Structure and function of membranes: Clinical examples and experimental evidence Flashcards
How was flip flop discovered?
Lipid head group modified to carry a ‘spin level’ such as a nitroxide group, whose unpaired electron can be detected by electron spin resonance spectroscopy. The motion and orientation of the lipid in a bilayer can then be deduced from the ESR spectrum. Showed that lipids rarely flip flop, with the exception of cholesterol.
What proves that the cell membrane is a bilayer?
Phosphate heads reacts with dense metals which can easily be seen on the TEM.
If increased microscope magnification, can see two layers
Langmuir trough experiment
Explain Langmuir trough experiment
Lipid molecules arranged in a bilayer, of a known surface area, were added to the water trough and then compressed. The surface area was shown to be twice as much as expected, suggesting that the plasma membrane is composed of two layers.
How was the fluidity of the lipids in the membrane proved?
Frye and Edidin fused human and mouse cells in culture.
Produced monoclonal antibodies specific to the antigens unique to the mouse cell and unique to the human cell.
Tagged the different antibodies with different fluorescent proteins.
Immediately after fusion, the different antibodies were seen to be localised to different parts of the hybrid cell.
After a brief period of incubation, the mouse proteins were intermixed over the cell surface, showing that they moved freely through the plasma membrane
What cells are used to investigate cell membranes + why?
red blood cells, abundant, cells are anucleate so can retain just cell membranes, cells are easy to manipulate
How was aquaporin 1 discovered?
Oocytes were injected with RNA coding for a certain gene. They began to swell under hyoosmotic stress and burst, suggesting that the gene must have coded for water channels
Evidence to show that ATP is needed to pump sodium out in the Na/K pump
Radioactively label sodium-24.
inject inside squid axon
Add metabolic inhibitor- stops pump
Inject ATP directly inside, restores efflux
Therefore efflux of Na+ dependent on ATP supply
How does Multidrug resistance protein transporter work? + example
Uses energy of ATP hydrolysis to extrude hydrophobic compounds from the cell and also functions as a chloride channel. Resistance to chemotherapy in hepatomas.. Chloroquine resistance when treating Plasmodium Falciparum
How does the ABC transporter CFTR work?
Cystic Fibrosis Transmembrane Conductance Regulator- removes CL- from cell, lowers water potential outside, water follows- causes an over accumulation of mucous which is also less viscous.
