Membranes and Receptors Flashcards
Define amphipathic
Contains both hydrophobic and hydrophilic moieties
What are the main kinds of lipids in plasma membranes?
Phospholipids
Glycolipids
Cholesterol
Describe a phospholipid
And the range of head groups it may have
Glycerol backbone
Two fatty acid tails
Phosphate
Polar head groups could be choline, amines, amino acids and sugars
What to cis double bonds do in phospholipids?
They reduce the packing between adjacent phospholipids
Describe plasmalogens and give an example
LOOK OVER AGAIN AND EDIT
Non classical phospholipids such as sphingomyelin
What is the difference between cerebrosides and gangliosides?
Both are glycolipids
Cerebrosides: head group is a sugar monomer
Gangliosides: head group is an oligosaccharide
What are some general functions of membranes?
Barrier: continuous and highly selective Control of enclosed chemical environment Communication: ECF/ICF Recognition: signalling molecules, adhesion, immune surveillance Signal generation in response to stimuli
What is the composition of a membrane?
Percentages dry weight
40% lipid
60% protein
1-10% carbohydrate
Water when hydrated 20% total weight
What sort of movement can lipids do in bilayers?
Intrachain motion: cis formation increases fluidity
Fast axial rotation
Fast lateral diffusion
Flip flop - rare
What are some functions of membrane proteins?
Enzymes Transporters Pumps Ion channels Receptors Energy transducers
Give evidence for proteins in membranes
Functional and biochemical
Functional: facilitated diffusion, ion gradients, specificity of cell responses
Biochemical: membrane fractionation, freeze fracture
What sorts of protein mobility exist in bilayers?
Conformational change
Rotational
Lateral
NO FLIP FLOP: hydrophilic through hydrophobic region not energetically favourable
What restrains protein mobility in a bilayer?
Membrane protein associations make movement sluggish
Proteins prefer cholesterol poor regions, fluid phase
Tethering to the cytoskeleton, other cells, basement membrane, peripheral proteins
What is a peripheral protein?
Associated with the surface
Bound by electrostatic/H bond interactions
Remove with changes in pH or ionic strength
What is an integral protein?
Interacts extensively with hydrophobic regions of the lipid bilayer
Can not remove by changing pH or ionic strength
Can remove with detergents or organic solvents which compete for non polar interactions
Hydrophobic R group residues mainly, alpha helical
1 or many hydrophobic domains
Why is membrane asymmetry important?
Important for function
Receptors for hydrophobic extracellular messenger molecules
Needs to face ECF
Describe how secreted proteins are synthesised
ESA1
Free ribosome
Hydrophobic N terminal sequence
Binds SRP, stops protein synthesis
GTP SRP binds to SRP receptors on the ER
SRP dissociates, protein synthesis continues
Protein into ER pore via PTC
Signal cleaved and the ribosome is recycled
Describe membrane protein biosynthesis
Ribosomes start synthesising, hydrophobic N terminal sequence first
Binds SRP, stops synthesis and binds the SRP receptor, releases SRP
Continues protein synthesis, PTC interacts with signal, further synthesis through the ER
Ribosome is anchored to the pore, hydrophobic a helical area translated
Release of protein and ribosome from PTC, biosynthesis continues in the cytoplasm
What does a hydropathy plot show?
The number of transmembrane domains in an integral membrane protein
How is a membrane protein orientated?
GO OVER WITH MMF NOTES
Positive residues at the C end, N into the lumen
Positive residues at the N end, C into the lumen
Delivered to the membrane by the fusing of vesicles, same orientation as in ER
Shat is the effect of unsaturated fatty acids in a membrane?
Cis double bond
Kink in the chain
Can not pack as tightly
More fluid
Describe the structure of cholesterol
Polar OH head
Rigid steroid ring structure
Non polar hydrocarbon tail
How does cholesterol increase fluidity?
Reduces the packing of phospholipids
Stops crystalline structure at low temperatures
How does cholesterol reduce membrane fluidity?
Reduces chain motion on phospholipids
Rigid sterol structure
Reduces motion at high temps
