Question

9. Which form of retinoblastoma must be achieved to promote cell cycle to the S phase? A. dephosphorylated B. hypophosphorylated C. hyperphosphorylated D. hypophosphorylated or hyperphosphorylated depending on the type of the cell Describe the process of passing check point G1 during a cell cycle. 10. Which hormone may induce cellular signal only by binding to the receptor which is express on the plasma membrane? A. Erythropoietin B. Estrogen C. Cortisol D. DHEA Describe the process of genomic action of the steroid hormons.

Answer 1

9: Answer : Option C: Hyperphosphorylated.

The retinoblastoma protein is a substrate for CDK (cyclin dependent kinases). CDK phosphorylate the retinoblastoma protein and the resulting phosphorylated retinoblastoma protein can not block the entry of cell from G1 to S phase.
When retinoblastoma protein is unphosphorylated, it binds to transcription factor E2F. The bound E2F can not serve in upregulation of the genes for DNA replication. So, the cell can not proceed from G1 to S phase. The retinoblastoma protein is unphosphorylation when there is any DNA damage and the cell can not pass through G1 check point. Any damage to DNA is detected by protein kinases. These protein kinases serve to inhibit the cyclin E- CDK. The inhibited CDK can not phosphorylate retinoblatoma which in turn then block the entry of cell into S phase.