What happens to enzymes when the temperature exceeds their optimum level?

When the temperature exceeds the optimum level for enzyme activity, the primary effect is denaturation. This process involves the unfolding and structural disruption of the enzyme's three-dimensional shape, which is critical for its function. Enzymes are made up of proteins, and their activity is highly dependent on their specific structural conformation. High temperatures increase the kinetic energy of the enzyme and substrate molecules, which can initially enhance the reaction rate up to a point. However, as the temperature continues to rise beyond the optimal level, the bonds that maintain the enzyme's structure (like hydrogen bonds and hydrophobic interactions) begin to break.

Once denaturation occurs, the active site of the enzyme, which is where substrate binding and catalysis take place, is altered or destroyed. This alteration often leads to a loss of enzymatic function, meaning that the enzyme can no longer facilitate the biochemical reaction it was responsible for. This is why the option stating that they denature and stop functioning is the correct choice. The other options suggest inappropriate consequences related to enzyme behavior under high temperatures, such as increased efficiency, rapid multiplication, or excess energy release, which do not align with the biological principles governing enzyme dynamics.