Which of the following radioisotopes is not suitable for DNA labelling based studies?

Options

A. `H^(3)`
B. `P^(32)`
C. `N^(15)`
D. `S^(35)`

Answer

To solve the question of which radioisotope is not suitable for DNA labeling based studies, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Components of DNA**:
- DNA is composed of three main components: a phosphate group, a pentose sugar (deoxyribose), and nitrogenous bases (adenine, thymine, cytosine, and guanine).

2. **Identify the Given Radioisotopes**:
- The options provided are H3 (Tritium), P32 (Phosphorus-32), N15 (Nitrogen-15), and H35 (Hydrogen-35).

3. **Analyze Each Radioisotope**:
- **H3 (Tritium)**: Tritium is a radioactive isotope of hydrogen. Since hydrogen is present in DNA (in the sugar and nitrogenous bases), H3 can be used for labeling.
- **P32 (Phosphorus-32)**: Phosphorus is a key component of the phosphate group in DNA. Therefore, P32 is suitable for DNA labeling.
- **N15 (Nitrogen-15)**: Nitrogen is found in the nitrogenous bases of DNA. Thus, N15 can also be used for labeling.
- **H35 (Hydrogen-35)**: This is another isotope of hydrogen. However, it is not commonly used for DNA labeling compared to Tritium (H3) due to its higher energy emissions and potential for causing damage.

4. **Identify the Unsuitable Radioisotope**:
- **Sulfur**: The question implies that one of the options is not suitable for DNA labeling. Sulfur is not a component of DNA. Therefore, any sulfur isotope, such as S35, would not be suitable for DNA labeling because there is no sulfur in the DNA structure to replace or attach to.

5. **Conclusion**:
- The radioisotope that is not suitable for DNA labeling is **H35** (or any sulfur isotope, if it were an option), as it does not have a corresponding component in DNA.

### Final Answer:
The radioisotope that is not suitable for DNA labeling based studies is **H35**.