The Membrane Bilayer: Main Biophysical Properties Flashcards
What are the functions of biological membranes?
Continuous highly selective permeability barrier
Control of the enclosed chemical environment
Communication
Recognition - signalling molecules
Adhesion proteins and immune surveillance
Signal generation in response to stimuli which can be chemical and electrical
Secretion and absorption
What is the plasma membrane composed of?
By dry weight:
40% lipid
60% protein
1-10% carbohydrates which have been added by glycosylation to lipids and proteins
If you do not count dry weight around 20% is water.
The membrane lipids are amphipathic molecules. What does this mean?
They contain both hydrophilic and hydrophobic chemical groups.
Outline the structure of the phospholipid.
Two fatty acids attached to a glycerol molecule. The glycerol molecule is then attached to a phosphate group and the phosphate group is attached to a head group.
What special properties do the tails vs the heads have?
The heads are hydrophilic, the tails are hydrophobic. One of the tails also have a kink in it.
Give some features of the head groups.
Range of polar head groups which are hydrophilic
Examples like choline, amino acids and sugars.
Give some features of the fatty acid chains.
Length between C14 and C24.
C16 and C18 is most common.
Cis double bond introduces a kink
Hydrophobic.
What different phospholipids are there?
Phosphoglycerides and Sphingomyelin
There is another lipid that is present in the lipid bilayer. Which?
Glycolipids with the sub groups cerebrosides and gangliosides.
What different movements can the phospholipids have?
Flexion
Rotation
Lateral diffusion
Flip flop
Why are the cis double bonds that introduce the kinks in the lipid bilayer important?
The kinks reduces the phospholipid packing. This means that it is not as packed with the cis double bonds and produces a more dynamic and fluid environment.
Give some features of cholesterol.
A polar head group.
A rigid planar steroid ring structure
A non-polar hydrocarbon tail.
Why is cholesterol important in the lipid bilayer?
It stabilises the lipid bilayer.
It can either make the lipid bilayer more rigid or more fluid. It reduces phospholipid chain motion which makes it more rigid, however it also reduces phospholipid packing which increases the fluidity.
