chirality

In chemistry, property of a molecule that indicates that it cannot be superimposed on its mirror image. The mirror image versions of a chiral molecule (called enantiomers) have the same type, number, and ratio of atoms, but differ in the orientation of these atoms within the molecular structure. The term implies ‘handedness’; the relationship of the molecule with its mirror image is that between a right and left hand. The two forms of a chiral compound may have different chemical properties, so it is important to be able to distinguish between them.

Among biomolecules, all standard amino acids except glycine are chiral, as are the building blocks of nucleic acids and carbohydrates such as glucose and fructose. Enzymes catalysing reactions of chiral molecules will usually be specific for one enantiomer only.

Solutions of chiral molecules containing only one enantiomer display optical phenomena known as optical rotation and circular dichroism, which are used in spectroscopy of biomolecules. Mixtures containing both versions in equal amounts will have no such optical properties and are called racemates.