Enzymes are a group of proteins. Enzymes control the chemical reactions that take place in a cell. Enzymes are biological catalysts. A catalyst is a chemical which speeds up a reaction without being used itself, it takes part in a reaction but is unchanged and can catalyst more reactions. Cells contain hundreds of different enzymes, each enzyme catalys a different reaction. Everything a cell does depends on which enzyme it can make, which in turn depends on which genes in nucleus are working.
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