Session 1 Flashcards
What is an amphipathic molecule?
One that contains hydrophobic and hydrophillic sections
What is the cell membrane mostly made of?
Protein then lipids
What are the main types of lipids in the membrane?
Phospholipids
What is special about the phospholipid fatty chain?
It is unsaturated and in the cis form. This causes a kink in the chain so reduces phospholipid packing.
What are the types of phospholipids?
Plasmalogens,
Spingomyelin
Glycoproteins
What are the 2 types of Glycerol molecules?
Extra point - What is different about them?
Cerebrosides and Gangliosides
Extra point - Cerebrosides have head group sugar monomers. Gangliosides have head group sugars oligosaccharides.
How much of the membrane lipids does Cholesterol make?
45%
What are the 2 shapes amphiphatic molecules can form in water?
Miscelles and Bilayers
What causes bilayer formation of phospholipids in water?
Van der Waals forces between the hydrophobic tails
What stabilises the co operative shapes of phopsholipids in water?
The electrostatic and hydrogen bonds between the hydrophobic sections and interactions between hydrophillic groups and water.
What are the ways a lipid molecule can move within a bilayer?
Intra chain motion
Fast axial rotation
Fast lateral diffusion (within the plane of the bilayer)
Flip Flop (From one half of the bilayer to the other on a one for one exchange basis)
What is the functional evidence for membrane proteins?
Facilitated diffusion
Ion gradients
Specificity of cell responses
What is the Biochemical evidence for membrane proteins?
Fractionation and gel electrophoresis of the membrane.
Freeze fracture.
What is Freeze Fracture?
A technique where a frozen cell is broken at its weakest section (Usually plasma membrane) then the ice is removed and a slide is placed under the electron microscope.
What are the ways a membrane protein can move?
Extra point - Why can’t they flip flop?
Conformational change
Rotation
Lateral
Extra point - They have large hydrophilic sections so too much energy is required for them to move through the hydrophobic section of the bilayer.
What are the restrictions on protein’s mobility in a bilayer?
Lipid mediated effects. (Tethering)
Membrane proteins associations (Aggregations)
Association with extra membranous proteins (interaction with other cells)
How are peripheral membrane proteins bound to the surface of membranes?
Extra point - How can they be removed?
By electrostatic and hydrogen bonds.
Extra point - By changes in pH or ionic strength.
How are integral membrane proteins bound to the membrane?
Extra point - How can they be removed?
They interact with the hydrophobic region of the bilayer (So cannot be removed with pH or ionic manipulation)
Extra point - Can be removed using agents that compete for the non polar interactions (eg detergents)
What is the difference between membrane protein synthesis and secretory protein synthesis?
Extra point - How does it achieve this?
Membrane proteins need to span the membrane of a vesicle instead of being contained in it.
Extra point - The addition of a stop transfer signal.
What can a hydropathy plot be used for?
Can be used to see how many transmembrane regions a protein has.
Why is membrane asymmetry important?
For function. eg a receptor needs to have its recognition site towards the extracellular space.
What property of unsaturated fatty acid chains causes an increase in membrane fluidity?
The double bonds allow cis formation to cause a kink in the chain which reduces packing.
How does Cholesterol help stabilise the plasma membrane?
Extra point - What does this remove?
Hydrogen bonding to the fatty acid chains.
Extra point - The endothermic phase transition (Where the molecules melt into a liquid.)
Cholesterol increases membrane fluidity and decreases it at the same time. Why?
Cholesterol reduces the phospholipid packing (Increasing fluidity)
Cholesterol reduces phospholipid chain motion (decreases fluidity)
What effects lateral diffusion of proteins through the membrane?
Size - Protein aggregation and interacgtion with other extracellular proteins/cytoskeleton.
Lipid mediated effects - proteins separate into fluid phase or cholesterol poor regions.
What is the cytoskeleton made of?
Spectrin and Actin molecules attached to the membrane by adapter proteins (Ankyrin and Glycophorin)
What does attachment of an integral membrane protein to the cytoskeleton restrict?
Lateral mobility of the membrane protein.
Why is the erythrocyte skeleton so important?
Because without it the RBCs lose their shape and are lysed by shearing forces then cleared by the spleen.
In what diseases is the erythrocyte skeleton destroyed?
Haemolytic anaemias.
What is depleted in hereditary spherocytosis?
Spectrin levels (In common dominant form)
How does hereditary spherocytosis lead to haemolytic anaemia?
Increases lysis of RBCs so they have a shorter lifespan. The bine marrow cannot compensate and haemolytic anaemia develops.
What is the pathophysiology of hereditary elliptocytosis?
The spectrin molecules cannot form heterotetramers, results in fragile elliptoid cell shapes instead of biconcave which then lead to haemolytic anaemia.
