakistan