Question

Which of the following are positive regulators of cell cycle?

• A. Cyclin and cyclin dependent kinases
• B. Retinoblastoma protein
• C. P53
• D. P21

Hint:

• Positive cell cycle regulators promote progression (e.g., Cyclins, CDKs).
• Negative cell cycle regulators inhibit progression (e.g., Rb, p53, p21, p16).
• Many negative regulators are tumor suppressor proteins.

Answer 1

The Correct Option is A

In the context of the cell cycle, positive regulators are molecules that promote progression through the cycle. Among the options provided, we need to identify which functions as a positive regulator:

Cyclin and cyclin dependent kinases (CDKs): These proteins work together as crucial positive regulators. Cyclins bind to CDKs, activating them to phosphorylate target proteins that initiate and regulate various phases of the cell cycle, promoting cell division and progression.

Retinoblastoma protein (Rb): This protein is a negative regulator. It inhibits cell cycle progression by preventing the transcription of genes necessary for S phase entry in its unphosphorylated state.

P53: Known as the "guardian of the genome," p53 is a negative regulator. It can lead to cell cycle arrest or apoptosis in response to DNA damage.

P21: This protein is a cyclin-dependent kinase inhibitor. Induced by p53, it acts as a negative regulator, hindering the activity of cyclin-CDK complexes, thereby arresting the cell cycle.

Therefore, the correct answer is Cyclin and cyclin dependent kinases, as they actively drive the cell cycle forward.