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Encyclopedia > Cell membrane

The cell membrane (also called the plasma membrane, plasmalemma or "phospholipid bilayer") is a selectively permeable lipid bilayer found in all cells.[1] It contains a wide variety of biological molecules, primarily proteins and lipids, which are involved in a vast array of cellular processes such as cell adhesion, ion channel conductance and cell signaling. The plasma membrane also serves as the attachment point for both the intracellular cytoskeleton and, if present, the cell wall. Partially permeable is a biological term which describes the characteristic of a barrier to selectively allow substances to pass through. ... This fluid lipid bilayer cross section is made up entirely of phosphatidylcholine. ... Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell being used to describe the smallest unit of a living organism Cells in culture, stained for keratin (red) and DNA (green) The cell is the... 3D (left and center) and 2D (right) representations of the terpenoid molecule atisane. ... A representation of the 3D structure of myoglobin showing coloured alpha helices. ... Figure 1: Basic lipid structure. ... The eukaryotic cytoskeleton. ... Plant cells separated by transparent cell walls. ...

Illustration of a cell membrane

Contents

Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ...

Function

The cell membrane surrounds the cytoplasm of a cell and, in animal cells, physically separates the intracellular components from the extracellular environment, thereby serving a function similar to that of skin. In fungi, some bacteria, and plants, an additional cell wall forms the outermost boundary; however, the cell wall plays mostly a mechanical support role rather than a role as a selective boundary. The cell membrane also plays a role in anchoring the cytoskeleton to provide shape to the cell, and in attaching to the extracellular matrix to help group cells together in the formation of tissues. Schematic showing the cytoplasm, with major components of a typical animal cell. ... This article is about the organ. ... Divisions Chytridiomycota Zygomycota Ascomycota Basidiomycota The Fungi (singular: fungus) are a large group of organisms ranked as a kingdom within the Domain Eukaryota. ... Phyla Actinobacteria Aquificae Chlamydiae Bacteroidetes/Chlorobi Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Lentisphaerae Nitrospirae Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Verrucomicrobia Bacteria (singular: bacterium) are unicellular microorganisms. ... u fuck in ua ... The eukaryotic cytoskeleton. ... Illustration depicting extracellular matrix (basement membrane and interstitial matrix) in relation to epithelium, endothelium and connective tissue In biology, the extracellular matrix (ECM) is the extracellular part of animal tissue that usually provides structural support to the cells in addition to performing various other important functions. ... Biological tissue is a group of cells that perform a similar function. ...


The barrier is selectively permeable and able to regulate what enters and exits the cell, thus facilitating the transport of materials needed for survival. The movement of substances across the membrane can be either passive, occurring without the input of cellular energy, or active, requiring the cell to expend energy in moving it. The membrane also maintains the cell potential. Scheme of semipermeable membrane during hemodialysis, where red is blood, blue is the dialysing fluid, and yellow is the membrane. ... In biological cells that are electrically at rest, the cytosol possesses a uniform electric potential or voltage compared to the extracellular solution. ...


Specific proteins embedded in the cell membrane can act as molecular signals that allow cells to communicate with each other. Protein receptors are found ubiquitously and function to receive signals from both the environment and other cells. These signals are transduced into a form that the cell can use to directly effect a response. Other proteins on the surface of the cell membrane serve as "markers" that identify a cell to other cells. The interaction of these markers with their respective receptors forms the basis of cell-cell interaction in the immune system. In biochemistry, a receptor is a protein on the cell membrane or within the cytoplasm or cell nucleus that binds to a specific molecule (a ligand), such as a neurotransmitter, hormone, or other substance, and initiates the cellular response to the ligand. ... In biology, signal transduction refers to any process by which a cell converts one kind of signal or stimulus into another, most often involving ordered sequences of biochemical reactions inside the cell, that are carried out by enzymes and linked through second messengers resulting in what is thought of as... A scanning electron microscope image of a single neutrophil (yellow), engulfing anthrax bacteria (orange). ...


