M&R Session 1 (Lecture 1.1) Flashcards
What are the general functions of biological membranes?
1) Continuous, highly selective permeability barrier.
2) Control of enclosed chemical environment.
3) Communication
4) Recognition (Signalling molecules, Adhesion proteins, Immune surveillance)
5) Signal generation (electrical and chemical.
What is a membrane composed of (%) ?
Dry Weight:
40% lipid
60% protein
1-10% Carbohydrate
+ 20% total weight is water!
What does the term ‘amphipathic’ mean? Which molecule is present in membranes does this term apply to?
A molecule that has both hydrophobic and hydrophilic regions within it.
Phospholipid.
Describe the structure of a phospholipid.
2 Fatty acid side chains, One Glycerol molecule = Hydrophobic
1 Phosphate and head group (varies) = hydrophilic
What head groups can be present in PLs?
Choline, Amines, Amino Acids, Sugars.
Name 4 PLs found in membranes.
1) Phosphatidylcholine
2) Phosphatidylethanolamine
3) Phosphatidylserine
4) Phosphatidylinositol
What does a C=C do in a FA side chain? In what configuration does this occur?
Introduces a kink into the side chain (reduces PL packing, thus increasing fluidity)
Cis config.
How long can FA side chains be? What are the most common numbers?
C14-24
Usually C16 and C18
How does sphingomyelin differ from ‘classical’ PLs? What about its conformation?
Does not have a glycerol backbone but resembles other PLs in membrane.
Describe a glycolipid.
Sugar containing lipid whereby the phosphocholine moiety is replaced with sugar(s).
How can we classify glycolipids? Name and define the classes.
By the number of sugar molecules attached to the lipid portion.
1) Cerebrosides - head group sugar monomers (e.g. Gal)
2) Gangliosides - head group oligosaccharides
What forms do PLs form when dissolved in water and subjected to sonication?
1) Micelles
2) Bilayers
What is the cholesterol content of the membrane lipid.
45% of total membrane lipid content.
What are the permitted modes of motion for lipid molecules?
1) Intra chain motion - kink formation in the FA chains
2) Fast axial rotation
3) Fast lateral diffusion within the same plane
4) Flip-flop (rare) - movement of lipid molecules from one half of the bilayer to the other (1:1 ratio).
What does cholesterol do to membranes when the temperature is varies?
At low temperatures cholesterol increases the fluidity by interdigitating between PL molecules (reduced PL packing).
At high temperatures it decreases fluidity of the membrane by reducing the PL chain motion (cholesterol is bonded to a PL molecule).
