DNA differs from RNA in having

Options

A. Cytosine but no guanine
B. Thymine but no uracil
C. Uracil but no thymine
D. Thymine but no cytosine.

Answer

To answer the question "DNA differs from RNA in having," we need to analyze the components of DNA and RNA, particularly focusing on their nitrogenous bases.

### Step-by-Step Solution:

1. **Identify the Components of DNA and RNA**:
- DNA (Deoxyribonucleic Acid) contains the sugar deoxyribose.
- RNA (Ribonucleic Acid) contains the sugar ribose.

2. **List the Nitrogenous Bases**:
- Both DNA and RNA have four nitrogenous bases, but they differ in one base.
- The nitrogenous bases are:
- **Purines**: Adenine (A) and Guanine (G)
- **Pyrimidines**: Cytosine (C), Thymine (T) in DNA, and Uracil (U) in RNA.

3. **Compare the Bases**:
- In DNA, the bases are Adenine (A), Thymine (T), Cytosine (C), and Guanine (G).
- In RNA, the bases are Adenine (A), Uracil (U), Cytosine (C), and Guanine (G).

4. **Identify the Key Difference**:
- The main difference between DNA and RNA is that DNA contains Thymine (T) while RNA contains Uracil (U).
- Therefore, DNA has Thymine but does not have Uracil.

5. **Evaluate the Options**:
- The options given are:
- A) Cytosine but no Guanine
- B) Thymine but no Uracil
- C) Uracil but no Thymine
- D) Thymine but no Cytosine
- From our analysis, we can see that:
- Option A is incorrect because both Cytosine and Guanine are present in DNA.
- Option B is correct because DNA has Thymine but no Uracil.
- Option C is incorrect because Uracil is not present in DNA.
- Option D is incorrect because both Thymine and Cytosine are present in DNA.

6. **Conclusion**:
- The correct answer is that DNA differs from RNA in having **Thymine but no Uracil**.