Membrane Cytoskeleton Interactions and Asymmetry

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  • Created by: LucyLaa
  • Created on: 13-10-18 20:30
Why are cells asymmetric?
Proteins have different functions e.g. channels, receptors, enzymes, carriers, cell-cell recognition, cytoskeleton, intracellular transport etc.
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What is an erythrocyte?
Red Blood cell
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What is an RBC ghost?
A clean preparation of plasma membrane when haemoglobin washed away
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Why is an RBC biconcave?
Increases SA to carry haemoglobin
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How are RBC ghosts used?
Run on SDS page gels, agarose gel under electric field and use western blot, take gel and stain separated proteins, see simple protein composition
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What does spectrin form?
Dimers
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What can mutations in spectrin cause?
Fragility --> patients can have haemolytic anemia
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Name 3 peripheral proteins in the cytoskeleton of RBCs
Spectrin, Actin (in a complex with tropomyosin, band 4.1 and adducin), and Ankryin
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Name 2 transmembrane proteins
Glycophorin and Band 3
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Which moves more rapidly: proteins or phospholipids?
Phospholipids (less constrained than proteins)
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How are proteins constrained?
Can be: tethered to cytoskeleton; mesh-work close to membrane acts as a diffusion barrier; tight junctions prevent free movement of proteins into different domains
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In which leaflet is the segregation of lipids?
Outer leaflet --> tight junctions localise the lipids
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How is lipid movement restricted?
Binding to particular proteins; segregated into domains (e.g. lipid rafts); physical barriers (e.g. tight junctions)
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What is the glycocalyx?
Sugary layer on the outside of cells formed by glycolipids and glycoproteins
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What is the function of the glycocalyx?
Protection, quick responses in signalling e.g. Blood Group System
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Which blood group is the universal donor?
O
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Which blood group is the universal acceptor?
AB
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Why might the phospholipid bilayer be asymmetric?
Inner surface may be negatively charged to maintain electrochemical gradient, or certain proteins may be needed in signalling cascades
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What is the enzyme that equilibrates lipids when more phospholipids are added to one side of the bilayer?
Scramblase
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What does this enzyme do within the membrane?
It flips the phospholipid molecules so they are symmetrical
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What is the enzyme that catalyses the flipping of specific phospholipids to cytoplasmic monolayer using ATP?
Flippase
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What does aminophospholipid translocase do to the membrane?
It transports phosphatidylserine and phosphatidylethanolamine from one side of a bilayer to another
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Why is phospholipid asymmetry important?
Coagulation (translocase activity inhibited so phosphatidylserine ends up in outer leaflet and provides nucleation site for cascade); Scott's Disease (deficiency of scramblase so no clotting); cell recognition and apoptosis
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Card 2

Front

What is an erythrocyte?

Back

Red Blood cell

Card 3

Front

What is an RBC ghost?

Back

Preview of the front of card 3

Card 4

Front

Why is an RBC biconcave?

Back

Preview of the front of card 4

Card 5

Front

How are RBC ghosts used?

Back

Preview of the front of card 5
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