Structure

Lipid bilayer

Diagram of the arrangement of amphipathic lipid molecules to form a lipid bilayer. The yellow polar head groups separate the grey hydrophobic tails from the aqueous cytosolic and extracellular environments.
Diagram of the arrangement of amphipathic lipid molecules to form a lipid bilayer. The yellow polar head groups separate the grey hydrophobic tails from the aqueous cytosolic and extracellular environments.

The cell membrane consists primarily of a thin layer of amphipathic phospholipids which spontaneously arrange so that the hydrophobic "tail" regions are shielded from the surrounding polar fluid, causing the more hydrophilic "head" regions to associate with the cytosolic and extracellular faces of the resulting bilayer. This forms a continuous, spherical lipid bilayer approximately 7 nm thick, barely discernible with a transmission electron microscope.[1] Image File history File links Fluid_Mosaic. ... Image File history File links Fluid_Mosaic. ... This fluid lipid bilayer cross section is made up entirely of phosphatidylcholine. ... A commonly-used example of a polar compound is water (H2O). ... It has been suggested that this article or section be merged with Amphiphiles. ... Two schematic representations of a phospholipid. ... This fluid lipid bilayer cross section is made up entirely of phosphatidylcholine. ... A nanometre (American spelling: nanometer, symbol nm) (Greek: νάνος, nanos, dwarf; μετρώ, metrό, count) is a unit of length in the metric system, equal to one billionth of a metre (or one millionth of a millimetre), which is the current SI base unit of length. ... 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. ...


The arrangement of hydrophilic and hydrophobic heads of the lipid bilayer prevent polar solutes (e.g. amino acids, nucleic acids, carbohydrates, proteins, and ions) from diffusing across the membrane, but generally allows for the passive diffusion of hydrophobic molecules. This affords the cell the ability to control the movement of these substances via transmembrane protein complexes such as pores and gates. A transmembrane protein is a protein that spans the entire biological membrane. ...


Flippases and Scramblases concentrate phosphatidyl serine, which carries a negative charge, on the inner membrane. Along with NANA, this creates an extra barrier to charged moities moving through the membrane. Flippases (rarely, flipases) are enzymes located in the membrane responsible for aiding the movement of phospholipid molecules between the two leaflets that compose a cells membrane (transverse diffusion). ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Phosphatidylserine is a phospholipid nutrient found in fish, green leafy vegetables, soybeans and rice, and is essential for the normal functioning of neuronal cell membranes. ... Sialic acid is a generic term for the N- or O-substituted derivatives of neuraminic acid, a nine-carbon monosaccharide. ... Look up moiety in Wiktionary, the free dictionary. ...


Membranes serve diverse functions in eukaryotic and prokaryotic cells. One important role is to regulate the movement of materials into and out of cells. The phospholipid bilayer structure (fluid mosaic model) with specific membrane proteins accounts for the selective permeability of the membrane and passive and active transport mechanisms. In addition, membranes in prokaryotes and in the mitochondria and chloroplasts of eukaryotes facilitate the synthesis of ATP through chemiosmosis.


Integral membrane proteins

The cell membrane contains many integral membrane proteins, which pepper the entire surface. These structures, which can be visualized by electron microscopy or fluorescence microscopy, can be found on the inside of the membrane, the outside, or membrane spanning. These may include integrins, cadherins, desmosomes, clathrin-coated pits, caveolaes, and different structures involved in cell adhesion. An Integral Membrane Protein (IMP) is a protein molecule (or assembly of proteins) that is permanently attached to the biological membrane. ... The electron microscope is a microscope that can magnify very small details with high resolving power due to the use of electrons rather than light to scatter off material, magnifying at levels up to 500,000 times. ... Microscopy is any technique for producing visible images of structures or details too small to otherwise be seen by the human eye. ... A transmembrane protein is a protein that spans the entire biological membrane. ... An integrin, or integrin receptor, is an integral membrane protein in the plasma membrane of cells. ... Cadherins are a class of proteins which are expressed on the surface of cells. ... Cell adhesion in desmosomes A desmosome (also known as macula adherens (Latin for adhering spot ) is a cell structure specialized for cell-to-cell adhesion. ... Clathrin is a protein that is the major constituent of the coat of the coated pits and coated vesicles formed during endocytosis of materials at the surface of cells. ... In biology, caveolae (Latin for little caves) are small invaginations of the plasma membrane in many cell types, especially in endothelial cells. ... Schematic of cell adhesion The study of cell adhesion is part of cell biology. ...


