5.1 Enzymes

If the catalyst is present before and after the reaction while the substrate decreases and products increase, it has sped up the conversion without becoming a product.

Metabolism is the set of chemical reactions in cells and organisms. Enzymes control reactions in processes such as digestion, respiration and the building or breakdown of molecules.

Without enzymes, many necessary reactions would be too slow under normal biological conditions. Raising body temperature enough to speed them chemically would damage cells, so biological catalysts are essential.

Complementary means the shapes fit one another; it does not mean they are identical shapes. The substrate occupies the active site because their outlines match.

Use a range of values, allow solutions to reach the target condition before mixing, start timing on mixing, repeat, calculate mean rates and plot rate against temperature or pH.

The optimum is the condition giving the highest rate—or shortest time to a fixed endpoint. Above the temperature optimum, activity falls sharply as enzymes denature.

enzyme + substrate → enzyme–substrate complex → enzyme + product(s)

The active site becomes free after products leave, so the same enzyme molecule can catalyse another reaction.

Different substrates have different shapes, so organisms require different enzymes for different reactions.

Specificity depends on the three-dimensional fit at the active site, not on the whole enzyme and substrate having the same outline.

The rise is gradual because collision frequency increases progressively; the fall can be steep because denaturation removes correctly shaped active sites.

Different enzymes can have different optimum pH values because they work in different environments and have different protein structures.

Describe a pH graph using its active range, optimum pH and changes on both sides, then explain the changes through active-site shape, fit and denaturation.