This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
[{'content': 'The primary structure of a protein refers to \nSelect and explain. \nA. Linear structure and order of the amino acids present, B. Regular confirmational forms of a protein, C. Complete three-dimensional structure of the polypeptide units of a given protein, D. Subunit structure of the protein', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The linear sequence of amino acid residues and location of disulphide bridges, if any, in a polypeptide constitute its primary structure.', 'role': 'assistant'}]