Membrane skeleton

The cytoskeleton is found underlying the cell membrane in the cytoplasm and provides a scaffolding for membrane proteins to anchor to, as well as forming organelles that extend from the cell. Anchoring proteins restricts them to a particular cell surface — for example, the apical surface of epithelial cells that line the vertebrate gut — and limits how far they may diffuse within the bilayer. The cytoskeleton is able to form appendage-like organelles, such as cilia, which are covered by the cell membrane and project from the surface of the cell. The apical surfaces of the aforementioned epithelial cells are dense with finger-like projections, called microvilli, which increase cell surface area and thereby increase the absorption rate of nutrients. The cell membrane acts as a protecting body. The eukaryotic cytoskeleton. ... In zootomy, epithelium is a tissue composed of a layer of cells. ... This article does not cite any references or sources. ... Gut redirects here. ... cross-section of two cilia, showing 9+2 structure A cilium (plural cilia) is a fine projection from a eukaryotic cell that constantly beats in one direction. ... Categories: Stub ...


Structure and the Fluid mosaic model

According to the fluid mosaic model of S. J. Singer and Garth Nicolson, the biological membranes can be considered as a two-dimensional liquid where all lipid and protein molecules diffuse more or less freely[2]. This picture may be valid in the space scale of 10 nm. However, the plasma membranes contain different structures or domains that can be classified as (a) protein-protein complexes; (b) lipid rafts, (c) pickets and fences formed by the actin-based cytoskeleton; and (d) large stable structures, such as synapses or desmosomes. A lipid raft is a cholesterol-enriched microdomain in cell membranes. ... The eukaryotic cytoskeleton. ...


The fluid mosaic model can be seen when the membrane proteins of two cells (e.g., a human cell and a mouse cell) are tagged with different-coloured fluorescent labels. When the two cells are fused, the two colours intermix, indicating that the proteins are free to move in the 2D plane.


Composition

Cell membranes contain a variety of biological molecules, notable lipids and proteins. Material is incorporated into the membrane, or deleted from it, by a variety of mechanisms:

  • Fusion of intracellular vesicles with the membrane (exocytosis) not only excretes the contents of the vesicle but also incorporates the vesicle membrane's components into the cell membrane. The membrane may form blebs around extracellular material that pinch off to become vesicles (endocytosis).
  • If a membrane is continuous with a tubular structure made of membrane material, then material from the tube can be drawn into the membrane continuously.
  • Although the concentration of membrane components in the aqueous phase is low (stable membrane components have low solubility in water), exchange of molecules with this small reservoir is possible.

In all cases, the mechanical tension in the membrane has an effect on the rate of exchange. In some cells, usually having a smooth shape, the membrane tension and area are interrelated by elastic and dynamical mechanical properties, and the time-dependent interrelation is sometimes called homeostasis, area regulation or tension regulation. In cell biology, a vesicle is a relatively small and enclosed compartment, separated from the cytosol by at least one lipid bilayer. ... Neuron A (transmitting) to neuron B (receiving) 1. ... Endocytosis (IPA: ) is a process whereby cells absorb material (molecules such as proteins) from the outside by engulfing it with their cell membrane. ... Homeostasis (from Greek: ὅμος, homos, equal; and ιστημι, histemi, to stand lit. ...


Lipids

Examples of the major membrane phospholipids and glycolipids: phosphatidylcholine (PtdCho), phosphatidylethanolamine (PtdEtn), phosphatidylinositol (PtdIns), phosphatidylserine (PtdSer).
Examples of the major membrane phospholipids and glycolipids: phosphatidylcholine (PtdCho), phosphatidylethanolamine (PtdEtn), phosphatidylinositol (PtdIns), phosphatidylserine (PtdSer).

