Final answer:
The first amino acid in a synthesized polypeptide is at the N-terminal end, usually methionine, which is removed after synthesis as protein grows from the N-terminal to the C-terminal end.
Step-by-step explanation:
When a polypeptide is synthesized, the first amino acid to be put in place is located at the N-terminal end. The amino acid methionine, coded by the codon AUG which also serves as the initiation codon, is the first amino acid incorporated into each newly synthesized polypeptide. However, this initial methionine is typically removed before the polypeptide chain is fully synthesized, meaning that the vast majority of mature polypeptides do not start with methionine after undergoing post-translational modifications.
Proteins and polypeptides grow from the amino (N-) terminal end to the carboxyl (C-) terminal end. Sanger's, Edmann's, and Dansyl chloride reagents are used to identify the N-terminal amino acids, while hydrazine is used for the C-terminal amino acids. After synthesis, the polypeptide chain may fold and undergo further modifications to become a functionally active protein.