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

• A. The three-dimensional arrangement of protein subunits
• B. The linear sequence of amino acids in a chain
• C. The folding and coiling of a polypeptide
• D. The overall shape formed by multiple polypeptides

Answer: (B)

The primary structure of a protein is defined as the linear sequence of amino acids in a polypeptide chain. This sequence is crucial because it dictates the subsequent folding and three-dimensional structure of the protein, which directly influences its function. The specific order of amino acids is encoded by the genetic information in DNA, and any changes in this sequence (such as mutations) can lead to alterations in protein function, potentially resulting in diseases.

Each amino acid in the primary structure is linked to the next by peptide bonds, forming a long chain. This chain can then undergo various types of folding and coiling to achieve higher-order structures, but it is the primary sequence that ultimately determines how the molecule will assume these complex shapes. Understanding the primary structure is essential for exploring how proteins work and how their structures relate to their biological functions.