Drawing of a cell membrane A component of every biological cell, the selectively permeable cell membrane (or plasma membrane or plasmalemma) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. It separates a cell's interior from its surroundings and controls what moves in and out. Cell surface membranes often contain receptor proteins and cell adhesion proteins. There are also other proteins with a variety of functions. These membrane proteins are important for the regulation of cell behavior and the organization of cells in tissues. Schematic three dimensional cross section of a cell membrane. ...
Schematic three dimensional cross section of a cell membrane. ...
Cells in culture, stained for keratin (red) and DNA (green) The cell is the structural and functional unit of all living organisms, sometimes called the building blocks of life. ...
A DPPC bilayer simulation Color scheme: PO4 = green, N(CH3)3 = violet, water = blue, terminal CH3 = yellow, O = red, glycol C = brown, chain C = grey In biology and chemistry, a lipid bilayer is a membrane or zone of membrane composed only of lipid. ...
Two schematic representations of a phospholipid. ...
A representation of the 3D structure of myoglobin, showing coloured alpha helices. ...
In science, a molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. ...
Cells in culture, stained for keratin (red) and DNA (green) The cell is the structural and functional unit of all living organisms, sometimes called the building blocks of life. ...
Transmembrane receptors are integral membrane proteins, which reside and operate typically within a cells plasma membrane, but also in the membranes of some subcellular compartments and organelles. ...
Schematic of cell adhesion The study of cell adhesion is part of cell biology. ...
In animal cells, the cell membrane establishes this separation alone, whereas in yeast, bacteria and plants an additional cell wall forms the outermost boundary, providing primarily mechanical support. The plasma membrane is only about 10 nm thick and may be discerned only faintly with a transmission electron microscope. One of the key roles of the membrane is to maintain the cell potential. Phyla Porifera (sponges) Ctenophora (comb jellies) Cnidaria Placozoa Bilateria Acoelomorpha Orthonectida Rhombozoa Myxozoa Superphylum Deuterostomia Chordata (vertebrates, etc. ...
A cell wall is a more or less solid layer surrounding a cell. ...
A nanometre (American spelling: nanometer, symbol: nm) is 1. ...
Transmission electron microscopy (TEM) is an imaging technique whereby a beam of electrons is focused onto a specimen causing an enlarged version to appear on a fluorescent screen or layer of photographic film (see electron microscope), or can be detected by a CCD camera. ...
In biological cells that are electrically at rest, the cytosol possesses a uniform electric potential or voltage compared to the extracellular solution. ...
A Fluid Mosaic
The basic composition and structure of the plasma membrane is the same as that of the membranes that surround organelles and other subcellular compartments. The foundation is a phospholipid bilayer, and the membrane as a whole is often described as a 'fluid mosaic' - a two-dimensional fluid of freely diffusing lipids, dotted or embedded with proteins which may function as channels or transporters across the membrane, or as receptors. Some of these proteins simply adhere to the membrane (extrinsic or peripheral proteins), while others might be said to reside within it or to span it (intrinsic proteins -- more at integral membrane protein). Glycoproteins have carbohydrates attached to their extracellular domains. Cells may vary the variety and the relative amounts of different lipids to maintain the fluidity of their membranes despite changes in temperature. Cholesterol molecules (in case of eukaryotes) or hopanoids (in case of prokaryotes) in the bilayer assist in regulating fluidity. In cell biology, an organelle is one of several structures with specialized functions, suspended in the cytoplasm of a eukaryotic cell. ...
A DPPC bilayer simulation Color scheme: PO4 = green, N(CH3)3 = violet, water = blue, terminal CH3 = yellow, O = red, glycol C = brown, chain C = grey In biology and chemistry, a lipid bilayer is a membrane or zone of membrane composed only of lipid. ...
Integral membrane protein of the transmembrane type An Integral Membrane Protein (IMP) is a protein molecule (or assembly of proteins) that in most cases spans the biological membrane with which it is associated (especially the plasma membrane) or which, in any case, is sufficiently embedded in the membrane to remain...
Cholesterol is a steroid lipid, found in the cell membranes of all body tissues, and transported in the blood plasma of all animals. ...
Detailed Structure In fact, not all lipid molecules in the cell membrane are "fluid," in the sense of free to diffuse. Lipid rafts and caveolae are examples of more cohesive membrane regions. Across the membrane globally, also many proteins are not entirely free to diffuse. The cytoskeleton undergirds the cell membrane and provides anchoring points for integral membrane proteins. Anchoring restricts them to a particular cell face or surface--for example, the "apical" surface of epithelial cells that line the vertebrate gut--and limits how far they may diffuse within the bilayer. Finally, rather than presenting always a formless and fluid contour, the plasma membrane surface of cells may show structure. Returning to the example of epithelial cells in the gut, the apical surfaces of many such cells are dense with involutions, all similar in size. The finger-like projections, called "microvilli", increase cell surface area and facilitate the absorption of molecules from the outside. Synapses are another example of highly structured membrane. Lipid rafts are cholesterol-rich microdomains in cell membranes. ...
