Enzymes and investigations, at a glance

An enzyme provides a lower-activation-energy route; it does not change the reactants, products or overall energy difference.

• Lower activation energy, unchanged overall energy difference.
• Enzyme-substrate complex forms temporarily.
• Induced fit includes conformational change.

Keep in mind: It lowers the activation barrier through a different reaction pathway.

Temperature affects collision frequency and stability; pH affects binding-site charges and protein interactions.

• Warmer: faster collisions until stability is lost.
• pH can alter charge and binding.
• An optimum depends on assay conditions.

Keep in mind: Rate can fall because of lower temperature, limited substrate or altered ionisation without complete denaturation.

At high substrate concentration, occupied active sites limit rate; measure initial slopes or a justified reciprocal-time proxy.

• Substrate plateau: enzyme capacity limits rate.
• More enzyme helps only while substrate is sufficient.
• Initial slope and 1/time are different rate measures.

Keep in mind: Substrates still move; enzyme availability and turnover limit further increases in rate.

A competitive inhibitor competes at the active site; a non-competitive model reduces functional catalytic capacity through another binding site.

• Competitive: active-site competition.
• More substrate can overcome reversible competitive inhibition.
• Non-competitive capacity loss lowers the plateau in the simple model.

Keep in mind: Many inhibitors bind reversibly, and different binding mechanisms produce different kinetic effects.