Which of the following is not present in a nucleotide?

Options

A. Guanine
B. Cytosine
C. Adenine
D. Tyrosine

Explanation

To determine which of the following is not present in a nucleotide, we first need to understand the structure of a nucleotide. A nucleotide is the basic building block of nucleic acids, such as DNA and RNA. Each nucleotide consists of three main components:

1. **Nitrogenous Base**: This can be either a purine or a pyrimidine.
- **Purines**: Adenine (A) and Guanine (G)
- **Pyrimidines**: Cytosine (C), Thymine (T), and Uracil (U)

2. **Sugar**: There are two types of sugars found in nucleotides:
- **Ribose Sugar**: Found in RNA
- **Deoxyribose Sugar**: Found in DNA

3. **Phosphate Group**: This is a common component in all nucleotides.

Now, let's analyze the options provided:

- **Option A: Guanine** - Guanine is a nitrogenous base and is present in nucleotides.
- **Option B: Cytosine** - Cytosine is also a nitrogenous base and is present in nucleotides.
- **Option C: Adenine** - Adenine is another nitrogenous base and is present in nucleotides.
- **Option D: Tyrosine** - Tyrosine is an amino acid, not a component of nucleotides.

From this analysis, we can conclude that the correct answer is **Tyrosine**, as it is not present in a nucleotide.

### Final Answer:
**Tyrosine** is not present in a nucleotide.