Which of the following determines the primary structure of a protein?

• A. The arrangement of alpha helices and beta sheets
• B. The association of multiple polypeptide chains
• C. The overall three-dimensional shape of the protein
• D. The sequence of amino acids linked by peptide bonds

Answer: (D)

Verified step by step guidance

1. Understand the concept of protein structure: Proteins have four levels of structure—primary, secondary, tertiary, and quaternary. The primary structure refers to the linear sequence of amino acids in a polypeptide chain, linked by peptide bonds.
2. Recognize that peptide bonds are covalent bonds formed between the carboxyl group of one amino acid and the amino group of another during protein synthesis.
3. Differentiate the primary structure from other levels: Secondary structure involves local folding patterns like alpha helices and beta sheets, tertiary structure refers to the overall 3D shape, and quaternary structure involves the interaction of multiple polypeptide chains.
4. Identify that the sequence of amino acids in the primary structure is determined by the genetic code in the DNA, which is transcribed into mRNA and translated during protein synthesis.
5. Conclude that the primary structure is the foundation for all higher levels of protein structure, as the sequence of amino acids dictates how the protein will fold and function.