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21 Cards in this Set
- Front
- Back
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Describe the Phospholipid Bilayer
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Plasma membrane is a lipid bilayer
Composed of two layers arranged so the nonpolar fatty acid tails face each other while the polar heads face the aqueous solutions Functions as a barrier; polar molecules cannot move in/out of cell without help of proteins Not strength; does not keep the cell together; does not create structure |
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What are the four parts to Phosphotidyl Choline?
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Choline
Phosphate Glycerol Fatty Acid Tails |
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What are four different types of Phospholipids?
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Cholesterol
Phosphatidylcholine Phosphatidylserine Shingomyelin Glycolipids |
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What is the difference between sphingomyelin and the other three types of phospholipids?
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Sphingomyelin is enriched in lipid rafts and does not have a glycerol molecule
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How come the cytosolic side of the membrane is often negatively charged?
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Phosphotidyl serine is negatively charged and is only found in the cytosolic layer
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How come phospholipids in water spontaeously organize into spheres?
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One fatty acid tail has a kink (due to cis double bond) gives phospholipids a cylinder shape
Shape does not allow them to form micelle Polar heads are hydrophilic and the nonpolar tails are hydrophobic Lipids orient themselves so heads contact water and tails don't, sheet folds in on itself to aboid contact with water of fatty acid tails |
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What is the consistency of the lipid bilayer?
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Fluid- lateral diffusion and connot flip-flip
thickness can be altered by number of double bonds and number of carbons |
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What is cholesterol? How does it affect the membrane?
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Cholesterol consists of a polar head group, a rigid steroid ring structure, and a nonpolar hydrocarbon tail
Goes into the center of the lipid bilayer, not comfortable in the presence of water Does not float freely, carried by proteins Impacts fluidity- lessens fluidity, stiffens |
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What is a lipid raft? How come protein composition in a lipid raft is different?
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Enriched with sphingomyelin
Concentrates certain membrane proteins Causes lipid bilayer to be thicker where present |
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What are glycolipids? Where are they found?
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Glycolipids are lipids with sugars attached
The sugars stick out from the extracellular layer of the lipid bylayer and serve as signals Found in the extracellular layer |
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Describe the ways in which a protein can be associated with the membrane
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Membrane proteins can cross as: alpha helix, beta barrel, attached to a lipid, attached to a glycolipid, attached to other membrane proteins, can be structural
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How do most transmembrane proteins cross the lipid bilayer?
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As an alpha helix
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What is a hydropathy plot? Spanning regions?
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Hydropathy plots are used to find clusters of hydrophobic amino acids which could indicate that the polypeptide in question is a transmembrane protein
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How are membrane proteins solubilized?
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Detergents are added to separate the protein from the lipid bilayer
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What is a red blood cell ghost?
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A ruptured cell membrane of a red blood cell. The insides spill out and all that's left is the membrane and membrane proteins.
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What is the function of most membrane proteins in the red blood cell?
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Structural
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What is the function of band three?
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Transports HCO3 across the red blood cell membrane
Functions as anion (neg. charge) transport |
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What is freeze fracture electron microscopy?
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Freeze cell rapidly
No ice in lipid bilayer= weakest point Take a razor to block of ice- split=proteins go with outside or inside of lipid bilayer determined by where the majority of the protein is located |
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How come glycophorin and band three end up in different fractions during freeze fracture electron microscopy?
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Most of band three is in the cytosol
Most glycophorin is located in the extracellular layer |
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How do we know proteins diffuse in the membrane? What is FRAP?
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FRAP= Fluorescent Recovery After Photobleaching
Can measure protein movement in membrane Make a protein fluorescent with green flourescent protein (GFP) Rate of recovery determines how fast proteins are diffusing in the membrane |
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How can the lateral mobility of membrane proteins be constrained?
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Attach to large protein complex
Attach to extracellular molecules Attach to proteins inside cell Attach to other cell's proteins |
