Explain the catalytic action of enzymes.

(N/A) For understanding the interaction between a drug and an enzyme,it is important to know how enzymes catalyse the reaction. In their catalytic activity,enzymes perform two major functions:
$(i)$ The first function of an enzyme is to hold the substrate for a chemical reaction. Active sites of enzymes hold the substrate molecule in a suitable position,so that it can be attacked by the reagent effectively. Substrates bind to the active site of the enzyme through a variety of interactions such as ionic bonding,hydrogen bonding,van der Waals interaction,or dipole-dipole interaction.
$(ii)$ The second function of an enzyme is to provide functional groups that will attack the substrate and carry out the chemical reaction.
Macromolecules of biological origin that perform various functions in the body are called enzymes; those which are crucial to the communication system in the body are called receptors.