CELL MEMBRANE
IT is the outer envelope of the cells which is thin and elastic it is only 5 to 10 nanometer thick and composed almost entirely of proteins and lipids and small amount of corbohydrates the approximate chemical composition is protein55 lipids42( phospholipids 25 cholesteral 13 other lipids 4 ) and carbohydrates 3
basic structure of cell membrane
the cell membrane consists of lipid bilayer which is a thin film of lipids only two molecules thick that is continuous over the entire cell surface interspersed in this lipid film are large globular protein molecules
the lipid bilayer is mainly composed of phospholipid molecules the end which contains phosphate group is polar and therefore soluble in water the other end of the phospholipid molecule is highly non polar the polar portion project to outer sides of the membrane whereas the non polar (hydrophobic) portion of phospholipid remains in the centre
the lipid layer because of hydrophobicity repels water soluble substances such as electrolytes glucose urea etc and thus prevent their entry into the cell fat soluble substances such as oxygen carbondioxide and alcohol can easily penetrate the lipid membrane
The cell membrane is not solid in nature but it is fluid therefore portions of the membrane can literally flow from one point to another along the surface of the membrane proteins from one area can migrate to the other area
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