Question

When mitotic Cdk-cyclin is injected into cells that have just emerged from S phase, chromosome condensation and nuclear envelope breakdown occur immediately, rather than after the normal G2 delay of several hours.
Select the four correct statements.1. Mitotic Cdk-cyclin catalyzes the phosphorylation of condensins and lamins.
2. Mitotic Cdk-cyclin inhibits the phosphorylation of condensins and lamins.
3. It is possible to trigger chromosome condensation and nuclear envelope breakdown prematurely by experimentally introducing mitotic Cdk-cyclin into cells that have just emerged from G2 phase.
4. Phosphorylation of condensins and lamins contributes to chromosome condensation and nuclear envelope breakdown.
5. Mitotic Cdk-cyclin is normally activated at the end of S.
6. Phosphorylation of condensins and lamins prevents chromosome condensation and nuclear envelope breakdown.
7. It is possible to trigger chromosome condensation and nuclear envelope breakdown prematurely by experimentally introducing mitotic Cdk-cyclin into cells that have just emerged from S phase.
8. Mitotic Cdk-cyclin is normally activated at the end of G2.

Answer 1

Cdk-cyclin

Explanation:

Timing and all events of cell cycle is tightly regulated by a heterodimeric protein complex called Cdk-cyclin

Cyclin is the regulatory subunit which is bound to Cdk and activate them whereas Cdk is the catalytic subunit, cyclin bound Cdk becomes active and act as serine threonine kinase and phosphorylate target proteins

Cyclin-D-Cdk 4/6 is required for cell to enter in cell cycle, Cyclin-E-Cdk 2 is required for a cell to enter into S phase from G1, Cyclin-A-Cdk 2 is required for proper DNA replication and centrosome duplication and also induce disassembly of pre-replication complex and Cyclin-B-Cdk 1 is required for duplication of cell organelle and condensation of chromosomes

Therefore four correct statements are:

1. Mitotic Cdk-cyclin catalyzes the phosphorylation of condensins and lamins

2. Phosphorylation of condensins and lamins contributes to chromosome condensation and nuclear envelope breakdown

3. It is possible to trigger chromosome condensation and nuclear envelope breakdown prematurely by experimentally introducing mitotic Cdk-cyclin into cells that have just emerged from S phase

4. Mitotic Cdk-cyclin is normally activated at the end of G2