Cell membrane
Say it: SEL MEM-brayn
The cell membrane is the thin, flexible boundary of lipids and proteins that encloses every cell and controls what enters and leaves it.
Also: plasma membrane, plasmalemma, cytoplasmic membrane, cell membranes
Definition
What is the cell membrane?
The cell membrane, or plasma membrane, is the outer boundary of every cell, separating the cytoplasm from the fluid around it. Its basic structure is a phospholipid bilayer: two sheets of phospholipid molecules with their water-attracting phosphate heads facing outward and their water-repelling fatty acid tails tucked inside. In animal cells, cholesterol sits among the phospholipids and helps keep the membrane fluid over a range of temperatures.
Proteins are embedded in or attached to the bilayer, and many carry sugar chains on the outer surface. The fluid mosaic model, proposed by Singer and Nicolson in 1972, describes this arrangement as a moving patchwork of lipids and proteins rather than a rigid sheet. Because its oily core blocks ions and most polar molecules, the membrane is selectively permeable: small nonpolar molecules cross it directly, while other substances need channels, carriers, pumps or vesicles.
Membrane proteins also serve as receptors for hormones and other signals, and surface sugar-protein complexes let cells recognize one another. Plants, fungi and most bacteria have a tougher cell wall outside the membrane, but the membrane is what controls exchange.
Word parts
Where does the term “cell membrane” come from?
- cell
- small roomLatin cella
- membrane
- thin skin, parchmentLatin membrana
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Related
Terms that go with it
- LipidA lipid is one of a varied group of biological molecules, including fats, oils, phospholipids, waxes and steroids, that do not dissolve in water.
- CholesterolCholesterol is a waxy steroid lipid found in animal cell membranes and used to make steroid hormones, vitamin D and the bile salts that digest fat.
- DiffusionDiffusion is the net movement of molecules from a region of higher concentration to one of lower concentration, driven by their random motion.
- Active transportActive transport is the movement of a substance across a cell membrane against its concentration gradient, powered by energy, usually from ATP.
- ReceptorA receptor is a protein, on a cell's surface or inside it, that binds a specific signaling molecule and triggers a response in the cell.
- OsmosisOsmosis is the diffusion of water across a selectively permeable membrane, from the side with fewer dissolved solutes to the side with more.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- OpenStax Biology 2e, 5.1 Components and Structure
- NHGRI Talking Glossary: Cell Membrane
- MeSH (NLM): Cell Membrane
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