An enzyme is a globular protein functioning as a biological catalyst. An active site is the place on the surface of an enzyme to which substrate or substrates bind.

3.6.2 Explain enzyme–substrate specificity.
The active site has a particular three-dimensional structure that corresponds to a specific substrate rather like a lock and key.
3.6.3 Explain the effects of temperature, pH and substrate concentration on enzyme activity. For all enzymes, there is an optimum temperature at which the maximum amount of collisions occur in the active sites. As the temperature decreases, there is less movement and fewer collisions, so enzyme activity decreases. There is a limit to which the enzyme activity can increase because at a certain temperature the active site is distorted by heat
Enzyme activity increases with substrate concentration but only up to a certain point. There is an upper limit to the increase in enzyme activity because at some point all available active sites are filled.
Enzymes are pH sensitive. Hydrogen ions can interfere with hydrogen bonding and, in extreme cases, may even break covalent bonds. There is an optimal pH level for each enzyme. 3.6.4 Define denaturation.
Denaturation is a structural change in a protein that results in the loss (usually permanent of its biological properties. Refer only to heat and pH as agents
3.6.5 Explain the use of lactase in the production of lactose-free milk.
Production of lactose-free milk is an example of an industrial process depending on biological methods (biotechnology). Lactose intolerance is found in a high proportion of the human population (for example, in Asia) but more rarely among those of European origin.
Lactose-free milk is produced industrially by passing milk over lactase enzyme bound to an inert carrier (alginate beads). The enzyme cleaves the lactose disaccharide into glucose