Cell membrane

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Illustration of a eukaryotic cell membrane Cell membrane detailed diagram 4.svg
Illustration of a eukaryotic cell membrane
Comparison of a eukaryotic vs. a prokaryotic cell membrane Celltypes.svg
Comparison of a eukaryotic vs. a prokaryotic cell membrane

The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment (the extracellular space). [1] [2] The cell membrane consists of a lipid bilayer, made up of two layers of phospholipids with cholesterols (a lipid component) interspersed between them, maintaining appropriate membrane fluidity at various temperatures. The membrane also contains membrane proteins, including integral proteins that span the membrane and serve as membrane transporters, and peripheral proteins that loosely attach to the outer (peripheral) side of the cell membrane, acting as enzymes to facilitate interaction with the cell's environment. [3] Glycolipids embedded in the outer lipid layer serve a similar purpose. The cell membrane controls the movement of substances in and out of cells and organelles, being selectively permeable to ions and organic molecules. [4] In addition, cell membranes are involved in a variety of cellular processes such as cell adhesion, ion conductivity, and cell signalling and serve as the attachment surface for several extracellular structures, including the cell wall and the carbohydrate layer called the glycocalyx, as well as the intracellular network of protein fibers called the cytoskeleton. In the field of synthetic biology, cell membranes can be artificially reassembled. [5] [6] [7] [8]



While Robert Hooke's discovery of cells in 1665 led to the proposal of the Cell Theory, Hooke misled the cell membrane theory that all cells contained a hard cell wall since only plant cells could be observed at the time. [9] Microscopists focused on the cell wall for well over 150 years until advances in microscopy were made. In the early 19th century, cells were recognized as being separate entities, unconnected, and bound by individual cell walls after it was found that plant cells could be separated. This theory extended to include animal cells to suggest a universal mechanism for cell protection and development. By the second half of the 19th century, microscopy was still not advanced enough to make a distinction between cell membranes and cell walls. However, some microscopists correctly identified at this time that while invisible, it could be inferred that cell membranes existed in animal cells due to intracellular movement of components internally but not externally and that membranes were not the equivalent of a cell wall to a plant cell. It was also inferred that cell membranes were not vital components to all cells. Many refuted the existence of a cell membrane still towards the end of the 19th century. In 1890, an update to the Cell Theory stated that cell membranes existed, but were merely secondary structures. It was not until later studies with osmosis and permeability that cell membranes gained more recognition. [9] In 1895, Ernest Overton proposed that cell membranes were made of lipids. [10]

The lipid bilayer hypothesis, proposed in 1925 by Gorter and Grendel, [11] created speculation in the description of the cell membrane bilayer structure based on crystallographic studies and soap bubble observations. In an attempt to accept or reject the hypothesis, researchers measured membrane thickness. These researchers extracted the lipid from human red blood cells and measured the amount of surface area the lipid would cover when spread over the surface of the water. Since mature mammalian red blood cells lack both nuclei and cytoplasmic organelles, the plasma membrane is the only lipid-containing structure in the cell. Consequently, all of the lipids extracted from the cells can be assumed to have resided in the cells' plasma membranes. The ratio of the surface area of water covered by the extracted lipid to the surface area calculated for the red blood cells from which the lipid was 2:1(approx) and they concluded that the plasma membrane contains a lipid bilayer. [9] [12]

In 1925 it was determined by Fricke that the thickness of erythrocyte and yeast cell membranes ranged between 3.3 and 4 nm, a thickness compatible with a lipid monolayer. The choice of the dielectric constant used in these studies was called into question but future tests could not disprove the results of the initial experiment. Independently, the leptoscope was invented in order to measure very thin membranes by comparing the intensity of light reflected from a sample to the intensity of a membrane standard of known thickness. The instrument could resolve thicknesses that depended on pH measurements and the presence of membrane proteins that ranged from 8.6 to 23.2 nm, with the lower measurements supporting the lipid bilayer hypothesis. Later in the 1930s, the membrane structure model developed in general agreement to be the paucimolecular model of Davson and Danielli (1935). This model was based on studies of surface tension between oils and echinoderm eggs. Since the surface tension values appeared to be much lower than would be expected for an oil–water interface, it was assumed that some substance was responsible for lowering the interfacial tensions in the surface of cells. It was suggested that a lipid bilayer was in between two thin protein layers. The paucimolecular model immediately became popular and it dominated cell membrane studies for the following 30 years, until it became rivaled by the fluid mosaic model of Singer and Nicolson (1972). [13] [9]

Despite the numerous models of the cell membrane proposed prior to the fluid mosaic model, it remains the primary archetype for the cell membrane long after its inception in the 1970s. [9] Although the fluid mosaic model has been modernized to detail contemporary discoveries, the basics have remained constant: the membrane is a lipid bilayer composed of hydrophilic exterior heads and a hydrophobic interior where proteins can interact with hydrophilic heads through polar interactions, but proteins that span the bilayer fully or partially have hydrophobic amino acids that interact with the non-polar lipid interior. The fluid mosaic model not only provided an accurate representation of membrane mechanics, it enhanced the study of hydrophobic forces, which would later develop into an essential descriptive limitation to describe biological macromolecules. [9]

For many centuries, the scientists cited disagreed with the significance of the structure they were seeing as the cell membrane. For almost two centuries, the membranes were seen but mostly disregarded as an important structure with cellular function. It was not until the 20th century that the significance of the cell membrane as it was acknowledged. Finally, two scientists Gorter and Grendel (1925) made the discovery that the membrane is "lipid-based". From this, they furthered the idea that this structure would have to be in a formation that mimicked layers. Once studied further, it was found by comparing the sum of the cell surfaces and the surfaces of the lipids, a 2:1 ratio was estimated; thus, providing the first basis of the bilayer structure known today. This discovery initiated many new studies that arose globally within various fields of scientific studies, confirming that the structure and functions of the cell membrane are widely accepted. [9]

