The primary structure of a protein molecule has

Options

A. two ends
B. one end
C. three ends
D. no ends

Explanation

To answer the question regarding the primary structure of a protein molecule, we can follow these steps:

### Step-by-Step Solution:

1. **Definition of Primary Structure**: The primary structure of a protein refers to the specific linear sequence of amino acids in a polypeptide chain. This sequence is crucial as it determines the protein's overall structure and function.

2. **Amino Acids and Peptide Bonds**: The amino acids are linked together by peptide bonds, forming a long chain known as a polypeptide. Each amino acid in the sequence contributes to the protein's characteristics.

3. **Ends of the Polypeptide Chain**: A polypeptide chain has two distinct ends:
- **C-terminus**: This is the carboxyl end of the chain, where the last amino acid has a free carboxyl group (-COOH).
- **N-terminus**: This is the amino end of the chain, where the first amino acid has a free amino group (-NH2).

4. **Conclusion**: Therefore, the primary structure of a protein molecule has two ends: the C-terminus and the N-terminus.

5. **Correct Answer**: Based on the options provided (2 ends, 1 end, 3 ends, no end), the correct answer is **2 ends**.