Answer :
Answer:
A. Cyclins
Explanation:
Cyclins are group of related proteins and are the most important core cell cycle regulators. Each cyclin is associated with a particular transition or phase in the cell cycle and helps drive the events of that phase or period by partnering with a family of enzymes called the cyclin-dependent kinases (Cdks).
Cdks are kinases, enzymes that phosphorylate (attach phosphate groups to) specific target proteins. The apg acts like a switch, making the target less active or to have more protein. When cyclin attaches to Cdk, it can activate the Cdk as a kinase and can directs also the Cdk to a specific set of target proteins. For example, G1/S cyclins send Cdks to S phase targets (e.g., DNA replication), while M cyclins send Cdks to M phase targets (e.g.,breakdown of the nuclear membrane ).