Quick questions on Enzymes and factors affecting activity (SACE Stage 2 Biology)

As temperature rises, molecules move faster and collide more often, so the reaction rate increases up to an optimum temperature (around 37 degrees Celsius for many human enzymes). Above the optimum, heat breaks the bonds maintaining the enzyme's tertiary structure, so the enzyme denatures, the active site changes shape, and activity falls sharply.

Each enzyme has an optimum pH at which its active site is the correct shape. For example, pepsin in the stomach works best around pH 2, while many cellular enzymes prefer about pH 7. Moving away from the optimum disrupts ionic and hydrogen bonds, changing the active site and reducing activity; extreme pH denatures the enzyme.

Increasing substrate concentration increases the reaction rate because more substrate molecules collide with active sites. Eventually all active sites are occupied (saturation), so the rate levels off at a maximum; adding more substrate then has no effect.

If substrate is plentiful, increasing enzyme concentration increases the rate because more active sites are available to bind substrate.

Inhibitors reduce enzyme activity. Competitive inhibitors resemble the substrate and bind to the active site, blocking it; their effect can be reduced by adding more substrate. Non-competitive inhibitors bind elsewhere on the enzyme, changing the active site's shape so the substrate no longer fits.