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Illustration of a eukaryotic cell membrane Comparison of a eukaryotic vs. a prokaryotic cell membrane. The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of a cell from the outside environment (the extracellular space).
Passive diffusion across a cell membrane.. Passive transport is a type of membrane transport that does not require energy to move substances across cell membranes. [1] [2] Instead of using cellular energy, like active transport, [3] passive transport relies on the second law of thermodynamics to drive the movement of substances across cell membranes.
To enable the membrane as a whole to grow evenly, half of the new phospholipid molecules then have to be transferred to the opposite monolayer. This transfer is catalyzed by enzymes called flippases. In the plasma membrane, flippases transfer specific phospholipids selectively, so that different types become concentrated in each monolayer. [5]
All plasma membranes have an electrical potential across them, with the inside usually negative with respect to the outside. [3] The membrane potential has two basic functions. First, it allows a cell to function as a battery, providing power to operate a variety of "molecular devices" embedded in the membrane. [ 4 ]
In cellular biology, membrane transport refers to the collection of mechanisms that regulate the passage of solutes such as ions and small molecules through biological membranes, which are lipid bilayers that contain proteins embedded in them. The regulation of passage through the membrane is due to selective membrane permeability – a ...
Alpha-helical proteins are present in the inner membranes of bacterial cells or the plasma membrane of eukaryotic cells, and sometimes in the bacterial outer membrane. [5] This is the major category of transmembrane proteins. In humans, 27% of all proteins have been estimated to be alpha-helical membrane proteins. [6]
Protoplasm (/ ˈ p r oʊ t ə ˌ p l æ z əm /; [1] [2] pl. protoplasms) [3] is the part of a cell that is surrounded by a plasma membrane.It is a mixture of small molecules such as ions, monosaccharides, amino acids, and macromolecules such as proteins, polysaccharides, lipids, etc.
The sodium-calcium exchanger (often denoted Na + /Ca 2+ exchanger, exchange protein, or NCX) is an antiporter membrane protein that removes calcium from cells. It uses the energy that is stored in the electrochemical gradient of sodium (Na +) by allowing Na + to flow down its gradient across the plasma membrane in exchange for the countertransport of calcium ions (Ca 2+).