Break down of hydrogen bonds between nitrogenous bases of DNA is due to

Options

A. X-rays
B. UV-B
C. radiation
D. all the three

Answer

To answer the question regarding the breakdown of hydrogen bonds between nitrogenous bases of DNA, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding DNA Structure**:
- DNA is composed of two strands that are held together by hydrogen bonds between nitrogenous bases. The main bases are adenine (A), thymine (T), guanine (G), and cytosine (C). Adenine pairs with thymine, and guanine pairs with cytosine.

2. **Identifying the Factors**:
- The question asks what causes the breakdown of these hydrogen bonds. We need to consider various forms of radiation that can affect DNA.

3. **Types of Radiation**:
- **X-rays**: High-energy radiation that can penetrate tissues and cause damage to DNA, including breaking hydrogen bonds.
- **UV Rays**: Ultraviolet radiation from the sun can also cause damage to DNA. UVB rays are particularly known for causing skin cancer and can lead to the formation of pyrimidine dimers, disrupting the hydrogen bonds.
- **Gamma Rays**: Similar to X-rays, gamma rays are high-energy radiation that can cause significant damage to DNA.

4. **Conclusion**:
- All three types of radiation (X-rays, UV rays, and gamma rays) can lead to the breakdown of hydrogen bonds between nitrogenous bases in DNA. Therefore, the correct answer to the question is "all the three above".

### Final Answer:
The breakdown of hydrogen bonds between nitrogenous bases of DNA is due to X-rays, UV rays, and gamma rays. Therefore, the answer is all three.

---