Denaturation

In the syllabus and the exam

Denaturation is tested mainly through enzyme-rate graphs, where candidates must explain the sharp drop in reaction rate once temperature rises above the enzyme's optimum, or once pH moves too far from the optimum in either direction, attributing this drop specifically to the permanent change in the enzyme's, and particularly its active site's, three-dimensional shape. A precise answer distinguishes denaturation from simply 'slowing down': below the optimum temperature, an enzyme's rate decreases because particles move more slowly and collide less often, and this effect is reversible once the temperature rises again; above the optimum, however, the enzyme is denatured, its shape is permanently changed, and raising the temperature further will not restore its activity. A common error is stating that an enzyme is 'denatured' at low temperatures, or that a denatured enzyme can become active again once conditions return to normal, both of which are factually incorrect and heavily tested misconceptions in this chapter. Candidates should also be able to link denaturation back to protein structure, explaining that because enzymes are proteins made of a specific folded arrangement of amino acids, extreme heat or extreme pH disrupts the bonds holding this folded shape together, and once that shape is lost, the substrate can no longer fit into the active site. Candidates are also expected to know that not all proteins denature at the same temperature, and that this variation is exploited in food preservation and cooking, where controlled heating is used deliberately to denature enzymes in fruit and vegetables and stop them from continuing to ripen or spoil.

Example

Boiling an egg denatures the proteins in the egg white, permanently changing their shape from a clear liquid to a solid white mass that cannot return to its original form.

Related terms

EnzymeActive site

Source:SRC-DSKP-EN