Which of the following bases is not present in DNA?

Options

A. Adenine
B. Thymine
C. Cytosine
D. Uracil

Explanation

To determine which of the following bases is not present in DNA, we need to analyze the options provided: adenine, thymine, cytosine, and uracil.

### Step-by-Step Solution:

1. **Understanding DNA Structure**:
- DNA, or deoxyribonucleic acid, is a type of nucleic acid that consists of long chains of nucleotides.
- Each nucleotide is made up of three components: a nitrogenous base, a pentose sugar (deoxyribose in the case of DNA), and a phosphate group.

2. **Identifying Nitrogenous Bases in DNA**:
- The nitrogenous bases found in DNA are:
- Adenine (A)
- Thymine (T)
- Cytosine (C)
- Guanine (G)
- Therefore, the four bases present in DNA are adenine, thymine, cytosine, and guanine.

3. **Comparing with RNA**:
- RNA, or ribonucleic acid, also consists of nucleotides but has a slightly different composition.
- The nitrogenous bases in RNA are:
- Adenine (A)
- Uracil (U) - replaces thymine
- Cytosine (C)
- Guanine (G)

4. **Identifying the Odd One Out**:
- From the options given (adenine, thymine, cytosine, uracil), we can see that:
- Adenine, thymine, and cytosine are all present in DNA.
- Uracil is not present in DNA; it is found in RNA instead.

5. **Conclusion**:
- Therefore, the base that is not present in DNA is **uracil**.

### Final Answer:
The base that is not present in DNA is **uracil**.