This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Structure and function of protein, Subject name: Biochemistry
[{'content': 'Proteins are linear polymers of amino acids. They fold into compact structures. Sometimes, these folded structures associate to form homo or hetero-dimers. Which of the following refers to this associated form? \nSelect and explain. \nA. Denatured state, B. Molecular aggregation, C. Precipitation, D. Quaternary structure', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Quaternary structure defines the polypeptide composition of a protein and, for an oligomeric protein, the spatial relationships between its protomers or subunits. Monomeric proteins consist of a single polypeptide chain. Dimeric proteins contain two polypeptide chains. Homodimers contain two copies of the same polypeptide chain, while in a heterodimer the polypeptides differ. Ref: Harper 28th Ed. Page-35, Harper 27th Ed. Page: 34', 'role': 'assistant'}]