Question

For CDK2 to be active which cyclin must be elevated?

A) Cyclin A
B) Cyclin B
C) Cyclin D
D) Cyclin E

Answer 1

CDK2 becomes active when it is bound to cyclin E, and the Cdk/cyclin complex must also be phosphorylated for full activation. Cyclin levels fluctuate throughout the cell cycle, relevant to the phases of cell division, with cyclin E enabling progression through the G1/S checkpoint.

Step-by-step explanation:

For CDK2 to be active, cyclin E must be elevated. Cyclins are regulatory proteins that control the progression of cells through the cell cycle, and they achieve this control by binding with cyclin-dependent kinases (Cdks). The function of cyclins is to activate Cdks, as Cdks are inactive unless bound to the correct cyclin.

Cyclins A, B, D, and E each bind to different Cdks and serve different roles at various points in the cell cycle. For instance, cyclin E binds with CDK2 at the G1/S checkpoint, facilitating progression into the DNA synthesis phase. In contrast, cyclin D typically associates with CDK4 or CDK6, playing a role earlier in the G1 phase of cell division.

It is also important to note that the Cdk/cyclin complex requires phosphorylation to become fully active. This post-translational modification alters the shape of the protein and can activate or de-energize its function. Cyclin E, therefore, has to bind to CDK2 and then be phosphorylated to become fully operational.