Question

For a cyclin-Cdk complex to be maximally active, it has to be phosphorylated at one site by a specific protein kinase and dephosphorylated at other sites by specific protein phosphatases. True or False?

Answer 1

The statement is True; for full activity, the cyclin-Cdk complex requires precise phosphorylation and dephosphorylation at specific sites for regulation during the cell cycle.

Step-by-step explanation:

The statement that a cyclin-Cdk complex must be phosphorylated at a specific site by a protein kinase and dephosphorylated at different sites by specific protein phosphatases to be maximally active is True. Cyclins and cyclin-dependent kinases (Cdks) are essential for the progression of the cell through its cycle. Cyclins must bind to Cdks to form an active complex.

The levels of Cdk proteins are usually constant, but the concentration of cyclins varies, which leads to the formation of the Cdk/cyclin complexes that are crucial for cell cycle regulation. To fully activate the Cdk/cyclin complex, it must be phosphorylated by another kinase. However, it is also true that dephosphorylation at certain sites is necessary for full activation, implying that both phosphorylation and dephosphorylation are key regulatory steps for the activity of the Cdk/cyclin complex.