Which of the following statements concerning protein structure is incorrect?

• A. Primary structure refers to the sequence of amino acids in a protein.
• B. Secondary structure is stabilized by hydrogen bonds between the backbone atoms.
• C. Tertiary structure is determined by interactions between R groups of amino acids.
• D. Quaternary structure is the linear sequence of amino acids in a polypeptide chain.

Answer: (D)

Verified step by step guidance

1. Understand the four levels of protein structure: primary, secondary, tertiary, and quaternary.
2. Primary structure is the linear sequence of amino acids in a protein, held together by peptide bonds.
3. Secondary structure refers to local folded structures that form within a polypeptide due to interactions between atoms of the backbone. The most common types are alpha helices and beta sheets, stabilized by hydrogen bonds.
4. Tertiary structure is the overall three-dimensional shape of a single protein molecule, formed by interactions between the R groups (side chains) of the amino acids, including hydrogen bonds, ionic bonds, disulfide bridges, and hydrophobic interactions.
5. Quaternary structure involves the assembly of multiple polypeptide chains into a functional protein complex. It is not about the linear sequence of amino acids, but rather the arrangement and interaction of multiple subunits.