Peptide Naming from Amino Acid Sequence

Peptides are named based on the sequence of amino acid residues they contain. The nomenclature follows specific rules:

• The N-terminal amino acid (at the beginning of the chain) is usually named first.
• Amino acid residues within the peptide chain (internal residues) typically have their suffix changed to -yl (e.g., aspartate becomes aspartyl, glutamate becomes glutamyl).
• The C-terminal amino acid (at the end of the chain) retains its full name.

Applying Naming Rules

Given sequence: Cysteine-aspartate-glutamate-alanine

1. Cysteine (N-terminus): In many contexts, the N-terminal amino acid keeps its full name. However, based on the provided options, the "-yl" suffix is used, leading to Cysteinyl.
2. Aspartate (Internal): This residue becomes Aspartyl.
3. Glutamate (Internal): This residue becomes Glutamyl.
4. Alanine (C-terminus): This is the final amino acid, so it keeps its full name: Alanine.

Final Peptide Name

Combining these, the peptide is named: Cysteinyl-aspartyl-glutamyl-alanine.