What best describes a peptide?

• A. A small protein
• B. A protein chain of a single amino acid.
• C. A protein containing essential amino acids
• D. A molecule containing a protein and a lipid

Answer: (A)

A peptide is a short chain of amino acids linked by peptide bonds. Because it is shorter than a full-length protein, it’s often described as a small protein or a fragment of a protein. This captures the idea that peptides are proteins in form but at a smaller, simpler scale.

The other ideas don’t fit as well: a peptide is not just a single amino acid in length, so a chain of a single amino acid is incorrect; a peptide isn’t defined by containing essential amino acids specifically, and it isn’t a molecule that combines protein with a lipid—lipids interact with proteins in other contexts, not what defines a peptide.