Structure of enzymes
Enzymes are proteins that alter the rate of chemical reactions without themselves chemically changed at the end of the reaction.
Lock and Key Hypothesis of enzymes
An enzyme is the 'lock' which has an unique shape that binds to a specific substrate that serves as the 'key'. A substrate binds to the active site of the enzyme to form an enzyme-substrate complex. Enzyme lowers the activation energy of the chemical reaction and thus speeds up the rate of chemical reaction.
Characteristics of enzymes
As enzyme is a protein and the folding of the protein is affected by temperature and pH, the enzyme's activity is affected by temperature and pH.