The cell membrane consists of three classes of amphipathic lipids: phospholipids, glycolipids, and steroids. The amount of each depends upon the type of cell, but in the majority of cases phospholipids are the most abundant.[3] In RBC studies, 30% of the plasma membrane is lipid. Image File history File links Download high-resolution version (579x607, 10 KB) I, the creator of this work, hereby release it into the public domain. ... Image File history File links Download high-resolution version (579x607, 10 KB) I, the creator of this work, hereby release it into the public domain. ... Lecithin, also known as Phosphatidylcholine Lecithin is usually used as synonym for phosphatidylcholine, a phospholipid which is the major component of a phosphatide fraction which may be isolated from either egg yolk (in Greek lekithos - λεκιθος), or soy beans. ... Phosphatidylethanolamine is a lipid found in biological membranes. ... Chemical structure of sn-1-stearoyl-2-arachidonoyl phosphatidylinositol Phosphatidylinositol (abbreviated PtdIns, or PI) is a minor phospholipid component of eukaryotic cell membranes. ... Phosphatidylserine is a phospholipid nutrient found in fish, green leafy vegetables, soybeans and rice, and is essential for the normal functioning of neuronal cell membranes. ... It has been suggested that this article or section be merged with Amphiphiles. ... Phospholipid Two schematic representations of a phospholipid. ... Glycolipids are carbohydrate-attached lipids. ... This article is about the chemical family of steroids. ... “Red cell” redirects here. ...


The fatty chains in phospholipids and glycolipids usually contain an even number of carbon atoms, typically between 14 and 24. The 16- and 18-carbon fatty acids are the most common. Fatty acids may be saturated or unsaturated, with the configuration of the double bonds nearly always cis. The length and the degree of unsaturation of fatty acids chains have a profound effect on membranes fluidity[4] as unsaturated lipids create a kink, preventing the fatty acids from packing together as tightly, thus decreasing the melting point (increasing the fluidity) of the membrane. The ability of some organisms to regulate the fluidity of their cell membranes by altering lipid composition is called homeoviscous adaptation.


The entire membrane is held together via non-covalent interaction of hydrophobic tails, however the structure is quite fluid and not fixed rigidly in place. Phospholipid molecules in the cell membrane are "fluid" in the sense that they are free to diffuse and exhibit rapid lateral diffusion along the layer in which they are present. However, movement of phospholipid molecules between layers is not energetically favourable and does not occur to an appreciable extent. Lipid rafts and caveolae are examples of cholesterol-enriched microdomains in the cell membrane. Noncovalent bonding refers to a variety of interactions, that are not covalent in nature, between molecules or parts of molecules that provide force to hold the molecules or parts of molecules together usually in a specific orientation or conformation. ... 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. ... Cholesterol is a sterol (a combination steroid and alcohol). ...


In animal cells cholesterol is normally found dispersed in varying degrees throughout cell membranes, in the irregular spaces between the hydrophobic tails of the membrane lipids, where it confers a stiffening and strengthening effect on the membrane.[1]


Carbohydrates

About 5% of the plasma membrane weight is carbohydrate, predominantly glycoprotein, but with some lipoprotein (cerebrosides and gangliosides). For the most part, no glycosylation occurs on other unit membranes, and only ever occurs on the extracellular surface of cell membranes. Lactose is a disaccharide found in milk. ... N-linked protein glycosylation (N-glycosylation of N-glycans) at Asn residues (Asn-x-Ser/Thr motifs) in glycoproteins[1]. Glycoproteins are proteins that contain oligosaccharide chains (glycans) covalently attached to their polypeptide backbones. ... A lipoprotein is a biochemical assembly that contains both proteins and lipids. ... Cerebrosides are glycosphingolipids which are important components in animal muscle and nerve cell membranes. ... Ganglioside is a compound composed of a glycosphingolipid (ceramide and oligosaccharide) with one or more sialic acids (AKA n-acetylneuraminic acid) linked on the sugar chain. ... Glycosylation is the process or result of addition of saccharides to proteins and lipids. ...


