A molecular biologist analysed a nucleic acid sample and found that it contained the `N_(2)` bases in following proportion A=20%, T=15%, C=35%, G=30%. This data indicates that

Options

A. Nucleic acid in the sample is single stranded DNA
B. Nucleic acid in the smaple is double stranded DNA
C. Nucelic acid in the sample is double stranded RNA
D. Nucleic acid in the sample is single stranded RNA

Answer

To analyze the nucleic acid sample with the given proportions of nitrogenous bases (A = 20%, T = 15%, C = 35%, G = 30%), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Base Composition**:
- The sample contains:
- Adenine (A) = 20%
- Thymine (T) = 15%
- Cytosine (C) = 35%
- Guanine (G) = 30%

2. **Recall Chargaff's Rules**:
- Chargaff's rules state that in double-stranded DNA:
- The amount of adenine (A) equals the amount of thymine (T) (A = T).
- The amount of guanine (G) equals the amount of cytosine (C) (G = C).

3. **Check the A-T and G-C Ratios**:
- According to Chargaff's rules:
- If A = 20%, then T should also be 20%.
- If G = 30%, then C should also be 30%.
- In our sample:
- A = 20% and T = 15% (not equal)
- G = 30% and C = 35% (not equal)

4. **Conclusion about the DNA Structure**:
- Since the proportions of A and T, as well as G and C, do not match, this indicates that the nucleic acid cannot be double-stranded DNA.
- In single-stranded DNA or RNA, these ratios do not have to be equal.

5. **Determine the Type of Nucleic Acid**:
- The presence of thymine (T) indicates that the nucleic acid is DNA, not RNA (which contains uracil instead of thymine).
- Therefore, the nucleic acid must be single-stranded DNA.

### Final Answer:
The nucleic acid in the sample is single-stranded DNA.

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