Enzymes are made up of protein. They shows 3/4% structure of protein.
They are globular and found in protoplasm in colloidal form .
Enzymes are biocatalyst. They increase the rate of reactions by lowering the energy of activation and they remain unchanged after reaction and can be used for further reactions. They works as contact catalyst.
They are sensitive to changes in pH and temperature.
There are following theories to explain the mode of action of enzymes-