What type of bond joins amino acids in a polypeptide chain?

The correct answer is the type of bond known as peptide bonds. Peptide bonds specifically form between the amino group of one amino acid and the carboxyl group of another amino acid, with the release of a molecule of water (a process known as dehydration synthesis). This covalent bond is critical for linking amino acids together to form polypeptides and ultimately proteins, which are essential for countless biological functions.

While hydrogen bonds play important roles in stabilizing the three-dimensional structure of proteins by forming interactions between different parts of the polypeptide chain, they do not directly link amino acids together in a polypeptide. It is also important to note that although peptide bonds are indeed a type of covalent bond, the term "peptide bond" specifically refers to the covalent connection formed during the synthesis of proteins, thereby distinguishing it from other covalent bonds that might not involve amino acids. Finally, ionic bonds typically involve attractions between charged groups and do not form the backbone structure of polypeptides.