Which phase of the cell cycle is the most sensitive to radiation?

The M phase, also known as mitosis, is the most sensitive phase of the cell cycle to radiation exposure. This heightened sensitivity is primarily due to the processes occurring during mitosis, where the cell is undergoing division and the chromosomes are highly condensed and organized for segregation. During this phase, DNA is most susceptible to damage from radiation, as the cell is actively replicating and distributing its genetic material.

When radiation interacts with the DNA during mitosis, it can cause double-strand breaks, which are particularly harmful. If these breaks are not properly repaired before the cell completes division, it can lead to cell death, mutations, or the potential development of cancer. The risk of error is highest during this phase compared to other phases of the cell cycle.

In contrast, while the G1 and G2 phases also present opportunities for radiation damage, cells are not undergoing division, and DNA repair mechanisms are more actively engaged. The S phase is also less sensitive than mitosis because, although DNA replication occurs, the DNA is not as condensed as during mitosis, making it less vulnerable to radiation-induced damage. Hence, the M phase's dynamics of active chromosomal segregation make it the most sensitive to radiation effects.