In primary structure a protein is imagined as a line, the left end represents :-

Options

A. The first amino acid and its carboxyl terminal
B. The last amino acid and its carboxyl terminal
C. The first amino acid and its amino terminal
D. The last amino acid and its amino terminal

Answer

To answer the question about the primary structure of a protein and what the left end represents, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Primary Structure**:
- The primary structure of a protein refers to its linear sequence of amino acids. This sequence is crucial as it determines the protein's overall structure and function.

2. **Identifying Ends of the Protein**:
- In a linear representation of a protein, the left end typically represents the beginning of the amino acid chain, while the right end represents the end of the chain.

3. **Amino Acid Structure**:
- Each amino acid has two important functional groups: an amino group (-NH2) and a carboxyl group (-COOH). The amino group is found at one end of the amino acid, while the carboxyl group is at the other end.

4. **Determining the Left End**:
- Since the left end of the protein chain corresponds to the first amino acid in the sequence, it will have its amino group exposed. Therefore, the left end represents the first amino acid and its amino terminal.

5. **Conclusion**:
- Based on the above understanding, the left end of the primary structure of a protein represents the first amino acid and its amino terminal.

### Final Answer:
The left end represents the first amino acid and its amino terminal.