Final answer:
A tetrapeptide, which has three peptide bonds, contains four amino acids. Peptide bonds connect amino acids in a chain, where each bond involves a link between two amino acids and the chain always has two free ends.
Step-by-step explanation:
If a tetrapeptide has 3 peptide bonds, it contains four amino acids. Peptide bonds are the chemical bonds that connect amino acids together in a polypeptide chain, and each bond is between two amino acids. Starting from a single amino acid (a monopeptide), when a second amino acid is added, one peptide bond is formed, creating a dipeptide. Adding a third amino acid creates a second bond (a tripeptide) and adding a fourth amino acid creates the third bond, which results in a tetrapeptide.
It is similar to adding links to a chain; each new link requires one connection point, but the two ends of the chain always remain as they were from the beginning (with the N-terminal end having a free amino group and the C-terminal end having a free carboxyl group). Therefore, a tetrapeptide will always have one more amino acid than the number of peptide bonds.