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Subject - Biochemistry, Cell Biology

The plasma or cell membrane is a 6-9 nm thick lipid bilayer made primarily of phospho- and glycolipids. It forms the outer boundary of the cell plasma (cytoplasm) of all cells and is selectively permeable. Transmembrane proteins like channel-forming proteins or carrier proteins control the exchange of materials between the cell and its surroundings, while glycoproteins lodged in or on the cell determine its antigenic properties. The cell membrane is a dynamic structure in that all of its components can shift around relative to each other (according to the fluid mosaic model of Singer and Nicholson, 1972), which allows processes like endocytosis and exocytosis to occur.

For a cell, the membrane has the following primary functions:

  • Regulation of the intracellular environment (pH value, ionic composition) as a necessary condition for all enzymatic processes that occur in the cell
  • Selective exchange of material with the environment: active absorption of nutrients, disposal of toxic substances
  • Formation of ion gradients, for example in excitatory nerve or muscle cells
  • Support for antigenic features relevant for cell-cell recognition

In addition to the cell membrane, also known as the plasmalemma, plant cells also have a cell wall that protects the cells from mechanical effects. This cell wall is made of peptidoglycan (bacteria), chitin (fungi), or cellulose (plants).

See also: eukaryotes , organelles