Question

1.List the functions of kinases and cyclins, and describe how they interact to cause cells to move through the cell cycle.

Answer 1

Protein kinases are enzymes that regulate the biological activity of proteins by phosphorylation of specific amino acids with ATP as the source of phosphate, thereby inducing a conformational from an inactive to active form of protein.

Cyclins are the proteins in the cytoplasm that fluctuate in concentration during the cell cycle. Increasing prior to mitosis and dropping off after mitosis. Cyclins regulates passage through the checkpoints before S, G1 and early events of mitosis.

CDK- complexes have variety of functions but CDKCs are most known for their role in cell cycle. Several different CDKs bind to Various cyclins to form CDKs . CDK1 the first human CDK to be identified associated with cyclin A or B. Cyclins A/B- CDK1 complexes drive the transition between G2 and M phase , as well as early M phase. The fluctuations control the activation of the cyclin-CDK complexes and the progression throughout the cell cycle.

G1 to S phase- CDKCs bind and phosphorylated members of the Rb protein. However, pRbs are also thought to repress the genes required in order for the transition from G1 phase to S phase- to occur. Once phosphorylation occurs transcriptional factors are then released to irreversibly inactive pRB and progression into the S phase- of the cell cycle.

G2 to M phase progression - at the end of S phase- cyclin A is associated with CDK1 and Cdk2 . Duriñg G2 phase , cyclin A is degraded, while cyclin B is synthesized and cyclin B - CDK1 complexes form. CDKs play a role in chromosomal condensation, fragmentation of Golgi network, breakdown of nuclear lamina . Inactivation of cyclin-B complex through the degradation of cyclin-B is necessary for exit out of the M phase of the cell cycle.