are similar to cell membrane which occur within the cytoplasm. The endomembrane system is evolved from the inward growth of cell membrane in the ancestors of the first eukaryotes (Figure . ). .
. Endoplasmic Reticulum The largest of the internal membranes is called the endoplasmic reticulum (ER). The name endoplasmic reticulum was given by K.R. Porter ( ).
It consists of double membrane. Morphologically the structure of endoplasmic reticulum consists of the following: Fluid Mosaic Model Jonathan Singer and Garth Nicolson ( ) proposed fluid mosaic model. It is made up of lipids and proteins together with a little amount of carbohydrate. The lipid membrane is made up of phospholipid.
The phospholipid molecule has a hydrophobic tail and hydrophilic head. The hydrophobic tail repels water and hydrophilic head attracts water. The proteins of the membrane are globular proteins which are found intermingled between the lipid bilayer most of which are projecting beyond the lipid bilayer. These proteins are called as integral proteins .
Few are superficially attached on either surface of the lipid bilayer which are called as peripheral proteins . The proteins are involved in transport of molecules across the membranes and also act as enzymes, receptors (or) antigens. Water-loving polar molecule are called hydrophilic molecule. They have polar phosphate group responsible for attracting water.
Water hating non-polar molecule are called as hydrophobic molecule. They have fatty acid which is non-polar which cannot attract water Carbohydrate molecules of cell membrane are short chain polysaccharides. These are either bound with ‘ glycoproteins ’ or ‘ glycolipids ’ and form a ‘ glyocalyx’ (Figure . ).
The movement of membrane lipids from one side of the membrane to the other side by vertical movement is called flip flopping or flip flop movement . This movement takes place more slowly than lateral diffusion of lipid molecule. The Phospholipids can have flip flop movement because they have smaller polar regions, whereas the proteins cannot flip flop because the polar region is extensive. dictyosomes .
Golgi apparatus is a stack of flat membrane enclosed sacs. It consist of cisternae, tubules, vesicles and