cytoplasmamembranet

The cytoplasmamembranet, often referred to as the cytoplasmic membrane or, in bacteria and archaea, the plasma membrane, is a phospholipid bilayer that encloses the cytoplasm and forms the cell’s boundary. It is composed primarily of amphipathic lipids with embedded proteins, and it may include glycolipids and sterols (such as cholesterol in eukaryotes) that influence fluidity and permeability.

In all domains of life, the membrane is dynamic. The fluid mosaic model describes a bilayer in which lipids diffuse laterally and proteins float within the matrix. In bacteria and archaea the cytoplasmic membrane is the inner boundary; Gram-negative bacteria possess an outer membrane separated by periplasm, whereas in eukaryotes the plasma membrane sits at the cell surface and internal membranes define organelles.

Functions include selective permeability via channels, transporters, and pumps; maintenance of ion gradients and membrane potential; energy transduction (for example, proton motive force driving ATP synthesis in respiration and photosynthesis); signal transduction through membrane receptors; secretion and assembly of cell envelope components; and involvement in cell division and maintenance of cell shape.

Transport and regulation involve diffusion for small uncharged molecules; facilitated diffusion for larger polar molecules; active transport using ATP or proton motive force; and co-transporters for nutrients. Pathogens can exploit or disrupt membranes, and many antibiotics target membrane integrity or the synthesis of cell envelope components. The cytoplasmamembranet thus plays a central role in metabolism, communication, and interaction with the environment.