Session 1.2: Membrane Bilayer Flashcards
What are the functions of biological membranes
Regulate movement as highly selective permeability barrier
Control of the enclosed chemical environment - not susceptible to outside
Communication
Recognition - signalling molecules, adhesion proteins and immune surveillance (antigens)
Signal generation in response to stimuli (electrical, chemical)
Are all membranes the same
?
Which lipids are involved in biological membranes?
Phospholipids
Glycoplipids
Cholesterol
What is meant by a fluid membrane
Dynamic environment in which lipds move around is have mobile environment, proteins embedded will also move
How does cholesterol contribute to membrane stability? Does it increase or decrease fluidity?
Increasing temperature - rate of energy heat flow
At a given temperature, energy input causing melting of the phospholipid bilayer
As add cholesterol, more fluid. Stabilising the membrane properties over a temperature range
Both:
Hydroxyl group of the cholesterol forms a hydrogen bond with the carbonyl oxygen of the carboxylic group of the fatty acid. Locking cholesterol into an adjacent phospholipid. As the fatty acid was moving, now stops, reducing motion and fluidity
Also causes reduces phospholipid packing increasing fluidity
Prevents the phospholipid membrane from becoming too fluid and not enough fluid
What type of movement occurs across phospholipids
Lateral diffusion
Up to 2um per second
How do lipids move
Brownian motion - random vibration
How do phospholipids move
Dynamic due to flexion of the tails which bounce against other tails, and rotation of the lipid
Flip flop - hydrophilic heads and hydrophobic tails flip sides
Vibration
Lateral motion
What is the structure of a phospholipid molecule
2 fatty acids - CIS double bond then unsaturated reduce phospholipid packing and more movement as introduces kink. Or saturated - less movement, rigid. The chains can be between 14 and 24 C’s long. C16 and C18 is most prevalent
Glycerol
Phosphate
Head groups - choline, amino acids, amines, sugars (small)
How are unsaturated fatty acids formed
After C-9 can’t be formed, must be given in food
What is the structure of cholesterol
Polar head group
Rigid planar steroid ring - haxgonal and pentagonal
Non polar, hydrocarbon tail
A solid structure with a flexible tail
What are lipid rafts
Dynamic
Made of cholesterol
Comprised of sphingolipids with saturated fatty acids and tightly intercalated cholesterol
Patches of membrane with reduced fluidity
Most proteins prefer to be in fluid - but can exclude or include membrane proteins (lipid rafts - dint like)
Raft affinity for proteins modulated by intra or extraceullar stimuli
Proteins can move in or out
Receptors found on rafts
What are the functions of lipid rafts
Important for Scaffolding proteins - which is then involved in Signal transduction from outside cell to inside cell
Includes GPI anchored proteins, double acylated (fatty acid modifications on them), alpha subunit of heterotrimetric G proteins
Crosslinking for signalling molecules increases their affinity for rafts
Partitioning changed their micro-environment, making new interactions possible, enhancing their signalling
Overall - raft clustering amplifies signalling by bringing signalling components together
What is the structure of a membrane bilayer
?
What other regions of plasma membrane funcions are there?
Interaction with basement membrane Interaction with adjacent cells Absorption of bodily fluids Secretion Transport Synapses - nerve junctions Electrical signal conduction - axial Changing shape may change the properties of a particular region
By weight, what is the most abundant part of the membrane bilayers?
40% lipid
60% protein
1-10% carbohydrate
20% water
Membrane lipids are amphipathic molecules, what do Ed that mean
Contain both a hydrophilic and a hydrophobic parts
What other lipids are in the membrane
Sphingonyelin which a sphingolipid backbone
If you replace the phospholipid part with a sugar = glycolipid
What is the structure of a glycolipid
2 fatty acid chains
Sphingolipid backbone
Single monosaccharide head group - cerebroside
Oligosacharide head group - ganglioside (in nervous system and diseases use to gain entry)
What are the similarities of membrane lipids
Small head group
Fatty acyl chains of similar length
What is a lipid micelle
In water
Hydrophilic head groups on outside
Hydrophobic tails in inside
Spherical shape formed
What is a lipid bilayer
In aqueous conditions
Hydrophilic head groups outward
Hydrophilic inside
Ordered sheet of membrane. Sea of lipid stabilised by interactions with water
What stabilised the membrane structure
Hydrogen bond with aqueous environment
What are functions of liposomes
Delivery of drugs to target tissue
