Probably the most important effect of temperature is on the shapes of
enzymes required for metabolism. I'm sure you aware that bacteria can
be classified based on their optimal growth temperatures. When a
mesophile, for instance, is placed a 4oC, growth almost completely
stops. This is due to the fact that enzyme shapes are very dependent
on temperature, and enzyme activity is dependent on the enzyme's
shape. Enzymes will have the proper shape only within a relatively
narrow range of temperatures.