**Core Concept**
The component of a cell most affected by radiation is its DNA, specifically the genetic material within the nucleus. Radiation-induced damage to DNA can lead to mutations, chromosomal aberrations, and cell death, ultimately affecting the cell's ability to proliferate and function normally.

**Why the Correct Answer is Right**
Radiation can cause direct damage to DNA by breaking the phosphodiester backbone, forming DNA-DNA and DNA-protein crosslinks, and inducing base damage. This damage can be further exacerbated by the formation of reactive oxygen species (ROS) and the activation of repair pathways, which can sometimes lead to the incorrect repair of DNA lesions. The genetic material within the nucleus is particularly susceptible to radiation-induced damage due to its high metabolic activity and the presence of essential enzymes and repair machinery.

**Why Each Wrong Option is Incorrect**
**Option A:** Mitochondria are not the primary target of radiation damage, although they can be affected indirectly by the formation of ROS.

**Option B:** The cell membrane is not the most susceptible component to radiation damage, as it is relatively resistant to ionizing radiation.

**Option C:** The cytoskeleton is not directly affected by radiation, although changes in cell shape and morphology can occur as a secondary effect of radiation-induced DNA damage.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the effects of radiation on cells can be dose-dependent, with low doses causing minimal damage, while high doses can lead to significant DNA damage and cell death. This is a critical concept in radiation oncology and the treatment of cancer.

**Correct Answer:** D. DNA.