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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 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 ...
The hydrophobic core of the phospholipid bilayer is constantly in motion because of rotations around the bonds of lipid tails. [13] Hydrophobic tails of a bilayer bend and lock together. However, because of hydrogen bonding with water, the hydrophilic head groups exhibit less movement as their rotation and mobility are constrained. [13]
In organisms, the cell membrane consists of a phospholipid bilayer. In the bilayer, the phospholipid molecule is movable. These movements are categorized into two types, lateral movements and transverse movements (also called Flip-Flop). The first is the lateral movement, where the phospholipid moves horizontally on the same side of the 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).
Phospholipids and glycolipids consist of two long, nonpolar (hydrophobic) hydrocarbon chains linked to a hydrophilic head group. The heads of phospholipids are phosphorylated and they consist of either: Glycerol (and hence the name phosphoglycerides given to this group of lipids), or; Sphingosine (e.g. sphingomyelin and ceramide).
Although it is a lipid, cholesterol bears little resemblance to a phospholipid. The hydrophilic domain of cholesterol is quite small, consisting of a single hydroxyl group. Adjacent to this hydroxyl group is a rigid planar structure composed of several fused rings. At the opposite end of the ring structure is a short single chain tail.
In the fusion process, the lipid head group is not only involved in charge density, but can affect dehydration and defect nucleation. These effects are independent of the effects of ions. The presence of the uncharged headgroup phosphatidylethanolamine (PE) increases fusion when incorporated into a phosphatidylcholine bilayer.