Final answer:
Peptide bonds are responsible for holding adjacent amino acids together in a polypeptide chain, resulting from a dehydration synthesis reaction.
Step-by-step explanation:
Adjacent amino acids in a polypeptide chain are held together by peptide bonds. Peptide bonds are a type of covalent bond formed through a dehydration synthesis reaction. This occurs when the carboxyl group of one amino acid reacts with the amino group of another, releasing a water molecule and creating the bond.
Long chains of amino acids that form as a result are known as polypeptides or proteins, and their sequence and number are critical for determining the protein's characteristics such as shape, size, and function.