Final answer:
Hydrogen bonds in a β-sheet occur between the carbonyl oxygen and amine hydrogen atoms in the backbone of the polypeptide chain across adjacent spans. The correct answer is D. adjacent spans.
Step-by-step explanation:
In a β-sheet, hydrogen bonds form between the backbone atoms on different strands of the sheet. Specifically, the bonds occur between the carbonyl oxygen atom (C=O) of one amino acid and the amine hydrogen (N-H) of another. This interaction takes place between the peptide bonds that link individual amino acids together; it does not typically involve the side chains (R groups) of the amino acids, although the nature of the side chains can influence the overall folding and shape of the protein.
The correct answer to the question "In a β-sheet, hydrogen bonds form between which of the following?" is D. adjacent spans of the peptide backbone, not the amino acid side chains or the termini of the protein. The side chains protrude above and below the folds of the pleat and do not generally participate in the hydrogen bonding that defines the β-sheet structure.
In a β sheet, hydrogen bonds form between adjacent spans. The β sheet structure is formed when polypeptide chains lie side by side, and hydrogen bonds form between the carbonyl oxygen of one peptide bond and the amino hydrogen of an adjacent peptide bond. These hydrogen bonds stabilize the structure of the β sheet.