what are enzymes?

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. Enzymes are 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.