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Cell Membrane

Thickness 7-10 nm. The fluid mosaic model of membrane structure proposed in 1972 by Singer and Nicolson. Contain lipids (bilayer), proteins & carbohydrates.


A.  Lipids:
30-40% of cell membrane consists of three classes of amphipathic lipids: phospholipids,  glycolipids, and steroids. The phospholipids are the most abundant. In animal cells cholesterol is normally found dispersed in varying degrees throughout cell membranes, in the irregular spaces between the hydrophobic tails of the membrane lipids, where it confers a stiffening and strengthening effect on the membrane. lecithin is phosphatidylcholine
 a type of phospholipid which is a integral part of cell membrane. Cell membrane contains triglycerides close to zero.


B. Carbohydrates:
Plasma membranes also contain carbohydrates, predominantly glycoproteins, but with some glycolipids (cerebrosides and gangliosides). For the most part, no glycosylation occurs on membranes within the cell; rather generally glycosylation occurs on the extracellular surface of the plasma membrane. The glycocalyx is an important feature in all cells, especially epithelia with microvilli. The penultimate sugar is galactose and the terminal sugar is sialic acid. Sialic acid carries a negative chargeQ, providing an external barrier to –vely charged particles.


C.  Proteins: 50-60% of cell membrane. 3 types]




1.    Integral proteins or transmembrane proteins

:Ion channels,

2.  Lipid anchored proteins:

:G proteins

3.  Peripheral proteins:            

:Some enzymes & hormones

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