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During the G1 checkpoint, the cell evaluates its internal environment before DNA replication. Which of the following proteins is most directly responsible for sensing DNA damage and halting the cell cycle at this point?

hard MCQ 3 marks Class 11 · Biology · Cell Cycle and Cell Division
  1. (a) p53
  2. (b) Cyclin E
  3. (c) CDK2
  4. (d) Rb
Answer
(a) p53

The correct answer is (a) p53 — Therefore, the correct answer is (a) p53.

Step-by-step solution

  1. The G1 checkpoint monitors cell size, growth signals, and DNA integrity.
  2. p53 is a transcription factor that is activated by DNA damage.
  3. Once activated, p53 induces the expression of p21, which inhibits CDKs.
  4. Inhibition of CDKs blocks progression into S phase.
  5. Thus, p53 is the key protein sensing DNA damage at G1.
  6. Other options like Cyclin E, CDK2, or Rb do not directly sense DNA damage.
  7. Therefore, the correct answer is (a) p53.
Common mistake: Selecting Rb as the sensor

Concept tested: G1 checkpoint proteins

Published · How this solution was prepared and checked

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