The Phospolipid Bilayer

Our cell membrane is made up of a dispersion of different proteins onto a 2 dimensional fluid of lipids, compounded mainly of phospholipids, a class of membrane lipids that are amphipathic in their properties, meaning that they are both hydrophilic and hydrophobic (Ratto, 2002).Of all the phospholipids, the most common type that makes up most cell membranes is phosphatidylcholine, which has a hydrophilic head group and two hydrophobic hydrocarbon tails (Alberts et al, 1998, p349).Because of their hydrophobic nature, the hydrocarbon tails resist against the aqueous environment, thus, forcing away from it leaving the hydrophilic head groups exposed to the aqueous environment, hence, forming a bilayer (Alberts et al, 1998, p350).The hydrophilic head groups face the outside environment and the hydrophobic tails face each other (Hanke and Schlue, 1993).The main focus is, however, the fluidity of the phospholipid bilayer and a disease involving the phospholipid bilayer called Antiphospholipid Syndrome.
The phospholipids in membranes are fluid because they can move laterally from one place to another in the plane of the bilayer without being restrained (Alberts et al, 1998, p352); hence, scientists named the phospholipid bilayer "The Fluid Mosaic Model" (Hanke and Schlue 1993). The only movement that they cannot do is flip-flop from one leaflet of the membrane to another; therefore, in order for the phospholipids to be transferred from one leaflet to another, the enzyme flipase is required to catalyze this transfer (Alberts et al, 1998, p352).One experiment that scientists manipulated to prove this was the Fluorescent Recovery After Photo-Bleaching (FRAP) experiment (Bultmann, T. et al, 1991).On a region of the cell surface, scientists labeled it by fluoresce and by doing this, the fluorochrome of the dye will covalently attach to the lipid or protein molecules.When this region is illumina

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