Biophysical studies of membrane proteins/peptides. Interaction with ...
Biophysical studies of membrane proteins/peptides. Interaction with ...
Biophysical studies of membrane proteins/peptides. Interaction with ...
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sphingomyelin, the most abundant sphingolipid, which is a significant component <strong>of</strong><br />
animal plasma <strong>membrane</strong>s.<br />
1.2.1.3. Glycolipids<br />
Both glycerolipids and sphingolipids can be linked to a carbohydrate in their<br />
headgroups, giving rise to a glycolipid. Glycolipids play important roles in the<br />
interactions <strong>of</strong> the cell <strong>with</strong> its surroundings. Glycoglycerolipids are very abundant in<br />
chloroplast <strong>membrane</strong>s, as well as in blue algae and bacteria. They are however rarely<br />
found in animals (Gennis, 1989). In glycosphingolipids, one or more carbohydrates are<br />
linked to the terminal hydroxyl group <strong>of</strong> the sphingosine backbone. The simplest form<br />
<strong>of</strong> glycosphingolipid is a cerebroside that contains a single carbohydrate residue, either<br />
glucose or galactose. Complex glycosphingolipids called gangliosides present one or<br />
two branched carbohydrate chains containing sialic acid groups. Glycosphingolipids are<br />
as a rule located in the outer surface <strong>of</strong> the plasma <strong>membrane</strong> <strong>with</strong> varying<br />
concentrations (2-10 %), and are particularly abundant in the nervous system.<br />
1.2.1.4. Sterols<br />
The basic structure <strong>of</strong> sterols is a four ring hydrocarbon. This structure confers<br />
the molecule much more rigidity than other lipids. The most important sterol in animal<br />
<strong>membrane</strong>s is cholesterol (Fig. I.3). In cholesterol, a hydrocarbon chain is linked to one<br />
end <strong>of</strong> the ring system and a hydroxyl group is attached to the other end <strong>of</strong> the structure,<br />
this being the polar headgroup <strong>of</strong> the molecule. In the lipid bilayer the molecule is<br />
oriented parallel to the fatty-acid chains <strong>of</strong> other lipids while the hydroxyl group<br />
interacts <strong>with</strong> nearby headgroups. Cholesterol is only found in eukaryotes, particularly<br />
in animal plasma <strong>membrane</strong>s, lysosomes, endosomes and Golgi apparatus. The<br />
concentration <strong>of</strong> cholesterol is especially high in the animal plasma <strong>membrane</strong> (20 - 30<br />
%). In plants cholesterol exists in low amounts, and other sterols are present, namely<br />
sitoesterol and stigmasterol. Ergosterol is found in yeast and other eukaryotic<br />
microorganisms.<br />
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