Proteins denature under certain conditions and denaturation primarily alters which level of structure?

• A. Primary structure
• B. Secondary structure
• C. Tertiary structure
• D. Quaternary structure

Answer: (C)

Denaturation disrupts the protein’s three-dimensional arrangement while leaving the amino acid sequence intact. The primary structure stays the same because peptide bonds lock the sequence together, but the interactions that give the chain its folded shape—hydrogen bonds, ionic interactions, hydrophobic effects, and any disulfide bonds—are broken or weakened. This causes the protein to unfold and lose its specific, functional shape, which is the essence of the tertiary structure. Secondary structures like helices and sheets are affected as part of this unfolding, but the defining change is the loss of the overall three-dimensional fold that defines the tertiary structure.