Enzymes have a specific shape that allows them to bind to a specific substrate at the active site. They speed up chemical reactions by lowering the activation energy needed. An enzyme's activity is affected by temperature, pH, and substrate concentration. Temperature and pH can cause an enzyme to denature and lose its shape and function. The reaction rate increases with temperature until the enzyme denatures. Enzymes work most efficiently at an optimal pH and substrate concentration, beyond which there is no additional effect. Lactose in milk is broken down by the enzyme lactase into glucose and galactose, but some people lack this enzyme, causing lactose intolerance.

1. 3.6 enzymes
Enzymes have specific shape and it need specific enzyme substrate to match the active site.
They are specific to each other.
Active substrate: the binding site on the surface of an enzyme where the substrate molecule
binds.
Enzyme influences the rate of reaction. It lowers the activation energy of reaction.
There are three main factors which affecting enzyme-catalyses reaction.
1. Effect of temperature
Reaction with or without enzymes will increase their reaction rate as temperature
increase.
Those enzyme used in reaction have an upper limit.
When an enzyme loses its shape, it’s being denatured.
Denaturation is changing the structure of an enzyme so it can no longer carry out its
function.
2. Effect of pH
Enzymes usually have an optimum pH at which they work most efficiently. As the pH
diverges from the optimum, enzyme activity decreases. Both acid and alkali
environments can denature enzymes.
3. Effect of concentration
If there is constant amount of enzyme, as the concentration of a substrate increases, the
rate of reaction will increase as well.
At the optimum concentration of substrate molecules, all active sites are full and
working at maximum efficiency.
Any increase in concentration beyond the optimum will have no added effect as there
are no extra active sited to be used.
Lactose is the sugar found in milk. It can be broken down by enzyme lactase to glucose and
galactose. However some people lack this enzyme and so cannot break down lactose leading to
lactose intolerance. Lactose intolerant people need to drink milk that has been lactose reduced.
Lactose-free milk is made by two different methods: add lactase to milk and run milk through
apparatus with immobilized lactase.