A knowledge of the physiological function
Drugs interact with macromolecules like proteins, carbohydrates, lipids and nucleic acids and hence, these are called target molecules.
Proteins perform several roles in the body. Proteins which act as biological catalysts are called enzymes, those which are involved in communication system are called receptors.
Carrier proteins carry polar molecules across the cell membrane.
Nucleic acids have coded genetic information in the cell, while lipids and carbohydrates form structural part of cell ' membranes.