Where does denaturation collide?

The disruption of a protein's native three-dimensional structure, its working folded shape, by heat, extremes of acidity, or chemical agents, so that it loses the biological activity that depended on that shape while its underlying chain of amino acids stays intact. Anfinsen's 1973 Principles that Govern the Folding of Protein Chains, drawing on experiments that unfolded and refolded the enzyme ribonuclease, showed that the folded structure is written into the amino-acid order itself, so denaturation and its reversal became a window onto how proteins fold. The referent is the collapse of one molecule's working shape, measured on single proteins in solution, not the splitting of a paired DNA strand or the poisoning of drinking alcohol.[1]

Unit

One protein losing its native folded shape and activity

Recovery means

Sometimes reversible: a small protein can refold to its native shape once the denaturing condition is removed

Measured by

Followed by loss of activity and by spectroscopy or calorimetry that tracks unfolding as heat or chemical conditions change

The unwinding and separation of the two strands of the DNA double helix into single strands as heat or chemicals break the weak bonds pairing the bases, summarised by a melting temperature, the point at which half the sample has come apart. Marmur and Doty's 1962 Determination of the base composition of deoxyribonucleic acid from its thermal denaturation temperature showed that this melting temperature rises with the fraction of guanine-cytosine pairs, giving a clean measured quantity, and the same strand separation later became a working step in copying and detecting DNA. The referent is the coming-apart of a paired double strand, indexed by a melting temperature, not the unfolding of a single protein or the adulteration of alcohol.[2]

Unit

A DNA double helix separating into two single strands

Recovery means

Reversible: cooled slowly, complementary strands re-pair (anneal) back into a double helix

Measured by

Tracked by the rise in ultraviolet absorbance on melting and summarised as the melting temperature, Tm