In the primary structure of protein

Options

A. Left end represents `rarr` 1 st amino acid (C- terminal amino acid)
B. Right end represents `rarr` Last amino acid (N -terminal amino acid)
C. Left end represents `rarr` 1 st amino acid (N- terminal amino acid)
D. Right end represents `rarr` Last amino acid (C- terminal amino acid)

Answer

**Step-by-Step Solution:**

1. **Understanding the Primary Structure of Proteins:**
- The primary structure of a protein refers to the linear sequence of amino acids linked together by peptide bonds. This sequence is determined by the genetic code.

2. **Identifying Key Components:**
- Each amino acid has a central carbon atom (Cα) to which four groups are attached:
- An amino group (NH2) on the left side.
- A carboxyl group (COOH) on the right side.
- A hydrogen atom.
- An R group (side chain) that varies between different amino acids.

3. **Defining N-terminal and C-terminal:**
- The end of the amino acid chain with the amino group (NH2) is called the N-terminal (or amino terminus).
- The end of the chain with the carboxyl group (COOH) is called the C-terminal (or carboxyl terminus).

4. **Analyzing the Statements:**
- The first statement claims that the left end represents the first amino acid. This is correct; the left end (N-terminal) is where the first amino acid is located.
- The second statement claims that the right end represents the last amino acid. This is incorrect; the right end is the C-terminal, which does not represent an amino acid but rather the end of the chain.
- The third statement reiterates that the left end represents the first amino acid, which is correct.

5. **Conclusion:**
- The correct understanding is that the left end (N-terminal) represents the first amino acid, while the right end (C-terminal) signifies the end of the amino acid chain, not necessarily the last amino acid itself.

**Final Answer:**
- The left end represents the first amino acid (N-terminal), and the right end represents the C-terminal.

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