In biochemistry, denaturation is the process by which proteins or nucleic acids lose their native quaternary, tertiary, and/or secondary structure. Denaturation can be caused by conditions such as strong acid or base, concentrated salt, organic solvents, or heat. Protein denaturation generally results in the loss of enzymatic activity. Denatured proteins may become insoluble or aggregate. Nucleic acid denaturation results in the separation of hydrogen-bonded complementary regions when the hydrogen bonds between the strands are broken. These bonds may be restored by annealing. Denaturation typically does not result in the breaking of the covalent bonds which hold a polymer together. Denaturation is often reversible in proteins and nucleic acids.