Flashcards in MR 1 Deck (18)
Which is the only phospholipid not based on glycerol?
Phospholipids have a double bond - what does this introduce into the chain?
A kink. This increases fluidity by decreasing packing.
What two structures do lipids form in water?
Micelles or bilayers.
Name the way lipids are can move around in the bilayer.
Fast axial rotation
Lateral diffusion within the plane of the bilayer.
Intra chain motion
What methods give us evidence for proteins?
Describe the mobility of proteins
Conformational change - eg open/close
Explain why proteins cannot flip flop
They have too much of a hydrophilic structure that would need the pass through the lipid layer - requires too much energy. Also, a change in proteins in the bilayer would be too disruptive.
Distinguish between peripheral and integral proteins.
- not embedded
- can be removed via changes in the ionic and pH strength
- bound to the membrane via electrostatic forces
- can't be removed via pH/ionic changes.
- needs a detergent that can compete for the non polar interactions
- they interact with the hydrophobic regions of the bilayer extensively
Describe in general terms the mechanism of membrane insertion of integral proteins
- protein synthesis occurs on ribosome. A hydrophobic N-terminal signal sequence is produced, which is recognised by Signal Recognition Particle (SRPs). SRP binds, along with GTP.
- binding of GTP-SRP stops protein synthesis and directs the ribosome to the ER. As it binds, the SRP dissociates.
- protein synthesis resumes into the lumen of the ER, via pores which are known as protein translocating complex.
- At a certain point, a highly hydrophobic sequence is encountered by the ribosome
-this sequence is 18-20 AA long which spans the membrane. It effectively locks the protein into the membrane.
- the remainder of the protein is synthesised in the cytosol.
- this way, the part before the hydrophobic sequence is inside the membrane. The other side of the sequence is outside
- hence it spans the membrane.
Discuss membrane asymmetrically
Asymmetrical orientation is important for function.
Eg the receptors for hydrophilic extracellular molecules must have their recognition site directed to the surface.
Describe the influence of FAs on membrane fluidity.
Increase membrane fluidity due to the kink that is introduced into the chain, which reduces packing.
Decreases packing by reduced chain motion of phospholipids.
Describe the influence of cholesterol on membrane fluidity.
Increases fluidity by reducing packing.
Decreases fluidity by decreasing phospholipid chain motion
Stabilises membrane by hydrogen bonding to fatty acids. (This abolishes the endothermic phase transition).
Why is the membrane bilayer often referred to as a 'fluid mosaic model'
Fluid - as the phospholipids are mobile hence fluid m
Mosaic - the bilayer constitutes many different components like a mosaic
Name some constituents of the membrane bilayer
What does the membrane cytoskeleton consist of?
(Hint: think of RBCs)
Make references of these to integral proteins.
Composed of spectrin and actin - these are peripheral proteins.
Ionic wash of RBCs sees these form a cytoskeleton which is facing the cytosol.
Spectrin attached to Ankyrin and then to Band 3 (integral protein)
Actin attached to Glycophorin and then to Band 4.1 (integral protein)
Integral proteins are attached to cytoskeleton via Ankyrin and Glycophorin. What does this attachment mean for their movement ?
Reduces their lateral movement within the bilayer.
Describe what Hereditary spherocytosis is, and how it leads to haemolytic anaemia.
H.S is the reduction of spectrin (which is connects to Band 3 via Ankyrin, forming part of the cytoskeleton) by around 40-50%.
- this reduces the lifespan of the RBC
- RBC tend to 'round up' and are lysed by the sheering forces in capillaries.
- increase RBC lysis by spleen - bone marrow cannot compensate
- there is a deficit of RBC
- hence, haemolytic anaemia.