Molecular binding

Molecular binding is an attractive interaction between two molecules which results in a stable association in which the molecules are in close proximity to each other. The result of molecular binding is formation of a molecular complex.

Types
Molecular binding can be classified into the following types:


 * non-covalent – no chemical bonds are formed between the two interacting molecules hence the association is fully reversible
 * reversible covalent – a chemical bond is formed, however the free energy difference separating the non-bonded reactants from bonded product is near equilibrium and the activation barrier is relatively low such that the reverse reaction which cleaves the chemical bond easily occurs
 * irreversible covalent – a chemical bond is formed in which the product is thermodynamically much more stable than the reactants such that the reverse reaction does not take place.

Examples
Molecules that can participate in molecular binding include proteins, nucleic acids, carbohydrates, lipids, and small organic molecules such as drugs. Hence the types of complexes that form as a result of molecular binding include:


 * protein – protein
 * protein – DNA
 * protein – hormone
 * protein – drug

Proteins that form stable complexes with other molecules are often referred to as receptors while their binding partners are called ligands.