2.7—Enzyme action and specificity

An enzyme is a globular protein whose tertiary structure creates a specific active site. A substrate binds by complementary shape and chemical interactions, forming an enzyme–substrate complex that lowers activation energy.

The induced-fit idea explains why binding can alter the active site slightly and position reactants for reaction. Temperature, pH and inhibitors can change the active site or block it, changing rate without changing the substrate itself.

If an enzyme’s active site loses its shape at extreme pH, the substrate concentration may remain high but fewer productive complexes form. A competitive inhibitor lowers the chance that substrate occupies the site.

Explain a rate change through collision frequency, active-site occupancy and protein structure. Distinguish denaturation from reversible inhibition when the conditions allow recovery.

The “lock and key” picture is a useful starting model, not a claim that the enzyme is rigid. Specificity does not mean an enzyme works at only one temperature or pH.