In the molecule of a peptide, the amino acid residue on one end has an amine group on the alpha carbon.  This amino acid residue is called the N-terminal of the peptide.  The amino acid residue on the other end has a carboxylic acid group on the alpha carbon.  This amino acid is called the C-terminal.


When the structure of a peptide is drawn horizontally, by convention, the N-terminal is placed on the left and the C-terminal on the right.

The convention is important because the amino acid sequence of peptides is often shown using the symbols of the constituent amino acids.


The above peptide molecules have the same number of amino acid residues (3) and the same amino residues (alanine, cysteine, and valine), but they represent two different peptides.

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