Capping

Capping is the act of placing a cap or lid on something, or more broadly, setting an upper limit or maximum value for something. The term is used across many fields, often to describe both physical coverings and regulatory or quantitative limits. In many contexts, capping implies finishing or sealing an object, protecting it from exposure or misuse.

In molecular biology, capping refers to the addition of a protective cap to the 5' end of eukaryotic mRNA. This cap is usually a 7-methylguanosine (m7G) connected to the mRNA 5' end by a 5'-5' triphosphate bridge, followed by additional methylations. The cap protects the transcript from exonucleases and promotes initiation of translation and RNA processing.

In immunology, capping describes the redistribution of cell-surface antigens or receptors into a cap at one region of the membrane after cross-linking by antibodies or ligands. This dynamic reorganization is used to study endocytosis and receptor signaling.

In geology and mining, capping can refer to the natural or engineered top layer that seals an underlying formation. Cap rock forms a barrier that limits fluid flow; engineers also cap abandoned wells or landfills by placing sealing layers to prevent leakage.

A capstone is the finishing block on a wall or tower; capping a structure refers to placing such a cap to protect and complete the construction.

In economics and public policy, capping means setting an upper bound, such as spending caps, price caps, or emission caps. Caps are used to control costs, limit price volatility, or reduce environmental impact, often implemented through regulations or market-based instruments.

In manufacturing and packaging, capping is the process of placing a cap on a container, such as a bottle. Capping machines automate this step to seal contents and preserve quality.