How does pH and temperature effect an enzyme-catalyzed reaction?

It depends on the exact structure of the protein (aka the enzyme). Each enzyme will have a preferred pH and temperature under which is till be working best. You should also know though that too high a temperature will be detrimental to almost all enzymes as it will cause denaturing of the protein and thus loss of function. The best approach for your essay might be to pick one or two enzymes whose catalytic function are easily observable experimentally and then describe experiments in which you very the temperature and pH and measure a change in catalytic activity (which u can determine based on the amount produced). Information on how individual enzymes based on their structure react to the change should be found in most Biochemistry textbooks.

Hope this helps to get you started!

pH can affect the ionization of the amino acid side chain, which in turn change the secondary, tertiary and quaternary structures of the protein molecule. This will change the enzyme's active site and consequently its activity.