Question:easy
Which of the following is the most radiosensitive phase of the cell cycle?
Which of the following is the most radiosensitive phase of the cell cycle?
Show Hint
Cells caught mid-division, with condensed chromatin and no time to repair, are hit hardest by radiation.
Updated On: Jul 8, 2026
- G1
- S
- G2
- M
Show Solution
The Correct Option is D
Solution and Explanation
Step 1: Understanding the Concept:
Radiosensitivity changes across the cell cycle because the cell's ability to repair DNA damage and the state of its chromatin both change from phase to phase.
Step 2: Key Formula or Approach:
Think of it in terms of repair opportunity. Whichever phase gives the cell the least time or tools to fix damaged DNA before something critical happens (like chromosome separation) will be the most sensitive phase, and whichever phase gives the most repair capacity will be the most resistant.
Step 3: Detailed Explanation:
In late S phase, a fresh copy of DNA sits right next to the original strand, so homologous recombination repair works efficiently, making this the most radioresistant window. G1 has moderate sensitivity. G2 is fairly sensitive as the cell readies its machinery for division. M phase is where the chromatin is packed tightly into chromosomes and the cell is committed to dividing with essentially no pause for repair, which is why it takes the biggest hit from radiation and is ranked the most radiosensitive phase overall.
Step 4: Final Answer:
The M phase of the cell cycle is the most radiosensitive, since dividing cells with condensed chromatin have the least chance to repair radiation damage.
Radiosensitivity changes across the cell cycle because the cell's ability to repair DNA damage and the state of its chromatin both change from phase to phase.
Step 2: Key Formula or Approach:
Think of it in terms of repair opportunity. Whichever phase gives the cell the least time or tools to fix damaged DNA before something critical happens (like chromosome separation) will be the most sensitive phase, and whichever phase gives the most repair capacity will be the most resistant.
Step 3: Detailed Explanation:
In late S phase, a fresh copy of DNA sits right next to the original strand, so homologous recombination repair works efficiently, making this the most radioresistant window. G1 has moderate sensitivity. G2 is fairly sensitive as the cell readies its machinery for division. M phase is where the chromatin is packed tightly into chromosomes and the cell is committed to dividing with essentially no pause for repair, which is why it takes the biggest hit from radiation and is ranked the most radiosensitive phase overall.
Step 4: Final Answer:
The M phase of the cell cycle is the most radiosensitive, since dividing cells with condensed chromatin have the least chance to repair radiation damage.
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