Final answer:
p21 is the Cdk inhibitor that is controlled by p53, and it helps to prevent cells with damaged DNA from proceeding with the cell cycle by inhibiting Cyclin-dependent kinases.
Step-by-step explanation:
The molecule that acts as a Cdk inhibitor and is controlled by the p53 tumor suppressor protein is p21. The role of p53 is crucial when there is damaged DNA in cells at the G1 checkpoint of the cell cycle. Upon detecting damaged DNA, p53 functions to halt the cell cycle by increasing the production of p21, which then binds to and inhibits Cyclin-dependent kinases (Cdks), preventing the cell from progressing to the S phase of the cell cycle. In the situation where DNA cannot be repaired, p53 can trigger apoptosis to ensure that damaged genetic material is not passed on during cell division. Thus, among the options provided, p21 is the correct answer as the Cdk inhibitor that is controlled by p53.