Question

A cell from a different person is found to have a mutation in the protein coding region resulting in Rb being unable to bind to the Cyclin/CDK complex. Would this mutation lead to an increased risk of cancer? Please explain in 1-2 sentences PROCESS: THE G, CHECKPOINT IS SUBJECT TO SOCIAL CONTROL Cyclin Cyclin Inactivating phosphate Cyclin Cak G, checkpoint passed Cyclin Cyclin Cdk Activating phosphate S-phase Growth factors Rb ATP ADP 1. Growth factors arrive from other cells. 2. Growth factors Cause Increase in cyclin and E2F concentrations. 3. Cyelin binds to Cdk; Cak is phosphorylated Rb Inactivates E2F by binding to it 4. Inactivating phosphate is removed, and active Cdk phosphorylates Rb. 5. Phosphorylated 6. E2F triggers Rb releases E2F production of S-phase proteins

Answer 1

Rb stands for Retinoblastoma. The product of the Rb gene plays a pivotal role in negative control of cell cycle by regulating the transcription of the genes necessary for entering into S phase, thereby acting as a G1/S phase checkpoint. They does this by binding and inhibiting the E2F family of transcription factors which regulates transcription of S phase genes.

When their is not a sufficient level of growth factor stimulus, the non-phosphorylated form of Rb protein binds to the E2F transcription factors and inactivates thereby preventing the transcriptionf of S-phase genes and making the cells stall at the G1 phase of the cell cycle rather than entering into the S phase. When the cell receives sufficient level of growth factor stimulus, the cyclins binds to its respective cyclin dependent kinases (CDK). The cyclin-CDK complex phosphorylates the Rb protein in the Rb-E2F complex. After phosphorylation, the Rb protein loses its affinity for E2F transcription factors. The E2F transcription factors is then set free to mediate its action as the transcription factors for the cell cycle progression from G1 phase to S phase.

If the mutation in the Rb gene affects its affinity for the E2F transcription factors, then the cell will progress into the S phase even though it is not ready for it. As the transcription of the S phase genes is not regulated in this case there will be an increased risk of cancer.