Which of the following best describes the primary structure of a protein?

• A. The linear sequence of amino acids joined by peptide bonds
• B. The overall three-dimensional shape of a single polypeptide chain
• C. The association of multiple polypeptide subunits into a functional protein complex
• D. The folding of the polypeptide chain into alpha-helices and beta-sheets

Answer: (A)

Verified step by step guidance

1. Understand the concept of protein structure: Proteins have four levels of structure—primary, secondary, tertiary, and quaternary. Each level describes a different aspect of the protein's organization.
2. Define the primary structure: The primary structure refers to the linear sequence of amino acids in a polypeptide chain, connected by peptide bonds. This sequence is determined by the genetic code.
3. Differentiate the primary structure from other levels: Secondary structure involves local folding into alpha-helices and beta-sheets, tertiary structure describes the overall three-dimensional shape of a single polypeptide chain, and quaternary structure refers to the association of multiple polypeptide subunits.
4. Match the description to the correct definition: The primary structure is best described as 'The linear sequence of amino acids joined by peptide bonds.'
5. Review the importance of primary structure: The sequence of amino acids in the primary structure determines how the protein will fold and function, making it a critical aspect of protein biochemistry.