The structure has been variously referred to by different writers as the ectoplast (de Vries, 1885), [14] Plasmahaut (plasma skin, Pfeffer, 1877, 1891), [15] Hautschicht (skin layer, Pfeffer, 1886; used with a different meaning by Hofmeister, 1867), plasmatic membrane (Pfeffer, 1900), [16] plasma membrane, cytoplasmic membrane, cell envelope and cell membrane. [17] [18] Some authors who did not believe that there was a functional permeable boundary at the surface of the cell preferred to use the term plasmalemma (coined by Mast, 1924) for the external region of the cell. [19] [20] [21]


Cell membranes contain a variety of biological molecules, notably lipids and proteins. Composition is not set, but constantly changing for fluidity and changes in the environment, even fluctuating during different stages of cell development. Specifically, the amount of cholesterol in human primary neuron cell membrane changes, and this change in composition affects fluidity throughout development stages. [22]

Material is incorporated into the membrane, or deleted from it, by a variety of mechanisms:


Examples of the major membrane phospholipids and glycolipids: phosphatidylcholine (PtdCho), phosphatidylethanolamine (PtdEtn), phosphatidylinositol (PtdIns), phosphatidylserine (PtdSer). Membrane Lipids.svg
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 sterols. The amount of each depends upon the type of cell, but in the majority of cases phospholipids are the most abundant, often contributing for over 50% of all lipids in plasma membranes. [23] [24] Glycolipids only account for a minute amount of about 2% and sterols make up the rest. In red blood cell studies, 30% of the plasma membrane is lipid. However, for the majority of eukaryotic cells, the composition of plasma membranes is about half lipids and half proteins by weight.

The fatty chains in phospholipids and glycolipids usually contain an even number of carbon atoms, typically between 16 and 20. 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 acid chains have a profound effect on membrane fluidity as unsaturated lipids create a kink, preventing the fatty acids from packing together as tightly, thus decreasing the melting temperature (increasing the fluidity) of the membrane. [23] [24] 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. Under physiological conditions phospholipid molecules in the cell membrane are in the liquid crystalline state. It means the lipid molecules are free to diffuse and exhibit rapid lateral diffusion along the layer in which they are present. [23] However, the exchange of phospholipid molecules between intracellular and extracellular leaflets of the bilayer is a very slow process. Lipid rafts and caveolae are examples of cholesterol-enriched microdomains in the cell membrane. [24] Also, a fraction of the lipid in direct contact with integral membrane proteins, which is tightly bound to the protein surface is called annular lipid shell; it behaves as a part of protein complex.

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. [4] Additionally, the amount of cholesterol in biological membranes varies between organisms, cell types, and even in individual cells. Cholesterol, a major component of animal plasma membranes, regulates the fluidity of the overall membrane, meaning that cholesterol controls the amount of movement of the various cell membrane components based on its concentrations. [4] In high temperatures, cholesterol inhibits the movement of phospholipid fatty acid chains, causing a reduced permeability to small molecules and reduced membrane fluidity. The opposite is true for the role of cholesterol in cooler temperatures. Cholesterol production, and thus concentration, is up-regulated (increased) in response to cold temperature. At cold temperatures, cholesterol interferes with fatty acid chain interactions. Acting as antifreeze, cholesterol maintains the fluidity of the membrane. Cholesterol is more abundant in cold-weather animals than warm-weather animals. In plants, which lack cholesterol, related compounds called sterols perform the same function as cholesterol. [4]

Phospholipids forming lipid vesicles

Lipid vesicles or liposomes are approximately spherical pockets that are enclosed by a lipid bilayer. [25] These structures are used in laboratories to study the effects of chemicals in cells by delivering these chemicals directly to the cell, as well as getting more insight into cell membrane permeability. Lipid vesicles and liposomes are formed by first suspending a lipid in an aqueous solution then agitating the mixture through sonication, resulting in a vesicle. By measuring the rate of efflux from that of the inside of the vesicle to the ambient solution, allows researcher to better understand membrane permeability. Vesicles can be formed with molecules and ions inside the vesicle by forming the vesicle with the desired molecule or ion present in the solution. Proteins can also be embedded into the membrane through solubilizing the desired proteins in the presence of detergents and attaching them to the phospholipids in which the liposome is formed. These provide researchers with a tool to examine various membrane protein functions.


Plasma membranes also contain carbohydrates, predominantly glycoproteins, but with some glycolipids (cerebrosides and gangliosides). Carbohydrates are important in the role of cell-cell recognition in eukaryotes; they are located on the surface of the cell where they recognize host cells and share information, viruses that bind to cells using these receptors cause an infection [26] For the most part, no glycosylation occurs on membranes within the cell; rather generally glycosylation occurs on the extracellular surface of the plasma membrane. The glycocalyx is an important feature in all cells, especially epithelia with microvilli. Recent data suggest the glycocalyx participates in cell adhesion, lymphocyte homing, [26] and many others. 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.


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 has large content of proteins, typically around 50% of membrane volume [27] These proteins are important for the cell because they are responsible for various biological activities. Approximately a third of the genes in yeast code specifically for them, and this number is even higher in multicellular organisms. [25] Membrane proteins consist of three main types: integral proteins, peripheral proteins, and lipid-anchored proteins. [4]

As shown in the adjacent table, integral proteins are amphipathic transmembrane proteins. Examples of integral proteins include ion channels, proton pumps, and g-protein coupled receptors. Ion channels allow inorganic ions such as sodium, potassium, calcium, or chlorine to diffuse down their electrochemical gradient across the lipid bilayer through hydrophilic pores across the membrane. The electrical behavior of cells (i.e. nerve cells) are controlled by ion channels. [4] Proton pumps are protein pumps that are embedded in the lipid bilayer that allow protons to travel through the membrane by transferring from one amino acid side chain to another. Processes such as electron transport and generating ATP use proton pumps. [4] A G-protein coupled receptor is a single polypeptide chain that crosses the lipid bilayer seven times responding to signal molecules (i.e. hormones and neurotransmitters). G-protein coupled receptors are used in processes such as cell to cell signaling, the regulation of the production of cAMP, and the regulation of ion channels. [4]

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, signaling, enzymatic activity, or transporting substances across the membrane.

