Quick questions on Factors affecting enzyme activity: H2 Biology Energy and Equilibrium

As temperature rises, molecules gain kinetic energy, collide more often and with more energy, and form more enzyme-substrate complexes, so the rate rises to an optimum. Above the optimum the rate falls sharply because the enzyme denatures: increased vibration breaks the hydrogen and ionic bonds of the tertiary structure, the active site changes shape, and the substrate no longer fits.

Each enzyme has an optimum pH at which its active site shape is ideal. Moving away from the optimum alters the charges on the R groups of the active site, disrupting the ionic and hydrogen bonds that hold its shape. The active site changes, the substrate binds less well, and the rate falls. Extremes of pH denature the enzyme.

At low substrate concentration the rate rises with concentration because more substrate is available to bind. The rate then plateaus because the active sites become saturated: nearly all are occupied at any moment, so adding more substrate cannot help, and enzyme concentration becomes limiting.

Provided substrate is in excess, increasing the enzyme concentration increases the rate proportionally, because there are more active sites available to form complexes. If substrate is limited, the rate eventually plateaus when the substrate runs short.

State what happens to an enzyme at a temperature well above its optimum. [1 mark]

Explain why the rate of an enzyme reaction is low at a pH far from the enzyme's optimum. [2 marks]

A reaction has reached its plateau on a substrate-concentration graph. State what must be done to increase the rate further. [1 mark]