Which of the following is not present in nucleotide?

Options

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

Answer

To determine which of the following is not present in a nucleotide, we need to first understand the structure of a nucleotide. A nucleotide is composed of three main components:

1. **A phosphate group**
2. **A sugar molecule** (deoxyribose in DNA and ribose in RNA)
3. **A nitrogenous base** (which can be adenine, guanine, cytosine, thymine, or uracil)

Now, let's analyze the options given in the question:

1. **Cytosine** - This is a nitrogenous base that is present in nucleotides.
2. **Guanine** - This is another nitrogenous base that is present in nucleotides.
3. **Adenine** - This is also a nitrogenous base found in nucleotides.
4. **Thymine** - This is a nitrogenous base present in DNA nucleotides.
5. **Tyrosine** - This is an amino acid and is not a component of nucleotides.

From the analysis, we can conclude that **tyrosine** is not present in nucleotides.

Thus, the correct answer is **option D: Tyrosine**.

### Step-by-Step Solution:
1. **Identify the components of a nucleotide**: A nucleotide consists of a phosphate group, a sugar, and a nitrogenous base.
2. **List the nitrogenous bases**: The nitrogenous bases include adenine, guanine, cytosine, thymine (in DNA), and uracil (in RNA).
3. **Evaluate the options**: Check each option to see if it is a component of a nucleotide.
4. **Identify the incorrect option**: Recognize that tyrosine is an amino acid, not a component of a nucleotide.
5. **Conclude the answer**: The answer is option D: Tyrosine.