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Phospholipids [1] 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 (usually a glycerol molecule). Marine phospholipids typically have omega-3 fatty acids EPA and DHA integrated as part of the phospholipid molecule. [2]
The lipid bilayer (or phospholipid 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 ...
The phospholipid bilayer is a two-layer structure mainly composed of phospholipids, which are amphiphilic molecules that have hydrophilic and hydrophobic regions. [2] The hydrophilic region contains the polar head group. This region is exposed to aqueous substances located mainly in the exterior portion of the biomembrane.
Phospholipid bilayer. Each phospholipid consists of a polar hydrophilic head (red) and two hydrophobic fatty acid tails. The fatty acid structure affects the bilayer structure. Fatty acids with an unsaturated tail (blue) disrupt the packing of those with only saturated tails (black).
Each glycerophospholipid molecule consists of a small polar head group and two long hydrophobic chains. In the cell membrane, the two layers of phospholipids are arranged as follows: the hydrophobic tails point to each other and form a fatty, hydrophobic center; the ionic head groups are placed at the inner and outer surfaces of the cell membrane
The best known sterol is cholesterol, which is found in humans. Cholesterol also occurs naturally in other eukaryote cell membranes. Sterols have a hydrophobic four-membered fused ring rigid structure, and a small polar head group. Cholesterol is bio-synthesised from mevalonate via a squalene cyclisation of terpenoids.
The hydrophobic inner core region of typical biological membranes may have a thickness of around 27 to 32 Å, as estimated by Small angle X-ray scattering (SAXS). [8] The boundary region between the hydrophobic inner core and the hydrophilic interfacial regions is very narrow, at around 3 Å, (see lipid bilayer article for a description of its ...
[2]: 333–4 This is known as the hydrophobic effect. In an aqueous system, the polar heads of lipids align towards the polar, aqueous environment, while the hydrophobic tails minimize their contact with water and tend to cluster together, forming a vesicle ; depending on the concentration of the lipid, this biophysical interaction may result ...