I sem and II yr Botany Hons SKBU

4. Membrane structure best
demonstrated by fluid mosaic
model and t membranes
consist of:
phospholipids arranged in a
bilayer
globular proteins inserted in
the lipid bilayer

5. Phospholipid structure consists of
•glycerol – a 3-carbon polyalcohol acting as a backbone for the phospholipids
•2 fatty acids attached to the glycerol Their nonpolar nature makes them hydrophobic
(“water-fearing”).
•Posphate group attached to the glycerol (The phosphate group is polar and hydrophilic
(“water-loving”).
The partially hydrophilic,
partially hydrophobic
phospholipid
spontaneously forms a
bilayer:
-fatty acids are on the inside
-phosphate groups are on
both surfaces of the bilayer

8. (1) a single a helix,
(2) as multiple a helices, or
(3) as a rolled-up b sheet (a barrel). Some of these "single-pass" and "multipass" proteins
have a covalently attached fatty acid chain inserted in the cytosolic lipid monolayer. Other
membrane proteins are exposed at only one side of the membrane.
(4) Some of these are anchored to the cytosolic surface by an amphipathic a helix that
partitions into the cytosolic monolayer of the lipid bilayer through the hydrophobic face of
the helix.
(5) Others are attached to the bilayer solely by a covalently attached lipid chain either a
fatty acid chain or a prenyl group in the cytosolic monolayer or,
(6) via an oligosaccharide linker, to phosphatidylinositol in the non cytosolic monolayer.
(7, 8) Finally, many proteins are attached to the membrane only by non-covalent
interactions with other membrane proteins.

10. Membrane Sugar
•Sugar moieties of glycolipid protruding outward in plasma membrane.
•No sugar on inside

11. Permeability coefficient of membrane
Water, urea, glycerol, indole, tryptophan, glucose, O2,CO2 & N can easily pass
Na, K Cl lag behind