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
Protein structure not lost in denaturation is ? 
Select and explain. 
A. Primary structure, B. Secondary structure, C. Teiary structure, D. Quaternary structure
A: Primary structure
Answer: A: Primary structure 
Explanation: Ans. is 'a' i.e., Primary structure The term denaturation refers to disruption of higher order (secondary, teiary and quaternary) structure of protein.All non-covalent bonds that maintain higher order structure are disrupted, but peptide bond (covalent bond) remains intact. Thus, the primary structure is not altered during denaturation, i.e., amino acid sequence is not altered, but denaturation may completely disrupt secondary, teiary and quaternary structure, e.g., denaturated oligomeric proteins dissociated into subunits, each with a randam coil formation.Denaturation is always accompanied by a loss of biological function, e.g., enzymes are inactivated and antibodies fail to act with antigens.Denaturation is generally irreversible, e.g., boiled egg does not regain its original form when kept in cold.Denatured proteins are less soluble and in many cases they precipitate.