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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]
As discussed in the Structure and organization section, the hydrophobic attraction of lipid tails in water is the primary force holding lipid bilayers together. Thus, the elastic modulus of the bilayer is primarily determined by how much extra area is exposed to water when the lipid molecules are stretched apart. [ 81 ]
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
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).
1-Oleoyl-2-palmitoyl-phosphatidylcholine. Phosphatidylcholines (PC) are a class of phospholipids that incorporate choline as a headgroup.They are a major component of biological membranes and can easily be obtained from a variety of readily available sources, such as egg yolk or soybeans, from which they are mechanically or chemically extracted using hexane.
Phosphatidylserine (PS) is the major acidic phospholipid class that accounts for 13–15% of the phospholipids in the human cerebral cortex. [7] In the plasma membrane, PS is localized exclusively in the cytoplasmic leaflet where it forms part of protein docking sites necessary for the activation of several key signaling pathways.
The phospholipid amphiphiles are the major structural component of cell membranes. Amphiphiles are the basis for a number of areas of research in chemistry and biochemistry, notably that of lipid polymorphism. Organic compounds containing hydrophilic groups at both ends of the molecule are called bolaamphiphilic.
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 . Cell membranes require high levels of cholesterol – typically an average of 20% cholesterol in the whole membrane, increasing locally in raft areas up to ...