The glycocalyx is an important feature in all cells, especially epithelia with microvilli. Recent data suggest the glycocalyx participates in cell adhesion, lymphocyte homing, and many others. It has been suggested that this article or section be merged with Glycocalix. ... This article is about the epithelium as it relates to animal anatomy. ...


The penultimate sugar is galactose and the terminal sugar is sialic acid, as the sugar backbone is modified in the golgi apparatus. Sialic acid carries a negative charge, providing an external barrier to charged particles. Penultimate can mean next to last in a general context, but is used most often in linguistics as an adjective or noun to denote or refer to the penult of a word/ penultimate stress. ... Galactose (also called brain sugar) is a type of sugar found in dairy products, in sugar beets and other gums and mucilages. ... Sialic acid is a generic term for the N- or O-substituted derivatives of neuraminic acid, a nine-carbon monosaccharide. ... Micrograph of Golgi apparatus, visible as a stack of semicircular black rings near the bottom. ...


Proteins

Type Description Examples
Integral proteins
or transmembrane proteins
Span the membrane and have a hydrophilic cytosolic domain, which interacts with internal molecules, a hydrophobic membrane-spanning domain that anchors it within the cell membrane, and a hydrophilic extracellular domain that interacts with external molecules. The hydrophobic domain consists of one, multiple, or a combination of α-helices and β sheet protein motifs. Ion channels, proton pumps, G protein-coupled receptor
Lipid anchored proteins Covalently-bound to single or multiple lipid molecules; hydrophobically insert into the cell membrane and anchor the protein. The protein itself is not in contact with the membrane. G proteins
Peripheral proteins Attached to integral membrane proteins, or associated with peripheral regions of the lipid bilayer. These proteins tend to have only temporary interactions with biological membranes, and, once reacted the molecule, dissociates to carry on its work in the cytoplasm. Some enzymes, some hormones

The cell membrane plays host to a large amount of protein that is responsible for its various activities. The amount of protein differs between species and according to function, however the typical amount in a cell membrane is 50%.[4] These proteins are undoubtedly important to a cell: Approximately a third of the genes in yeast code specifically for them, and this number is even higher in multicellular organisms.[3] 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... The cytosol (cf. ... It has been suggested that Structural domain be merged into this article or section. ... Side view of an α-helix of alanine residues in atomic detail. ... Diagram of β-pleated sheet with H-bonding between protein strands The β sheet (also β-pleated sheet) is the second form of regular secondary structure in proteins — the first is the alpha helix — consisting of beta strands connected laterally by three or more hydrogen bonds, forming a generally twisted, pleated sheet. ... In an unbranched, chain-like biological molecule, such as a protein or a strand of RNA, a structural motif is a three-dimensional structural element or fold within the chain, which appears also in a variety of other molecules. ... Ion channels are pore-forming proteins that help to establish and control the small voltage gradient that exists across the plasma membrane of all living cells (see cell potential) by allowing the flow of ions down their electrochemical gradient. ... proton gradient: Pink represents the matrix while the red dots represent protons. ... A Mu-opioid G protein-coupled receptor with its agonist Figure 1. ... In lipid anchored proteins, a covalently attached fatty acid such as palmitate or myristate serves to anchor them to the cytoplasmic face of the cell membrane. ... G-proteins, short for guanine nucleotide binding proteins, are a family of proteins involved in second messenger cascades. ... Perhipheral and Integral Membrane Proteins Peripheral membrane proteins are proteins that adhere only loosely to the biological membrane with which they are associated. ... This fluid lipid bilayer cross section is made up entirely of phosphatidylcholine. ... Perhipheral and Integral Membrane Proteins Peripheral membrane proteins are proteins that adhere only loosely to the biological membrane with which they are associated. ... Perhipheral and Integral Membrane Proteins Peripheral membrane proteins are proteins that adhere only loosely to the biological membrane with which they are associated. ... For other uses, see Gene (disambiguation). ... Typical divisions Ascomycota (sac fungi) Saccharomycotina (true yeasts) Taphrinomycotina Schizosaccharomycetes (fission yeasts) Basidiomycota (club fungi) Urediniomycetes Sporidiales Yeasts are a growth form of eukaryotic micro organisms classified in the kingdom Fungi, with about 1,500 species described;[1] they dominate fungal diversity in the oceans. ...


