Which of the following is the best practical reason, based on the lesson, to classify a polypeptide with 40 amino acids differently than a protein with 400 amino acids?

• A. A 40-residue chain is often considered a peptide due to its small size and different folding/functional properties, whereas 400 residues fall well within the typical protein size range and usually has more complex structure and functions.
• B. Only chains longer than 10,000 residues can be considered proteins; anything smaller is non-functional and nutritionally irrelevant.
• C. There is no conceptual distinction; any chain with more than one amino acid is always classified as a protein regardless of length or function.
• D. A 40-residue chain is automatically more nutritionally valuable than a 400-residue protein because shorter chains supply more nitrogen per gram.

Answer: (A)