Enzymes are biological catalysts. They speed up chemical reactions in all living things, and allow them to occur more easily.
They occur in plant cells and animal cells. Without them we would not be alive.
Although they work powerfully, enzymes are just chemical molecules, made up of proteins. They are too small to be seen either when they are inside cells or after they have been released from them, for example in the digestive system.
Each particular enzyme has a unique, 3-dimensional shape shared by all its molecules. Within this shape there is an area called the active site where the chemical reactions occur.
What do enzymes do?
Some enzymes help to break down large molecules. Others build up large molecules from small ones. While many others help turn one molecule into another.
Probably the fastest enzyme known is called catalase.
It breaks the chemical hydrogen peroxide down to water and oxygen. Catalase is found in all cells and protects them from this dangerous waste chemical.
The substrate (hydrogen peroxide) and the catalase molecules are continuously on the move. Every so often they will collide so that the substrate molecule(s) fits into the enzyme's active site.
Then the substrate is broken down into the…