Deamination is the first step in urea formation. It means the

Options

A. Reduction of ammonia
B. Oxidation of ammonia
C. Addition of amino group to a non-amino organic molecule
D. Removal of amino group from an amino acid

Answer

### Step-by-Step Solution:

1. **Understanding Deamination**: Deamination is a biochemical process that involves the removal of an amino group from an amino acid. This is a crucial step in the metabolism of amino acids, particularly in the formation of urea.

2. **Identifying the Process**: In the context of urea formation, deamination is the first step. It occurs primarily in the liver, where amino acids are broken down, and their amino groups are removed.

3. **Recognizing the Components**: During deamination, the amino group (NH2) is separated from the amino acid, resulting in the formation of ammonia (NH3) and a corresponding keto acid.

4. **Linking to Urea Cycle**: After deamination, the ammonia produced is toxic and must be converted into a less harmful substance. This conversion occurs through the urea cycle (also known as the ornithine cycle), which takes place in the liver and kidneys.

5. **Evaluating the Options**:
- **Option 1**: Reduction of ammonia - Incorrect, as deamination does not involve reducing ammonia.
- **Option 2**: Oxidation of ammonia - Incorrect, as oxidation is not part of the deamination process.
- **Option 3**: Addition of amino group to a non-amino organic molecule - Incorrect, as deamination involves removal, not addition.
- **Option 4**: Removal of amino group from an amino acid - Correct, as this accurately describes the process of deamination.

6. **Conclusion**: The correct answer to the question "Deamination is the first step in urea formation. It means the" is the removal of amino group from an amino acid.