Most membrane proteins must be inserted in some way into the membrane. [28] 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 are then transported to their final destination in vesicles, where the vesicle fuses with the target membrane.


A detailed diagram of the cell membrane Cell membrane detailed diagram en.svg
A detailed diagram of the cell membrane
Illustration depicting cellular diffusion Blausen 0213 CellularDiffusion.png
Illustration depicting cellular diffusion

The cell membrane surrounds the cytoplasm of living cells, physically separating the intracellular components from the extracellular environment. The cell membrane also plays a role in anchoring the cytoskeleton to provide shape to the cell, and in attaching to the extracellular matrix and other cells to hold them together to form tissues. Fungi, bacteria, most archaea, and plants also have a cell wall, which provides a mechanical support to the cell and precludes the passage of larger molecules.

The cell membrane 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 achieved by either passive transport, occurring without the input of cellular energy, or by active transport, requiring the cell to expend energy in transporting it. The membrane also maintains the cell potential. The cell membrane thus works as a selective filter that allows only certain things to come inside or go outside the cell. The cell employs a number of transport mechanisms that involve biological membranes:

1. Passive osmosis and diffusion: Some substances (small molecules, ions) such as carbon dioxide (CO2) and oxygen (O2), can move across the plasma membrane by diffusion, which is a passive transport process. Because the membrane acts as a barrier for certain molecules and ions, they can occur in different concentrations on the two sides of the membrane. Diffusion occurs when small molecules and ions move freely from high concentration to low concentration in order to equilibrate the membrane. It is considered a passive transport process because it does not require energy and is propelled by the concentration gradient created by each side of the membrane. [29] Such a concentration gradient across a semipermeable membrane sets up an osmotic flow for the water. Osmosis, in biological systems involves a solvent, moving through a semipermeable membrane similarly to passive diffusion as the solvent still moves with the concentration gradient and requires no energy. While water is the most common solvent in cell, it can also be other liquids as well as supercritical liquids and gases. [30]

2. Transmembrane protein channels and transporters: Transmembrane proteins extend through the lipid bilayer of the membranes; they function on both sides of the membrane to transport molecules across it. [31] Nutrients, such as sugars or amino acids, must enter the cell, and certain products of metabolism must leave the cell. Such molecules can diffuse passively through protein channels such as aquaporins in facilitated diffusion or are pumped across the membrane by transmembrane transporters. Protein channel proteins, also called permeases, are usually quite specific, and they only recognize and transport a limited variety of chemical substances, often limited to a single substance. Another example of a transmembrane protein is a cell-surface receptor, which allow cell signaling molecules to communicate between cells. [31]

3. Endocytosis: Endocytosis is the process in which cells absorb molecules by engulfing them. The plasma membrane creates a small deformation inward, called an invagination, in which the substance to be transported is captured. This invagination is caused by proteins on the outside on the cell membrane, acting as receptors and clustering into depressions that eventually promote accumulation of more proteins and lipids on the cytosolic side of the membrane. [32] The deformation then pinches off from the membrane on the inside of the cell, creating a vesicle containing the captured substance. Endocytosis is a pathway for internalizing solid particles ("cell eating" or phagocytosis), small molecules and ions ("cell drinking" or pinocytosis), and macromolecules. Endocytosis requires energy and is thus a form of active transport.

4. Exocytosis: Just as material can be brought into the cell by invagination and formation of a vesicle, the membrane of a vesicle can be fused with the plasma membrane, extruding its contents to the surrounding medium. This is the process of exocytosis. Exocytosis occurs in various cells to remove undigested residues of substances brought in by endocytosis, to secrete substances such as hormones and enzymes, and to transport a substance completely across a cellular barrier. In the process of exocytosis, the undigested waste-containing food vacuole or the secretory vesicle budded from Golgi apparatus, is first moved by cytoskeleton from the interior of the cell to the surface. The vesicle membrane comes in contact with the plasma membrane. The lipid molecules of the two bilayers rearrange themselves and the two membranes are, thus, fused. A passage is formed in the fused membrane and the vesicles discharges its contents outside the cell.


Prokaryotes are divided into two different groups, Archaea and Bacteria, with bacteria dividing further into gram-positive and gram-negative. Gram-negative bacteria have both a plasma membrane and an outer membrane separated by periplasm, however, other prokaryotes have only a plasma membrane. These two membranes differ in many aspects. The outer membrane of the gram-negative bacteria differ from other prokaryotes due to phospholipids forming the exterior of the bilayer, and lipoproteins and phospholipids forming the interior. [33] The outer membrane typically has a porous quality due to its presence of membrane proteins, such as gram-negative porins, which are pore-forming proteins. The inner, plasma membrane is also generally symmetric whereas the outer membrane is asymmetric because of proteins such as the aforementioned. Also, for the prokaryotic membranes, there are multiple things that can affect the fluidity. One of the major factors that can affect the fluidity is fatty acid composition. For example, when the bacteria Staphylococcus aureus was grown in 37C for 24h, the membrane exhibited a more fluid state instead of a gel-like state. This supports the concept that in higher temperatures, the membrane is more fluid than in colder temperatures. When the membrane is becoming more fluid and needs to become more stabilized, it will make longer fatty acid chains or saturated fatty acid chains in order to help stabilize the membrane. [34] Bacteria are also surrounded by a cell wall composed of peptidoglycan (amino acids and sugars). Some eukaryotic cells also have cell walls, but none that are made of peptidoglycan. The outer membrane of gram negative bacteria is rich in lipopolysaccharides, which are combined poly- or oligosaccharide and carbohydrate lipid regions that stimulate the cell's natural immunity. [35] The outer membrane can bleb out into periplasmic protrusions under stress conditions or upon virulence requirements while encountering a host target cell, and thus such blebs may work as virulence organelles. [36] Bacterial cells provide numerous examples of the diverse ways in which prokaryotic cell membranes are adapted with structures that suit the organism's niche. For example, proteins on the surface of certain bacterial cells aid in their gliding motion. [37] Many gram-negative bacteria have cell membranes which contain ATP-driven protein exporting systems. [37]


Fluid mosaic model

According to the fluid mosaic model of S. J. Singer and G. L. Nicolson (1972), which replaced the earlier model of Davson and Danielli, biological membranes can be considered as a two-dimensional liquid in which lipid and protein molecules diffuse more or less easily. [38] Although the lipid bilayers that form the basis of the membranes do indeed form two-dimensional liquids by themselves, the plasma membrane also contains a large quantity of proteins, which provide more structure. Examples of such structures are protein-protein complexes, pickets and fences formed by the actin-based cytoskeleton, and potentially lipid rafts.

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. Fluid Mosaic.svg
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.

Lipid bilayers form through the process of self-assembly. The cell membrane consists primarily of a thin layer of amphipathic phospholipids that spontaneously arrange so that the hydrophobic "tail" regions are isolated from the surrounding water while the hydrophilic "head" regions interact with the intracellular (cytosolic) and extracellular faces of the resulting bilayer. This forms a continuous, spherical lipid bilayer. Hydrophobic interactions (also known as the hydrophobic effect) are the major driving forces in the formation of lipid bilayers. An increase in interactions between hydrophobic molecules (causing clustering of hydrophobic regions) allows water molecules to bond more freely with each other, increasing the entropy of the system. This complex interaction can include noncovalent interactions such as van der Waals, electrostatic and hydrogen bonds.

Lipid bilayers are generally impermeable to ions and polar molecules. The arrangement of hydrophilic heads and hydrophobic tails of the lipid bilayer prevent polar solutes (ex. 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, channels and gates. 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 moieties moving through the membrane.

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. [39]

Membrane polarity

Alpha intercalated cell Alpha Intercalated Cell Cartoon.svg
Alpha intercalated cell

The apical membrane or luminal membrane of a polarized cell is the surface of the plasma membrane that faces inward to the lumen. This is particularly evident in epithelial and endothelial cells, but also describes other polarized cells, such as neurons. The basolateral membrane of a polarized cell is the surface of the plasma membrane that forms its basal and lateral surfaces. It faces outwards, towards the interstitium, and away from the lumen. Basolateral membrane is a compound phrase referring to the terms "basal (base) membrane" and "lateral (side) membrane", which, especially in epithelial cells, are identical in composition and activity. Proteins (such as ion channels and pumps) are free to move from the basal to the lateral surface of the cell or vice versa in accordance with the fluid mosaic model. Tight junctions join epithelial cells near their apical surface to prevent the migration of proteins from the basolateral membrane to the apical membrane. The basal and lateral surfaces thus remain roughly equivalent[ clarification needed ] to one another, yet distinct from the apical surface.

Membrane structures

Diagram of the Cell Membrane's structures. Cell membrane drawing-en.svg
Diagram of the Cell Membrane's structures.

Cell membrane can form different types of "supramembrane" structures such as caveola, postsynaptic density, podosome, invadopodium, focal adhesion, and different types of cell junctions. These structures are usually responsible for cell adhesion, communication, endocytosis and exocytosis. They can be visualized by electron microscopy or fluorescence microscopy. They are composed of specific proteins, such as integrins and cadherins.


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. Indeed, cytoskeletal elements interact extensively and intimately with the cell membrane. [40] 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 microtubule-based extensions covered by the cell membrane, and filopodia, which are actin-based extensions. These extensions are ensheathed in membrane and project from the surface of the cell in order to sense the external environment and/or make contact with the substrate or other cells. The apical surfaces of epithelial cells are dense with actin-based finger-like projections known as microvilli, which increase cell surface area and thereby increase the absorption rate of nutrients. Localized decoupling of the cytoskeleton and cell membrane results in formation of a bleb.

Intracellular membranes

The content of the cell, inside the cell membrane, is composed of numerous membrane-bound organelles, which contribute to the overall function of the cell. The origin, structure, and function of each organelle leads to a large variation in the cell composition due to the individual uniqueness associated with each organelle.


The cell membrane has different lipid and protein compositions in distinct types of cells and may have therefore specific names for certain cell types.


The permeability of a membrane is the rate of passive diffusion of molecules through the membrane. These molecules are known as permeant molecules. Permeability depends mainly on the electric charge and polarity of the molecule and to a lesser extent the molar mass of the molecule. Due to the cell membrane's hydrophobic nature, small electrically neutral molecules pass through the membrane more easily than charged, large ones. The inability of charged molecules to pass through the cell membrane results in pH partition of substances throughout the fluid compartments of the body.

See also

Notes and references

  1. Kimball's Biology pages Archived 2009-01-25 at the Wayback Machine , Cell Membranes
  2. Singleton P (1999). Bacteria in Biology, Biotechnology and Medicine (5th ed.). New York: Wiley. ISBN   978-0-471-98880-9.
  3. Tom Herrmann; Sandeep Sharma (March 2, 2019). "Physiology, Membrane". StatPearls. 1 SIU School of Medicine 2 Baptist Regional Medical Center. PMID   30855799.{{cite journal}}: CS1 maint: location (link)
  4. 1 2 3 4 5 6 7 8 Alberts B, Johnson A, Lewis J, et al. (2002). Molecular Biology of the Cell (4th ed.). New York: Garland Science. ISBN   978-0-8153-3218-3. Archived from the original on 2017-12-20.
  5. Budin I, Devaraj NK (January 2012). "Membrane assembly driven by a biomimetic coupling reaction". Journal of the American Chemical Society. 134 (2): 751–3. doi:10.1021/ja2076873. PMC   3262119 . PMID   22239722.
  6. Staff (January 25, 2012). "Chemists Synthesize Artificial Cell Membrane". ScienceDaily. Archived from the original on January 29, 2012. Retrieved February 18, 2012.
  7. Staff (January 26, 2012). "Chemists create artificial cell membrane". kurzweilai.net. Archived from the original on January 28, 2012. Retrieved February 18, 2012.
  8. Zeidi, Mahdi; Kim, Chun IL (2018). "The effects of intra-membrane viscosity on lipid membrane morphology: complete analytical solution". Scientific Reports. 8 (1): 12845. Bibcode:2018NatSR...812845Z. doi: 10.1038/s41598-018-31251-6 . ISSN   2045-2322. PMC   6110749 . PMID   30150612.
  9. 1 2 3 4 5 6 7 Lombard J (December 2014). "Once upon a time the cell membranes: 175 years of cell boundary research". Biology Direct. 9: 32. doi:10.1186/s13062-014-0032-7. PMC   4304622 . PMID   25522740.
  10. Leray, C. Chronological history of lipid center. Cyberlipid Center. Last updated on 11 November 2017. link Archived 2017-10-13 at the Wayback Machine .
  11. Gorter E, Grendel F (March 1925). "On Bimolecular Layers of Lipoids on the Chromocytes of the Blood". The Journal of Experimental Medicine. 41 (4): 439–43. doi:10.1084/jem.41.4.439. PMC   2130960 . PMID   19868999.
  12. Karp, Gerald (2009). Cell and Molecular Biology (6th ed.). USA: John Wiley & Sons, Inc. p. 120. ISBN   9780470483374.
  13. S J Singer and G L Nicolson."The fluid mosaic model of the structure of cell membranes." Science. (1972) 175. 720-731.
  14. de Vries H (1885). "Plasmolytische Studien über die Wand der Vakuolen". Jahrb. Wiss. Bot. 16: 465–598.
  15. Pfeffer, W. 1877. Osmotische Untersuchungen: Studien zur Zell Mechanik. Engelmann, Leipzig.
  16. Pfeffer, W., 1900–1906. The Physiology of Plants, Archived 2018-06-02 at the Wayback Machine . Translated by A. J. Ewart from the 2nd German ed. of Pflanzenphysiologie, 1897-1904, Archived 2018-06-01 at the Wayback Machine . Clarendon Press, Oxford.
  17. Sharp, L. W. (1921). Introduction To Cytology . New York: McGraw Hill, p. 42.
  18. Kleinzeller, A. 1999. Charles Ernest Overton's concept of a cell membrane. In: Membrane permeability: 100 years since Ernest Overton (ed. Deamer D.W., Kleinzeller A., Fambrough D.M.), pp. 1–18, Academic Press, San Diego, .
  19. Mast SO (1924). "Structure and locomotion in Amoeba proteus". Anat. Rec. 29 (2): 88. doi: 10.1002/ar.1090290205 .
  20. Plowe JQ (1931). "Membranes in the plant cell. I. Morphological membranes at protoplasmic surfaces". Protoplasma. 12: 196–220. doi:10.1007/BF01618716. S2CID   32248784.
  21. Wayne R (2009). Plant Cell Biology: From Astronomy to Zoology. Amsterdam: Elsevier/Academic Press. p. 17. ISBN   9780080921273.
  22. Noutsi P, Gratton E, Chaieb S (2016-06-30). "Assessment of Membrane Fluidity Fluctuations during Cellular Development Reveals Time and Cell Type Specificity". PLOS ONE. 11 (6): e0158313. Bibcode:2016PLoSO..1158313N. doi: 10.1371/journal.pone.0158313 . PMC   4928918 . PMID   27362860.
  23. 1 2 3 Lodish H, Berk A, Zipursky LS, et al. (2000). "Biomembranes: Structural Organization and Basic Functions". Molecular Cell Biology (4th ed.). New York: Scientific American Books. ISBN   978-0-7167-3136-8.
  24. 1 2 3 Cooper GM (2000). "Structure of the Plasma Membrane". The Cell: A Molecular Approach (2nd ed.). Archived from the original on 2017-09-19.
  25. 1 2 Lodish H, Berk A, Zipursky SL, Matsudaira P, Baltimore D, Darnell J (2000). "Biomembranes: Structural Organization and Basic Functions". Molecular Cell Biology (4th ed.). Archived from the original on 2018-06-05.
  26. 1 2 Brandley BK, Schnaar RL (July 1986). "Cell-surface carbohydrates in cell recognition and response". Journal of Leukocyte Biology. 40 (1): 97–111. doi:10.1002/jlb.40.1.97. PMID   3011937. S2CID   45528175.
  27. Jesse Gray; Shana Groeschler; Tony Le; Zara Gonzalez (2002). "Membrane Structure" (SWF). Davidson College. Archived from the original on 2007-01-08. Retrieved 2007-01-11.
  28. Lodish H, Berk A, Zipursky SL, Matsudaira P, Baltimore D, Darnell J (2000). "Post-Translational Modifications and Quality Control in the Rough ER". Molecular Cell Biology (4th ed.).
  29. Cooper, Geoffrey M. (2000). "Transport of Small Molecules". The Cell: A Molecular Approach (2nd ed.). Archived from the original on 2018-06-05.
  30. Kramer EM, Myers DR (April 2013). "Osmosis is not driven by water dilution". Trends in Plant Science. 18 (4): 195–7. doi:10.1016/j.tplants.2012.12.001. PMID   23298880.
  31. 1 2 Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P (2002). "Membrane Proteins". Molecular Biology of the Cell (4th ed.). Archived from the original on 2018-06-05.
  32. Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P (2002). "Transport into the Cell from the Plasma Membrane: Endocytosis". Molecular Biology of the Cell (4th ed.). Garland Science. Archived from the original on 2018-06-05.
  33. Salton MR, Kim K (1996). Baron S (ed.). Medical Microbiology (4th ed.). Galveston (TX): University of Texas Medical Branch at Galveston. ISBN   978-0963117212. PMID   21413343.
  34. Mishra NN, Liu GY, Yeaman MR, Nast CC, Proctor RA, McKinnell J, Bayer AS (February 2011). "Carotenoid-related alteration of cell membrane fluidity impacts Staphylococcus aureus susceptibility to host defense peptides". Antimicrobial Agents and Chemotherapy. 55 (2): 526–31. doi:10.1128/AAC.00680-10. PMC   3028772 . PMID   21115796.
  35. Alexander C, Rietschel ET (2001). "Bacterial lipopolysaccharides and innate immunity". Journal of Endotoxin Research. 7 (3): 167–202. doi: 10.1177/09680519010070030101 . PMID   11581570. S2CID   86224757.
  36. YashRoy RC (1999). "A structural model for virulence organellae of gram negative organisms with reference to Salmonella pathogenicity in chicken ileum". Indian Journal of Poultry Science. 34 (2): 213–219. Archived from the original on 2014-11-07.
  37. 1 2 Saier MH (2013). "Microcompartments and protein machines in prokaryotes". Journal of Molecular Microbiology and Biotechnology. 23 (4–5): 243–69. doi:10.1159/000351625. PMC   3832201 . PMID   23920489.
  38. Singer SJ, Nicolson GL (February 1972). "The fluid mosaic model of the structure of cell membranes". Science. 175 (4023): 720–31. Bibcode:1972Sci...175..720S. doi:10.1126/science.175.4023.720. PMID   4333397. S2CID   83851531.
  39. Zeidi, Mahdi; Kim, Chun IL (2018). "The effects of intra-membrane viscosity on lipid membrane morphology: complete analytical solution". Scientific Reports. 8 (1): 12845. Bibcode:2018NatSR...812845Z. doi: 10.1038/s41598-018-31251-6 . ISSN   2045-2322. PMC   6110749 . PMID   30150612.
  40. Doherty GJ, McMahon HT (2008). "Mediation, modulation, and consequences of membrane-cytoskeleton interactions". Annual Review of Biophysics. 37: 65–95. doi:10.1146/annurev.biophys.37.032807.125912. PMID   18573073. S2CID   17352662.
  41. Whatley JM, John P, Whatley FR (April 1979). "From extracellular to intracellular: the establishment of mitochondria and chloroplasts". Proceedings of the Royal Society of London. Series B, Biological Sciences. 204 (1155): 165–87. Bibcode:1979RSPSB.204..165W. doi:10.1098/rspb.1979.0020. PMID   36620. S2CID   42398067.
  42. Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P (2002). "The Structure and Function of DNA". Molecular Biology of the Cell (4th ed.). Garland Science.
  43. Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walter P (2002). "The Transport of Molecules between the Nucleus and the Cytosol". Molecular Biology of the Cell (4th ed.). Garland Science.
  44. Cooper GM (2000). "The Endoplasmic Reticulum". The Cell: A Molecular Approach (2nd ed.). Archived from the original on 2017-10-03.
  45. Xu H, Su W, Cai M, Jiang J, Zeng X, Wang H (2013-04-16). "The asymmetrical structure of Golgi apparatus membranes revealed by in situ atomic force microscope". PLOS ONE. 8 (4): e61596. Bibcode:2013PLoSO...861596X. doi: 10.1371/journal.pone.0061596 . PMC   3628984 . PMID   23613878.
  46. 1 2 Reed R, Wouston TW, Todd PM (July 1966). "Structure and function of the sarcolemma of skeletal muscle". Nature. 211 (5048): 534–6. Bibcode:1966Natur.211..534R. doi:10.1038/211534b0. PMID   5967498. S2CID   4183025.
  47. Campbell KP, Stull JT (April 2003). "Skeletal muscle basement membrane-sarcolemma-cytoskeleton interaction minireview series". The Journal of Biological Chemistry. 278 (15): 12599–600. doi: 10.1074/jbc.r300005200 . PMID   12556456.
  48. Mitra K, Ubarretxena-Belandia I, Taguchi T, Warren G, Engelman DM (March 2004). "Modulation of the bilayer thickness of exocytic pathway membranes by membrane proteins rather than cholesterol". Proceedings of the National Academy of Sciences of the United States of America. 101 (12): 4083–8. Bibcode:2004PNAS..101.4083M. doi: 10.1073/pnas.0307332101 . PMC   384699 . PMID   15016920.
  49. Wessel GM, Wong JL (October 2009). "Cell surface changes in the egg at fertilization". Molecular Reproduction and Development. 76 (10): 942–53. doi:10.1002/mrd.21090. PMC   2842880 . PMID   19658159.
  50. Raine CS (1999). "Characteristics of the Neuron". Basic Neurochemistry: Molecular, Cellular and Medical Aspects (6th ed.).
  51. Fitzpatrick MO, Maxwell WL, Graham DI (March 1998). "The role of the axolemma in the initiation of traumatically induced axonal injury". Journal of Neurology, Neurosurgery, and Psychiatry. 64 (3): 285–7. doi:10.1136/jnnp.64.3.285. PMC   2169978 . PMID   9527135.

