Session 1 Flashcards
What percentage of the membrane is protein and what percentage is lipid?
60% protein
40% lipid
Traces of carbs
What are the general functions of biological molecules?
Highly selective permeable barrier, control of enclosed chemical environment, communication, recognition, signal generation in response to stimuli
What is an amphipathic molecule?
Molecules which contain both hydrophobic and hydrophilic regions (moieties)
What are the predominant lipids in the membrane?
Phospholipids e.g. phosphatidylcholine
What are the different types of head groups?
Cholines, amines, amino acids and sugars
What variety of fatty acid chains are the most prevalent?
C16 & C18
Unsaturated fatty acid side chains in cis formation introduce a kink in the chain which reduces phospholipid packing
Describe plasmalogens
Only phospholipid not based on glycerol e.g. sphingomyelin
Describe glycolipids
Sugar containing lipids. Cerebrosides - head group sugar monomers. Gangliosides - head group oligosaccharides
Describe choesterol
A plasma membrane lipid which accounts for 45% of the total membrane lipid.
How are bilayers formed?
By congregation of amphipathic molecules. Occurs spontaneously due to van der Waals forces between hydrophobic tails. Co-operative structure is stabilised by non-covalent forces; electrostatic and H-bonding between hydrophilic moieties and interactions between hydrophilic groups and water
What are the four permitted modes of mobility of lipids in a lipid bilayer?
Intra-chain motion (kink formation in the fatty acyl chains)
Fast axial rotation
Fast lateral rotation
Flip-flop (movement of lipid molecules from one half of the bilayer to the other on a one for one exchange basis)
How does cholesterol affect the lipid bilayer?
Prevents crystalline formation of phospholipids which increases fluidity and prevents leakage of ions. It also decreases phospholipid chain movement which decreases fluidity.
What are the functions of the plasma membrane?
Interaction with the basement membrane, interaction with adjacent cells, absorption of body fluids, secretion, transport, synapses nerve junctions, electrical signal conduction and changing shape
What are the functions of membrane proteins?
Enzymes, transporters, pumps, ion channels, receptors and energy transducers.
What modes of motion are permitted for proteins?
Conformational changes, rotational and lateral