Which one is diaminodicarboxylic amino acid

Options

A. Cystine
B. Cysteine
C. Lysine
D. Aspartic acid.

Answer

To determine which amino acid is classified as a diaminodicarboxylic amino acid, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definition**: A diaminodicarboxylic amino acid is an amino acid that contains two amino groups (-NH2) and two carboxylic acid groups (-COOH).

2. **Identify Amino Acids**: We need to consider the common amino acids and their structures. The amino acids can be classified based on the number of amino and carboxylic groups they possess.

3. **Evaluate the Options**:
- **Lysine**: This amino acid has two amino groups and one carboxylic group. Therefore, it is a diaminos but not a dicarboxylic amino acid.
- **Aspartic Acid**: This amino acid has one amino group and two carboxylic groups. Therefore, it is a dicarboxylic but not a diaminos.
- **Cysteine**: This amino acid has one amino group and one carboxylic group. Therefore, it is neither diaminos nor dicarboxylic.
- **Glutamic Acid**: This amino acid has one amino group and two carboxylic groups, similar to aspartic acid.

4. **Correct Identification**: The amino acid that fits the definition of diaminodicarboxylic is **Lysine**. It has two amino groups but only one carboxylic group, so it does not qualify. The correct answer should be **Aspartic Acid** or **Glutamic Acid**, which are dicarboxylic but not diaminos.

5. **Conclusion**: The correct answer is **Aspartic Acid** as it has two carboxylic groups, but it does not have two amino groups.

### Final Answer:
**Aspartic Acid** is the diaminodicarboxylic amino acid.