Number of protein amino acids is

Options

A. 20
B. 16
C. 32
D. 64

Answer

To determine the number of protein amino acids, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Amino Acids**:
- Amino acids are organic compounds that contain an amino group (NH2), a carboxyl group (COOH), and a specific side chain that varies among different amino acids.

2. **Key Elements**:
- The key elements present in amino acids are Carbon (C), Hydrogen (H), Oxygen (O), and Nitrogen (N).

3. **Naturally Occurring Amino Acids**:
- While there are around 500 naturally occurring amino acids identified, not all of them are involved in protein synthesis.

4. **Protein Amino Acids**:
- Among these, only 20 amino acids are classified as proteinaceous or protein amino acids. These are the amino acids that are directly involved in the formation of proteins.

5. **Encoding of Amino Acids**:
- These 20 protein amino acids are encoded by triplet codons in the genetic code, which are known as standard amino acids.

6. **Classification of Amino Acids**:
- Out of the 20 protein amino acids, some are essential (9) and some are non-essential (11). Essential amino acids cannot be synthesized by the body and must be obtained through diet.

7. **Conclusion**:
- Therefore, the total number of protein amino acids is **20**.

### Final Answer:
The number of protein amino acids is **20**.

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