Biochemistry Lecture No.11: Biological Membranes
Friday September 28 , 2012
-Amphipathic lipids have polar groups on one part of the molecule and non-polar ones on the other part
and have opposite natures. This results in hydrophilic heads and hydrophobic tails. It is not favourable
for the hydrophobic tails to be exposed to water, so they will cluster together to avoid contact
The Lipid Bi-Layer:
-The lipid bi-layer consists of two sheaths or rows of phospholipids with their hydrophobic tails facing
each other. The hydrophobic groups are completely shielded by the hydrophilic phosphates. This
structural design forms the physical basis of the cell membrane.
Diffusion Of Lipids Within The Bi-Layer:
-Lipids move about plane of the lipid bi-layer. Rate that lipids diffuse is a result of the fluidity of the
membrane, which is determined by four key factors: temperature (warmer = faster diffusion; colder =
gel-like lipid bi-layer), length of chains (longer chains = more Van der Waal’s force and less diffusion;
shorter chains more fluid), degree of unsaturation (more double bonds = more fluid due to kinks; less
double bonds = less diffusion), and the cholesterol concentration.
Cholesterol & Membrane Fluidity: