PLASMA MEMBRANE STRUCTURE PDF!
The plasma membrane provides structural support to the cell. It tethers the cytoskeleton, which is a network of protein filaments inside the cell that hold all the Functions of the Plasma · Plasma Membrane Structure. In this lesson, you will learn about the plasma membrane of. plasma membrane of a cell to gain an understanding of its structure and function. Structure of the Plasma Membrane. Like all other cellular membranes, the plasma membrane consists of both lipids and proteins. The fundamental structure of the membrane is the phospholipid bilayer, which forms a stable barrier between two aqueous compartments.
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Intwo Dutch scientists E. Grendel extracted plasma membrane structure membrane lipids from a known number of red blood cells, corresponding to a known surface area of plasma membrane.
They then determined the surface area occupied by a monolayer of the extracted lipid spread out at an air-water interface.
Plasma Membrane of a Cell: Definition, Function & Structure
The surface area of the lipid monolayer turned out to be twice that occupied by the erythrocyte plasma membranes, leading to the conclusion that the membranes consisted of lipid bilayers rather than monolayers.
The bilayer structure of the erythrocyte plasma membrane is clearly evident in high-magnification electron micrographs Figure This image results from the binding of the electron-dense plasma membrane structure metals used as stains in transmission electron microscopy see Chapter 1 to the polar head groups of the phospholipidswhich therefore appear as dark lines.
These dense lines are separated by the lightly stained interior portion of the membrane, which contains the hydrophobic fatty acid chains. Electron micrograph of a human red blood cell.
Structure of the plasma membrane (article) | Khan Academy
Note the railroad track appearance of the plasma membrane. As discussed in Chapter 2, the plasma membranes of animal cells contain four major phospholipids phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and sphingomyelinwhich together account for more than half of the lipid in most membranes.
These phospholipids are asymmetrically distributed between the two halves of the membrane bilayer Figure The outer leaflet of the plasma membrane consists mainly of phosphatidylcholine and sphingomyelinwhereas phosphatidylethanolamine and phosphatidylserine are the predominant phospholipids of the inner leaflet.
A fifth phospholipid, phosphatidylinositol, is also localized to the inner half of the plasma membrane structure membrane. Although phosphatidylinositol is a quantitatively minor membrane component, it plays an important role in cell signaling, as discussed in the next chapter.
The head groups of both phosphatidylserine and phosphatidylinositol plasma membrane structure negatively charged, so their predominance in the inner leaflet results in a net negative charge on the cytosolic face of the plasma membrane.
Plasma Membrane of a Cell: Definition, Function & Structure - Video & Lesson Transcript |
The outer leaflet consists predominantly of phosphatidylcholine, sphingomyelin, and glycolipids, whereas the inner leaflet contains phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol.
In addition to the phospholipidsthe plasma membranes of animal cells contain glycolipids and cholesterol. The glycolipids are found exclusively plasma membrane structure the outer leaflet of the plasma membranewith their carbohydrate portions exposed on the cell surface.
Cholesterol, on the other hand, is a major membrane constituent of animal cells, being present in about the same molar amounts as the phospholipids.
Two general features of phospholipid bilayers are critical to membrane function. First, the structure of phospholipids is responsible for the basic function of membranes as barriers between two aqueous compartments.
Because the interior of the phospholipid bilayer plasma membrane structure occupied by hydrophobic fatty acid chains, the membrane is impermeable to water-soluble molecules, including ions and most biological molecules. Second, bilayers of the naturally occurring phospholipids are viscous fluids, not solids.
The fatty acids of most natural phospholipids have one or more double bonds, which introduce kinks into the hydrocarbon chains plasma membrane structure make them difficult to pack together.
The long hydrocarbon chains of the fatty acids therefore move freely in the interior of the membrane, so the membrane itself is soft and flexible.
In addition, both phospholipids plasma membrane structure proteins are free to diffuse laterally within the membrane—a property that is critical for many membrane functions. Because of its rigid ring structure, cholesterol plays a distinct role in membrane structure.
Cholesterol will not form a membrane by itself, but inserts into a bilayer of phospholipids with its polar hydroxyl group close to the phospholipid head groups see Figure plasma membrane structure Depending on the temperature, cholesterol has distinct effects on membrane fluidity. At high temperatures, cholesterol interferes with the movement of the phospholipid fatty acid chains, making plasma membrane structure outer part of the membrane less fluid and reducing its permeability to small molecules.
Cell membrane can form different types of "supramembrane" structures such as caveolapostsynaptic densitypodosomeinvadopodiumfocal adhesionand different types of cell junctions.
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