Cleaving

Cleaving (or cleavage) is the act of splitting or severing along a plane, bond, or interface. The term is used across sciences to describe a break in a structure, often reflecting an underlying plane of weakness or a specific chemical or biochemical site.

In chemistry and biochemistry, cleavage denotes the breaking of chemical bonds within a molecule. It can be homolytic, producing radicals, or heterolytic, yielding ions. Examples include photochemical cleavage of weak bonds to generate reactive radicals, and hydrolytic or oxidative cleavages that split larger molecules into smaller fragments. In biology, cleavage also encompasses proteolytic and nucleolytic processes that activate or mature molecules by cutting peptide or nucleotide sequences.

In geology and mineralogy, cleavage describes a mineral’s tendency to break along flat, parallel surfaces aligned with crystallographic planes. Cleavage is graded as perfect, good, fair, or indistinct, and varies with crystal structure. Minerals such as mica show perfect cleavage along one plane, while quartz has no cleavage and tends to fracture conchoidally.

In biology and medicine, cleavage has several meanings. Embryology uses cleavage to describe rapid mitotic divisions that partition the zygote into progressively smaller cells, producing a multicellular embryo without growth. In molecular biology, cleavage refers to the cutting of nucleic acids by nucleases (or restriction enzymes) and to proteolytic cleavage that activates or matures proteins by removing peptide segments.

In materials science, cleavage fracture is a brittle mode of failure in which a crystal splits along a crystallographic plane under stress, as opposed to ductile fracture that involves plastic deformation.