The cell membrane, being exposed to the outside environment, is an important site of cell-cell communication. As such, a large variety of protein receptors and identification proteins, such as antigens, are present on the surface of the membrane. Functions of membrane proteins can also include cell-cell contact, surface recognition, cytoskeleton contact, signalling, enzymic activity, or transporting substances across the membrane. In biochemistry, a receptor is a protein on the cell membrane or within the cytoplasm or cell nucleus that binds to a specific molecule (a ligand), such as a neurotransmitter, hormone, or other substance, and initiates the cellular response to the ligand. ... An antigen or immunogen is a molecule that stimulates an immune response. ...


Most membrane proteins must be inserted in some way into the membrane. For this to occur, an N-terminus "signal sequence" of amino acids directs proteins to the endoplasmic reticulum, which inserts the proteins into a lipid bilayer. Once inserted, the proteins is then transported to its final destination in vesicles, where the vesicle fuses with the target membrane/ The endoplasmic reticulum or ER is an organelle found in all eukaryotic cells that is an interconnected network of tubules, vesicles and cisternae that is responsible for several specialized functions: Protein translation, folding, and transport of proteins to be used in the cell membrane (e. ... In cell biology, a vesicle is a relatively small and enclosed compartment, separated from the cytosol by at least one lipid bilayer. ...




Variation

The cell membrane has slightly different composition in different cell types and has therefore different denominations in different cell types:

Muscle system The sarcolemma is the cell membrane of a muscle cell. ... Myocyte is the technical term for a muscle cell. ... An oocyte or ovocyte is a female gametocyte that divides twice by mitosis and meiosis into two other oocytes or into two ootids. ...

Permeability

The permeability of membranes is the ease of molecules to pass it. This depends mainly on electric charge and, to a slightly lesser extent, on the molar mass of the molecule. Electrically-neutral and small molecules pass the membrane easier than charged, large ones. This box:      Electric charge is a fundamental conserved property of some subatomic particles, which determines their electromagnetic interaction. ... Molar mass is the mass of one mole of a chemical element or chemical compound. ...


The electric charge phenomenon results in pH parturition of substances throughout the fluid compartments of the body.


See also

There are very few or no other articles that link to this one. ... Bacteria, despite their apparent simplicity contain a well developed cell structure which is responsible for many of their unique biological properties. ... Schematic of cell adhesion The study of cell adhesion is part of cell biology. ... Active efflux is a mechanism responsible for extrusion of toxic substances and antibiotics outside the cell. ... A cell membrane defines a boundary between the living cell and its environment. ... Bacteria that are Gram-negative are not stained dark blue or violet by Gram staining, in contrast to Gram-positive bacteria. ... Gram-positive bacteria are those that are stained dark blue or violet by gram staining, in contrast to Gram-negative bacteria, which are not affected by the stain. ...

References

  1. ^ a b c Alberts B, Johnson A, Lewis J, et al. Molecular Biology of the Cell, 4th ed.. ISBN 0-8153-3218-1. 
  2. ^ The fluid mosaic model of the structure of cell membranes by S. J. Singer and G. L. Nicolson in Science (1972) Volume 175, pages 720-731.
  3. ^ a b Lodish H, Berk A, Zipursky LS, et al (2004). Molecular Cell Biology, 4th ed.. ISBN 0-7167-3136-31986. 
  4. ^ a b Jesse Gray, Shana Groeschler, Tony Le, Zara Gonzalez (2002). Membrane Structure (SWF). Davidson College. Retrieved on 2007-01-11.

