Which of the following is a way that ionizing radiation can alter DNA structure?

• A. By increasing the rate of DNA methylation
• B. By substituting adenine for guanine during replication
• C. By promoting the formation of thymine dimers
• D. By causing double-strand breaks in the DNA backbone

Answer: (D)

Verified step by step guidance

1. Understand the concept of ionizing radiation: Ionizing radiation refers to high-energy radiation that can remove tightly bound electrons from atoms, creating ions. This type of radiation has enough energy to directly damage cellular components, including DNA.
2. Review the structure of DNA: DNA is composed of a double helix with a sugar-phosphate backbone and nitrogenous bases (adenine, thymine, cytosine, and guanine) paired through hydrogen bonds. Damage to the backbone or bases can disrupt its function.
3. Learn how ionizing radiation affects DNA: Ionizing radiation can cause double-strand breaks in the DNA backbone. These breaks occur when both strands of the DNA helix are severed, which can lead to mutations, chromosomal rearrangements, or cell death if not repaired properly.
4. Differentiate ionizing radiation effects from other types of DNA damage: For example, thymine dimers are caused by ultraviolet (UV) radiation, not ionizing radiation. Similarly, DNA methylation and base substitution are unrelated to the direct effects of ionizing radiation.
5. Conclude that the correct answer is 'By causing double-strand breaks in the DNA backbone,' as this is a specific and well-documented effect of ionizing radiation on DNA structure.