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<span class="mw-page-title-main">Biological membrane</span> Enclosing or separating membrane in organisms acting as selective semi-permeable barrier

A biological membrane, biomembrane or cell membrane is a selectively permeable membrane that separates the interior of a cell from the external environment or creates intracellular compartments by serving as a boundary between one part of the cell and another. Biological membranes, in the form of eukaryotic cell membranes, consist of a phospholipid bilayer with embedded, integral and peripheral proteins used in communication and transportation of chemicals and ions. The bulk of lipids in a cell membrane provides a fluid matrix for proteins to rotate and laterally diffuse for physiological functioning. Proteins are adapted to high membrane fluidity environment of the lipid bilayer with the presence of an annular lipid shell, consisting of lipid molecules bound tightly to the surface of integral membrane proteins. The cell membranes are different from the isolating tissues formed by layers of cells, such as mucous membranes, basement membranes, and serous membranes.

<span class="mw-page-title-main">Endomembrane system</span> Membranes in the cytoplasm of a eukaryotic cell

The endomembrane system is composed of the different membranes (endomembranes) that are suspended in the cytoplasm within a eukaryotic cell. These membranes divide the cell into functional and structural compartments, or organelles. In eukaryotes the organelles of the endomembrane system include: the nuclear membrane, the endoplasmic reticulum, the Golgi apparatus, lysosomes, vesicles, endosomes, and plasma (cell) membrane among others. The system is defined more accurately as the set of membranes that forms a single functional and developmental unit, either being connected directly, or exchanging material through vesicle transport. Importantly, the endomembrane system does not include the membranes of plastids or mitochondria, but might have evolved partially from the actions of the latter.

<span class="mw-page-title-main">Phospholipid</span> Class of lipids

Phospholipids are a class of lipids whose molecule has a hydrophilic "head" containing a phosphate group and two hydrophobic "tails" derived from fatty acids, joined by an alcohol residue. Marine phospholipids typically have omega-3 fatty acids EPA and DHA integrated as part of the phospholipid molecule. The phosphate group can be modified with simple organic molecules such as choline, ethanolamine or serine.

<span class="mw-page-title-main">Vesicle (biology and chemistry)</span> Any small, fluid-filled, spherical organelle enclosed by a membrane

In cell biology, a vesicle is a structure within or outside a cell, consisting of liquid or cytoplasm enclosed by a lipid bilayer. Vesicles form naturally during the processes of secretion (exocytosis), uptake (endocytosis) and transport of materials within the plasma membrane. Alternatively, they may be prepared artificially, in which case they are called liposomes. If there is only one phospholipid bilayer, the vesicles are called unilamellar liposomes; otherwise they are called multilamellar liposomes. The membrane enclosing the vesicle is also a lamellar phase, similar to that of the plasma membrane, and intracellular vesicles can fuse with the plasma membrane to release their contents outside the cell. Vesicles can also fuse with other organelles within the cell. A vesicle released from the cell is known as an extracellular vesicle.

A transmembrane domain (TMD) is a membrane-spanning protein domain. TMDs generally adopt an alpha helix topological conformation, although some TMDs such as those in porins can adopt a different conformation. Because the interior of the lipid bilayer is hydrophobic, the amino acid residues in TMDs are often hydrophobic, although proteins such as membrane pumps and ion channels can contain polar residues. TMDs vary greatly in length, sequence, and hydrophobicity, adopting organelle-specific properties.

<span class="mw-page-title-main">Lipid bilayer</span> Membrane of two layers of lipid molecules

The lipid bilayer is a thin polar membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around all cells. The cell membranes of almost all organisms and many viruses are made of a lipid bilayer, as are the nuclear membrane surrounding the cell nucleus, and membranes of the membrane-bound organelles in the cell. The lipid bilayer is the barrier that keeps ions, proteins and other molecules where they are needed and prevents them from diffusing into areas where they should not be. Lipid bilayers are ideally suited to this role, even though they are only a few nanometers in width, because they are impermeable to most water-soluble (hydrophilic) molecules. Bilayers are particularly impermeable to ions, which allows cells to regulate salt concentrations and pH by transporting ions across their membranes using proteins called ion pumps.

<span class="mw-page-title-main">Semipermeable membrane</span> Membrane which will allow certain molecules or ions to pass through it by diffusion

Semipermeable membrane is a type of biological or synthetic, polymeric membrane that will allow certain molecules or ions to pass through it by osmosis. The rate of passage depends on the pressure, concentration, and temperature of the molecules or solutes on either side, as well as the permeability of the membrane to each solute. Depending on the membrane and the solute, permeability may depend on solute size, solubility, properties, or chemistry. How the membrane is constructed to be selective in its permeability will determine the rate and the permeability. Many natural and synthetic materials which are rather thick are also semipermeable. One example of this is the thin film on the inside of the egg.

<span class="mw-page-title-main">Fluid mosaic model</span> Describe the fluid mosaic model of plasma membrane

The fluid mosaic model explains various observations regarding the structure of functional cell membranes. According to this biological model, there is a lipid bilayer in which protein molecules are embedded. The phospholipid bilayer gives fluidity and elasticity to the membrane. Small amounts of carbohydrates are also found in the cell membrane. The biological model, which was devised by Seymour Jonathan Singer and Garth L. Nicolson in 2023, describes the cell membrane as a two-dimensional liquid that restricts the lateral diffusion of membrane components. Such domains are defined by the existence of regions within the membrane with special lipid and protein cocoon that promote the formation of lipid rafts or protein and glycoprotein complexes. In addition, it came before the other model that introduced the first bilayer. Another way to define membrane domains is the association of the lipid membrane with the cytoskeleton filaments and the extracellular matrix through membrane proteins. The current model describes important features relevant to many cellular processes, including: cell-cell signaling, apoptosis, cell division, membrane budding, and cell fusion. The fluid mosaic model is the most acceptable model of the plasma membrane. Its main function is to separate the contents of the cell from the exterior.

<span class="mw-page-title-main">Glycerophospholipid</span> Class of lipids

Glycerophospholipids or phosphoglycerides are glycerol-based phospholipids. They are the main component of biological membranes. Two major classes are known: those for bacteria and eukaryotes and a separate family for archaea.

