Q.Which forces are involved in holding the drugs to the active site of enzymes ?

A drug usually binds to an enzyme's active site through weak, non-covalent (reversible) interactions rather than strong covalent bonds, so that the binding is specific but not permanent. The main forces involved are:

• Hydrogen bonds — between polar groups (e.g. $-OH$, $-NH$) on the drug and complementary groups on the enzyme.
• Ionic bonds (electrostatic interactions) — between oppositely charged groups on the drug and the enzyme's active site.
• Dipole–dipole interactions — between polar (but uncharged) parts of the drug and the active site.
• Van der Waals forces — weak attractive forces between non-polar parts of the drug molecule and hydrophobic pockets of the active site. …

Recall that drug–enzyme binding at the active site is non-covalent. List the standard set of weak intermolecular forces: hydrogen bonds, ionic i …

• Saying drugs bind enzymes through covalent bonds (binding is generally non-covalent/reversible). …