What are the functions of biological membranes?
1. Selective permeability barrier
2. Comparmentalization of functions.
5. Energy storage
What are common features of biological membranes?
1. Sheetlike structures that can form closed boundaries in aqueous solution
2. Composed of lipid, protein, and carbohydrate
3. Lipid bilayer is relatively impermable to polar molecules
4. Membrane proteins carry out most specific fxns
5. Membranes are held together by non-covalent interactions
6. Biological membranes are asymmetric
7. Membranes are fluid under physiological conditions
Membrane lipids are .....
AMPHIPATHIC! - both hydrophobic (hydrocarbon tails) and hydrophilic (polar head groups)
Describe the structure of a phospholipid
Describe the effect of saturation and length of fatty acids chains
Increased saturation and increased length leads to decreased fluidity
What confirmation are naturally occuring unsaturated fatty acid chains in?
Describe the general structure of phospholipid backbone and give examples.
Glycerol or sphingosine (in sphingomyelin) - attach to fatty acids and phosphate via hydroxl groups
Glyercol attaches to 2 fatty chains, sphingosine carries on hydrocarbon of its own
What composes a phospholipid headgroups and give some examples
Phosphate + alcohol, ex. serine, choline, inositol, ethanolamine, etc.
What are other components of the membrane?
Glycolipids - sphingosine backbone w/ sugar attached
Cholesterol - makes membrane less flexible
Memorize the amphipathic properties of membrane lipids...
What are the forces at play in the spontaneous formation of lipid bilayers?
Hydrophobic effect, van der Waals, electrostatic and H bonding
What is the difference between transverse and lateral diffusion of membrane lipids
Transverse (flip flop) - very slow, protein mediated
Lateral - all the fucking time, gives fluidity
What are factors affecting fluidity?
1. Temp - needs to be above "melting temperature" to be fluid and free flowing
2. Length and degree of unsaturation of fatty acid chain - shorter, unsaturated = ^^ fluidity
3. Cholesterol content - decreases fluidity (lipid rafts)
What factors make a substance imperable to a lipid bilayer?
1. Polarity - ^ polarity means it won't get through
2. Size - the larger the molecule, the more difficult it will be to get through
How do drugs get into cells?
1. Passive diffusion
2. Hijacked transporters
3. Liposome delivery
4. Protein transduction
What is the relative ratio of lipid to proteins in the membrane?
Differs but around 1:1, there's more protein than people think
Types of membrane proteins...
Integral membrane proteins - transmembrane, monolayer associated, lipid linked - amphipathic to be inserted into membrane
Peripheral membrane proteins - protein attached
Fluid mosaic model
1. Lipid bilayer acts as solvent for membrane proteins
2. Membrane proteins are free to diffuse laterally, but cannot flip-flop
How can lateral diffusion of membrane proteins be constrained?
1. Anchoring protein to intracellular structure
2. Anchoring protein to extracellular structure
3. Protein/protein interactions b/n cells
4. Barriers by junction proteins
Describe lipid rafts
Regions of membrane that are more rigid and resistant to solubilization
Specific proteins are recruited for...
1. Signal transduction
2. Protein sorting
4. Viral entry/exit
Describe some special properties of lipids in a membrane
Abnormal lipid distribution signal cells are dying