Noncovalent Interactions

Introduction to Protein Structure

Interactions (bonds) between atoms fall in to two categories: covalent and noncovalent. For small organic molecules it is convienent to think about covalent bonds as intramolecular (i.e as defining the structure of the molecule) and noncovalent interactions as intermolecular. This view is not useful for macromolecules such as proteins; in this case both covalent bonding and intramolecular noncovalent bonding are important in determining the structure of these molecules.

Covalent and noncovalent bonds differ in their strength. Covalent bonds, resulting from the sharing of an electron pair between two atoms are the strongest. Noncovalent interactions are somewhat weaker.

Noncovalent interactions arise via a number of different mechanisms. They include van der Walls interactions, hydrogen bonding, and electrostatic interactions (also called ionic bonding).

van der Walls Interactions

are weak interactions found in all molecules. These interactions are the result of dipole-dipole interactions formed via transient inhomogenieties in the electrons within a molecule.

Hydrogen Bonds

involved the weak sharing of an electron pair between a hydrogen atom and another atom.

Ionic Bonds

are the result of the attraction between groups with opposite electrical charges.