The first amino acid in peptide chain is also called____

Answer

To answer the question "The first amino acid in a peptide chain is also called____", we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Amino Acids**:
- Amino acids are the building blocks of proteins. Each amino acid has a central carbon atom bonded to four groups: an amino group, a carboxyl group, a hydrogen atom, and a variable side chain (R group).

2. **Identifying the Peptide Chain**:
- A peptide chain is formed when amino acids are linked together through peptide bonds. The sequence of amino acids in a peptide chain determines the structure and function of the protein.

3. **Recognizing the First Amino Acid**:
- The first amino acid in a peptide chain is determined during the process of translation, where the ribosome synthesizes proteins based on the mRNA sequence.

4. **Role of Start Codon**:
- The translation process begins at a specific sequence in the mRNA known as the start codon. The start codon is typically AUG, which codes for the amino acid methionine.

5. **Naming the First Amino Acid**:
- Since methionine is coded by the start codon (AUG), it is the first amino acid incorporated into the peptide chain. Additionally, the position of this amino acid is referred to as the N-terminus of the peptide chain.

6. **Final Answer**:
- Therefore, the first amino acid in a peptide chain is also called the **N-terminal amino acid** or **methionine**.

### Summary:
The first amino acid in a peptide chain is known as the **N-terminal amino acid** or **methionine**.

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