Which of the following is a basic amino acid?

Options

A. Serine
B. Alanine
C. Tyrosine
D. Lysine

Answer

To determine which of the given amino acids is a basic amino acid, we need to understand the definition of basic amino acids and analyze the structures of the provided options.

### Step-by-Step Solution:

1. **Definition of Basic Amino Acids**:
Basic amino acids are those that have an additional amino group (-NH2) in their side chain. This extra amino group contributes to the basic character of the amino acid.

2. **Analyzing the Options**:
Let's analyze the structures of the amino acids provided in the options. We will look for the presence of an additional amino group in the side chain.

3. **Option 1: (Assumed to be Glycine)**:
- Structure: H2N-CH2-COOH
- Analysis: Glycine has one amino group and one carboxylic group, but no additional amino group in the side chain. Therefore, it is **not a basic amino acid**.

4. **Option 2: (Assumed to be Alanine)**:
- Structure: H2N-CH(CH3)-COOH
- Analysis: Alanine has one amino group and one carboxylic group, with a methyl group (CH3) as the side chain. There is no additional amino group. Therefore, it is **not a basic amino acid**.

5. **Option 3: (Assumed to be Tyrosine)**:
- Structure: H2N-CH(C6H5OH)-COOH
- Analysis: Tyrosine has one amino group and one carboxylic group, with a phenolic side chain (C6H5OH). There is no additional amino group. Therefore, it is **not a basic amino acid**.

6. **Option 4: Lysine**:
- Structure: H2N-CH2-CH2-CH2-NH2-COOH
- Analysis: Lysine has one amino group and one carboxylic group, plus an additional amino group in its side chain (NH2). This extra amino group gives lysine its basic character. Therefore, **lysine is a basic amino acid**.

7. **Conclusion**:
Based on the analysis, the amino acid that qualifies as a basic amino acid is **Lysine**.

### Final Answer:
Lysine is the basic amino acid among the given options.

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