Enzymes are biological catalysts.
Enzymes are also proteins, that are folded into complex shapes that allow smaller molecules to fit into them. The place where these substrate molecules fit is called the active site.
Enzymes usually denatured above about 45ºC. They can be denatured by high temperatures or extremes of pH.
Enzymes in cells catalyse photosynthesis, protein synthesis - joining amino acids together, and aerobic respiration
The main enzymes are; Lipase, (produced in pancreas + small intestine) Amylase (produced in salivary glands, pancreas, small intestine), and Protease (produced in stomach, pancreas + small intestine).
Lipase converts fat into fatty acids and glycerol
Amylase converts Starch into glucose and simple sugars
Protease converts proteins into amino acids.