Describe how the tertiary protein structure relates to enzyme function.

Explain the control of metabolic pathways by end-product inhibition, including the role of allosteric sites.

tertiary is the specific 3D structure (determined by the primary structure);
giving rise to the specific shape of the active site;
(tertiary structure) enables enzymes to bind (effectively) to substrate;
determines whether some enzymes have broad or narrow specificity;
inhibitors/cofactors can affect tertiary structure and therefore function;

inhibitor is the product of the last reaction in a metabolic pathway;
inhibits the enzyme that catalyses the first reaction;
prevents build up of unnecessary product/only produced when needed;
the inhibitor binds (reversibly) to the allosteric site (different from active site);
this alters the shape of active site (so substrate will not fit);
To award [3] answers must mention allosteric sites.

Candidates had difficulty describing the relationship between protein structure and enzyme function in (a) although many had a general idea of it but not enough to score marks.

(b) Some good responses by strong candidates were awarded the full 3 marks, showing a good understanding of end-product inhibition and allosteric sites.