<span class="mw-page-title-main">Endoplasm</span> Also known as entoplasm

Endoplasm generally refers to the inner, dense part of a cell's cytoplasm. This is opposed to the ectoplasm which is the outer (non-granulated) layer of the cytoplasm, which is typically watery and immediately adjacent to the plasma membrane. The nucleus is separated from the endoplasm by the nuclear envelope. The different makeups/viscosities of the endoplasm and ectoplasm contribute to the amoeba's locomotion through the formation of a pseudopod. However, other types of cells have cytoplasm divided into endo- and ectoplasm. The endoplasm, along with its granules, contains water, nucleic acids, amino acids, carbohydrates, inorganic ions, lipids, enzymes, and other molecular compounds. It is the site of most cellular processes as it houses the organelles that make up the endomembrane system, as well as those that stand alone. The endoplasm is necessary for most metabolic activities, including cell division.

The Davson–Danielli model was a model of the plasma membrane of a cell, proposed in 1935 by Hugh Davson and James Danielli. The model describes a phospholipid bilayer that lies between two layers of globular proteins, which is both trilaminar and lipoprotinious. The phospholipid bilayer had already been proposed by Gorter and Grendel in 1925; however, the flanking proteinaceous layers in the Davson–Danielli model were novel and intended to explain Danielli's observations on the surface tension of lipid bi-layers.

The bacterium, despite its simplicity, contains a well-developed cell structure which is responsible for some of its unique biological structures and pathogenicity. Many structural features are unique to bacteria and are not found among archaea or eukaryotes. Because of the simplicity of bacteria relative to larger organisms and the ease with which they can be manipulated experimentally, the cell structure of bacteria has been well studied, revealing many biochemical principles that have been subsequently applied to other organisms.

<span class="mw-page-title-main">Surfactin</span> Chemical compound

Surfactin is a cyclic lipopeptide, commonly used as an antibiotic for its capacity as a surfactant. It is an amphiphile capable of withstanding hydrophilic and hydrophobic environments. The Gram-positive bacterial species Bacillus subtilis produces surfactin for its antibiotic effects against competitors. Surfactin showcases antibacterial, antiviral, antifungal, and hemolytic effects.

In biology, membrane fluidity refers to the viscosity of the lipid bilayer of a cell membrane or a synthetic lipid membrane. Lipid packing can influence the fluidity of the membrane. Viscosity of the membrane can affect the rotation and diffusion of proteins and other bio-molecules within the membrane, there-by affecting the functions of these things.

<span class="mw-page-title-main">Membrane lipid</span> Lipid molecules on cell membrane

Membrane lipids are a group of compounds which form the double-layered surface of all cells. The three major classes of membrane lipids are phospholipids, glycolipids, and cholesterol. Lipids are amphiphilic: they have one end that is soluble in water ('polar') and an ending that is soluble in fat ('nonpolar'). By forming a double layer with the polar ends pointing outwards and the nonpolar ends pointing inwards membrane lipids can form a 'lipid bilayer' which keeps the watery interior of the cell separate from the watery exterior. The arrangements of lipids and various proteins, acting as receptors and channel pores in the membrane, control the entry and exit of other molecules and ions as part of the cell's metabolism. In order to perform physiological functions, membrane proteins are facilitated to rotate and diffuse laterally in two dimensional expanse of lipid bilayer by the presence of a shell of lipids closely attached to protein surface, called annular lipid shell.

<span class="mw-page-title-main">Outline of cell biology</span> Overview of and topical guide to cell biology

The following outline is provided as an overview of and topical guide to cell biology:

<span class="mw-page-title-main">History of cell membrane theory</span>

Cell theory has its origins in seventeenth century. microscopy observations, but it was nearly two hundred years before a complete cell membrane theory was developed to explain what separates cells from the outside world. By the 19th century it was accepted that some form of semi-permeable barrier must exist around a cell. Studies of the action of anesthetic molecules led to the theory that this barrier might be made of some sort of fat (lipid), but the structure was still unknown. A series of pioneering experiments in 1925 indicated that this barrier membrane consisted of two molecular layers of lipids—a lipid bilayer. New tools over the next few decades confirmed this theory, but controversy remained regarding the role of proteins in the cell membrane. Eventually the fluid mosaic model was composed in which proteins “float” in a fluid lipid bilayer "sea". Although simplistic and incomplete, this model is still widely referenced today.

<span class="mw-page-title-main">Ethanol-induced non-lamellar phases in phospholipids</span>

The presence of ethanol can lead to the formations of non-lamellar phases also known as non-bilayer phases. Ethanol has been recognized as being an excellent solvent in an aqueous solution for inducing non-lamellar phases in phospholipids. The formation of non-lamellar phases in phospholipids is not completely understood, but it is significant that this amphiphilic molecule is capable of doing so. The formation of non-lamellar phases is significant in biomedical studies which include drug delivery, the transport of polar and non-polar ions using solvents capable of penetrating the biomembrane, increasing the elasticity of the biomembrane when it is being disrupted by unwanted substances and functioning as a channel or transporter of biomaterial.

<span class="mw-page-title-main">Intracellular transport</span> Directed movement of vesicles and substances within a cell

Intracellular transport is the movement of vesicles and substances within a cell. Intracellular transport is required for maintaining homeostasis within the cell by responding to physiological signals. Proteins synthesized in the cytosol are distributed to their respective organelles, according to their specific amino acid’s sorting sequence. Eukaryotic cells transport packets of components to particular intracellular locations by attaching them to molecular motors that haul them along microtubules and actin filaments. Since intracellular transport heavily relies on microtubules for movement, the components of the cytoskeleton play a vital role in trafficking vesicles between organelles and the plasma membrane by providing mechanical support. Through this pathway, it is possible to facilitate the movement of essential molecules such as membrane‐bounded vesicles and organelles, mRNA, and chromosomes.

This glossary of cell biology is a list of definitions of terms and concepts commonly used in the study of cell biology and related disciplines in biology, including developmental biology, genetics, microbiology, molecular biology, and biochemistry.