All the following statements about destruction of cyclins are true EXCEPT: ubiquitin targets Cdks. destruction is carried out by proteasomes. ubiquitination occurs at specific sites on target molecules. destruction is preceded by polyubiquitination.

ubiquitin targets CDKs

Explanation:

Cyclins are named such because they undergo a constant cycle of synthesis and degradation during cell division. When cyclins are synthesized, they act as an activating protein and bind to Cdks forming a cyclin-Cdk complex. This complex then acts as a signal to the cell to pass to the next cell cycle phase.

Cyclins drive the events of the cell cycle by partnering with a family of enzymes called the cyclin-dependent kinases (Cdks). A lone Cdk is inactive, but the binding of a cyclin activates it, making it a functional enzyme and allowing it to modify target proteins.