Final answer:
Mechanisms to prevent a Cdk from phosphorylating its target protein include phosphorylation by Wee-1 and binding of Cdk inhibitors to the Cdk, not dephosphorylation by Cdc-25 which activates the Cdk.
The correct answer to which mechanisms could prevent a Cdk from phosphorylating its target protein is d. a and b (but not c).
Step-by-step explanation:
To determine the mechanisms that may be used to prevent a Cyclin-dependent kinase (Cdk) from phosphorylating its target protein, we should understand how Cdks function and how their activity can be regulated. Activation of Cdks requires their binding to cyclin and being phosphorylated at specific sites. However, there are inhibitors that can prevent the activation of Cdks, thus controlling the cell cycle progression.
The available options are: a. phosphorylation by Wee-1, which adds an inhibitory phosphate group to the Cdk, b. binding of Cdk inhibitors (CKI) to the Cdk, which prevents the kinase from accessing its substrates, and c. dephosphorylation by Cdc-25, which actually removes an inhibitory phosphate group and therefore activates the Cdk, rather than inhibiting it.
From these mechanisms, both a and b serve as inhibitors, while c is an activator. Therefore, the correct answer to which mechanisms could prevent a Cdk from phosphorylating its target protein is d. a and b (but not c).