Science is the academic journal of the American Association for the Advancement of Science and is considered one of the worlds most prestigious scientific journals. ... Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 11th day of the year in the Gregorian calendar. ...

External links

Wikimedia Commons has media related to:
Cell membrane
In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is separately enclosed within its own lipid membrane. ... Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell being used to describe the smallest unit of a living organism Cells in culture, stained for keratin (red) and DNA (green) The cell is the... In spermatozoa of many animals, the acrosome is an organelle that develops over the anterior half of the spermatozoons head. ... Plant cells separated by transparent cell walls. ... A centriole showing the nine triplets of microtubules. ... Chloroplasts are organelles found in plant cells and eukaryotic algae that conduct photosynthesis. ... Not to be confused with Psyllium. ... For the insect anatomical structure, see Antenna (biology). ... In cell biology, the centrosome is the main microtubule organizing center (MTOC) of the animal cell as well as a regulator of cell-cycle progression. ... Schematic showing the cytoplasm, with major components of a typical animal cell. ... The endoplasmic reticulum or ER is an organelle found in all eukaryotic cells that is an interconnected network of tubules, vesicles and cisternae that is responsible for several specialized functions: Protein translation, folding, and transport of proteins to be used in the cell membrane (e. ... In biology an endosome is a membrane-bound compartment inside cells. ... Micrograph of Golgi apparatus, visible as a stack of semicircular black rings near the bottom. ... Various organelles labeled. ... In a biological cell, a melanosome is an organelle containing melanin, the most common light-absorbing pigment found in the animal kingdom. ... Electron micrograph of a mitochondrion showing its mitochondrial matrix and membranes In cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed organelle that is found in most eukaryotic cells. ... A diagram of the structure of a Myofybril Myofibrils (obsolete term: sarcostyles) are cylindrical organelles, found within muscle cells. ... HeLa cells stained for DNA with the Blue Hoechst dye. ... The nucleolus is contained within the cell nucleus. ... Parenthesomes are found in basidiomycete fungus. ... Basic structure of a peroxisome Peroxisomes are ubiquitous organelles in eukaryotes that participate in the metabolism of fatty acids and other metabolites. ... Plant cells with visible chloroplasts. ... Figure 1: Ribosome structure indicating small subunit (A) and large subunit (B). ... Schematic of typical animal cell, showing subcellular components: (1) nucleolus (2) nucleus (3) ribosome (4) vesicle (5) rough endoplasmic reticulum (ER) (6) Golgi apparatus (7) Cytoskeleton (8) smooth ER (9) mitochondria (10) vacuole (11) cytoplasm (12) lysosome (13) centrioles Vacuoles are found in the cytoplasm of most plant cells and... In cell biology, a vesicle is a relatively small and enclosed compartment, separated from the cytosol by at least one lipid bilayer. ... In biology, caveolae (Latin for little caves) are small invaginations of the plasma membrane in many cell types, especially in endothelial cells. ... A cell junction is a structure within a tissue of a multicellular organism. ... It has been suggested that this article or section be merged with Glycocalix. ... A lipid raft is a cholesterol-enriched microdomain in cell membranes. ... Myelin is an electrically insulating phospholipid layer that surrounds the axons of many neurons. ... This article is about anatomy; for the musical group see Nodes of Ranvier (band) Nodes of Ranvier are regularly spaced gaps in the myelin sheath around an axon or nerve fiber. ... The nuclear envelope (also known as the perinuclear envelope, nuclear membrane, nucleolemma or karyotheca) is the double membrane of the nucleus that encloses genetic material in eukaryotic cells. ... A computer generated 3D view of a phycobilisome showing Phycoerythrin subunits in red, Phycocyanin subunits in dark blue and Allophycocyanin subunits in light blue. ...

  Results from FactBites:
 
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Cellular membrane fusion is well known to scientists, and is one of the most common ways for molecules to enter or exit cells, in processes such as fertilization and viral infection, for example.
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Cells in marine environments are surrounded by a hypertonic solution, and must actively pump ions into their cells to reduce their water potential and so reduce water loss by osmosis.
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