In biology, caveolae (Latin for little caves) are small invaginations of the plasma membrane in many cell types, especially in endothelial cells. ...
The cytoskeleton is a cellular scaffolding or skeleton contained, as all other organelles, within the cytoplasm. ...
In zootomy, epithelium is a tissue composed of a layer of cells. ...
Typical classes Petromyzontidae (lampreys) Placodermi - extinct Chondrichthyes (cartilaginous fish) Acanthodii - extinct Actinopterygii (ray-finned fish) Actinistia (coelacanths) Dipnoi (lungfish) Amphibia (amphibians) Reptilia (reptiles) Aves (birds) Mammalia (mammals) Vertebrata is a subphylum of chordates, specifically, those with backbones or spinal columns. ...
The gastrointestinal or digestive tract, also referred to as the GI tract or the alimentary canal or the gut, is the system of organs within multicellular animals which takes in food, digests it to extract energy and nutrients, and expels the remaining waste. ...
Synapses allow nerve cells to communicate with one another through axons and dendrites, converting electrical signals into chemical ones. ...
Transport across membranes As a lipid bilayer, the cell membrane is selectively permeable. This means that only some molecules can pass unhindered in or out of the cell. These molecules are either small or lipophilic. Other molecules can pass in or out of the cell, if there are specific transport molecules. In chemistry, hydrophobic or lipophilic species, or hydrophobes, tend to be electrically neutral and nonpolar, and thus prefer other neutral and nonpolar solvents or molecular environments. ...
Depending on the molecule, transport occurs by different mechanisms, which can be separated into those that do not consume energy in the form of ATP (passive transport) and those that do (active transport): Adenosine triphosphate (ATP) Adenosine triphosphate (ATP) is the nucleotide known in biochemistry as the molecular currency of intracellular energy transfer; that is, ATP is able to store and transport chemical energy within cells. ...
Passive transport Passive transport is a means of moving different chemical substances across membranes through diffusion of hydrophobic (non polar) and small polar molecules, or facilitated diffusion of polar and ionic molecules, which relies on a transport protein to provide a channel or bind to specific molecules. This spontaneous process decreases free energy, and increases entropy in a system. Unlike active transport, this process does not involve chemical energy (ATP). Passive transport is a means of moving biochemicals, and other atomic or molecular substances, across membranes. ...
Diffusion is the spontaneous spreading of something such as particles, heat, or momentum. ...
In chemistry, hydrophobic or lipophilic species, or hydrophobes, tend to be electrically neutral and nonpolar, and thus prefer other neutral and nonpolar solvents or molecular environments. ...
A transport protein is a protein involved in facilitated diffusion. ...
Adenosine triphosphate (ATP) Adenosine triphosphate (ATP) is the nucleotide known in biochemistry as the molecular currency of intracellular energy transfer; that is, ATP is able to store and transport chemical energy within cells. ...
Active transport Typically moves molecules against their electrochemical gradient, a process that would be entropically unfavorable were it not stoichiometrically coupled with the hydrolysis of ATP. This coupling can be either primary or secondary. In the primary active transport, transporters that move molecules against their electrical/chemical gradient, hydrolyze ATP. In the secondary active transport, transporters use energy derived from transport of another molecule in the direction of their gradient, to move other molecules in the direction against their gradient. This can be either symport (in the same direction) or antiport (in the opposite direction). See also: active transport. The thermodynamic entropy S, often simply called the entropy in the context of thermodynamics, is a measure of the amount of energy in a physical system that cannot be used to do work. ...
In chemistry, stoichiometry is the study of the combination of elements in chemical reactions. ...
A symporter, also known as a coporter, is an integral membrane protein that is involved in facilitated diffusion. ...
An antiporter is an integral membrane protein that is involved in facilitated diffusion. ...
Active transport is the mediated transport of biochemicals, and other atomic/molecular substances, across membranes. ...
Examples include:
- endocytosis
- exocytosis, in which molecules packaged in membrane vesicles are either imported or exported, respectively. Molecular exchangers, transporters and pumps represent other examples.
Endocytosis is a process whereby cells absorb material (molecules or other cells) outside their cell membranes. ...
Exocytosis is the process of a biological cell releasing substances into the extracellular fluid (its environment). ...
In cell biology, a vesicle is a relatively small and enclosed compartment, separated from the cytosol by at least one lipid bilayer. ...
ATPases are a class of enzymes that catalyze the decomposition of adenosine triphosphate (ATP) into adenosine diphosphate (ADP) and a free phosphate ion. ...
References - R.R. Dogonadze, Z.D. Urushadze, "Investigation of the Electrochemical Processes on the Border of Division Electrolite-Biological Membrane", Dep. VINITI (No 3633-71), Moscow, 1971, 20 pp. (In Russian)
- Z.D. Urushadze, "The Charge Transfer Across the Model Biological Membrane".- Proceedings of the Georgian Academy of Sciences, Series of Biology, 12, No 5, 1986, pp. 347-352 (In Russian, English summary)
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