Denaturation

Proteins denature when they lose their three-dimensional structure and thus their characteristic folded structure. Enzymes lose their catalytic activity, because the substrates cannot bind to the active site any more. Some, but not all, proteins can regain their correct structure when the denaturing influence is removed.

The denaturation of nucleic acids such as DNA, also called melting, is the separation of a double strand into two single strands, which occurs when the hydrogen bonds between the strands are broken. Nucleic acid strands realign when "normal" conditions are restored.