In biochemistry, denaturation is a process in which proteins or nucleic acids lose the quaternary structure, tertiary structure, and secondary structure which is present in their native state, by application of some external stress or compound, such as a strong acid or base, a concentrated inorganic salt, an organic solvent (e.g., alcohol or chloroform), agitation and radiation, or heat. If proteins in a living cell are denatured, this results in disruption of cell activity and possibly cell death. Protein denaturation is also a consequence of cell death. Denatured proteins can exhibit a wide range of characteristics, from conformational change and loss of solubility or dissociation of cofactors to aggregation due to the exposure of hydrophobic groups. The loss of solubility as a result of denaturation is called coagulation. Denatured proteins lose their 3D structure, and therefore, cannot function.
Proper protein folding is key to whether a globular or membrane protein can do its job correctly; it must be folded into the native shape to function. However, hydrogen bonds and cofactor-protein binding, which play a crucial role in folding, are rather weak, and thus, easily affected by heat, acidity, varying salt concentrations, chelating agents, and other stressors which can denature the protein. This is one reason why cellular homeostasis is physiologically necessary in most life forms.
This concept is unrelated to denatured alcohol, which is alcohol that has been mixed with additives to make it unsuitable for human consumption.