membraanbound

Membrane-bound, in biology, refers to molecules, organelles, or compartments that are associated with or enclosed by a biological membrane, typically a lipid bilayer. The term contrasts with soluble or cytosolic components that are not enclosed by membranes. Membranes create distinct compartments, regulate transport, and organize biochemical processes within the cell.

Examples include membrane-bound organelles such as the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, and vacuoles in eukaryotic cells, as well as chloroplasts in plants and algae. Membrane-bound vesicles and other compartments enable targeted trafficking and storage of cellular cargo. In prokaryotes, processes often occur at the cytoplasmic membrane or at internal membranes that perform similar roles.

Molecules can be membrane-bound in several ways. Integral membrane proteins span the bilayer; peripheral membrane proteins loosely associate with the membrane surface; and lipid-anchored proteins are covalently linked to membrane lipids. Ribosomes associated with the rough endoplasmic reticulum are membrane-bound, whereas free ribosomes reside in the cytosol. The membrane association can influence protein folding, activity, and interactions, and it helps define the functional specialization of cellular regions.

Studying membrane-bound components often involves separating membrane fractions from soluble cytosol through cell fractionation and differential or density-gradient centrifugation. Solubilization with detergents or other agents is used to extract membrane-associated proteins for analysis.