AAMC FL Practice Exam

What structure in proteins is formed by hydrogen bonds between the backbone of amino acids?

1. Primary structure

2. Secondary structure

3. Tertiary structure

4. Quaternary structure

The correct answer is: Secondary structure

The secondary structure of proteins is formed by hydrogen bonds that occur between the backbone atoms of amino acids. This structure refers to the localized folding of the polypeptide chain into structures such as alpha helices and beta sheets. The hydrogen bonds typically form between the carbonyl oxygen of one amino acid and the amide hydrogen of another, stabilizing these common motifs and contributing to the overall architecture of the protein. In contrast, the primary structure pertains to the unique sequence of amino acids in the polypeptide chain, which is determined by the genetic code and does not involve any folding or interactions. The tertiary structure refers to the overall three-dimensional shape of a single polypeptide chain that results from interactions among the side chains (R groups) of the amino acids, which may involve various types of bonding, including hydrogen bonds, but also ionic and hydrophobic interactions. The quaternary structure involves the assembly of multiple polypeptide chains into a larger complex, which can also be stabilized by hydrogen bonds, but this is distinct from the interactions that define the secondary structure. Thus, the correct answer accurately identifies the secondary structure as the arrangement that arises specifically due to hydrogen bonding between the backbone elements of amino acids.