Signal Transduction - Membranes

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Signal Transduction - Membranes
2013-02-01 17:49:21
Biology James Jim Thomas Signal Transduction Biochemistry

Signal Transduction
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  1. What is the definition of Amphiphillic.
    A molecule with both Hydrophillic and Hydrophobic properties.
  2. What is a Phosphoglyceride?
    • A similar molecule to a triglyceride, whereby on of the hydroxyl groups is attached to a phosphate-based group.
  3. What is a "Leaflet"?
    A leaflet is one side of a monolayer.
  4. Breifly describe "spin labeling" in terms of membranes.
    • Spin labeling is the process by which an atom in a species (often nitroxyl) can be traced by interacting with unpaired electrons in a similar way to NMR.
    • Spin labeling is often used to trace the motion of phospholipids within a membrane.
  5. Can phospholipids migrate between leaflets? If so, how often does this occur?
    Phospholipids can migrate in a process known as "flip-flop", however they only do so rarely.
  6. What is another Term for Cytosolic?
  7. How might a newly created Phosphoglyceride get to the extracellular leaflet?
    It could "flip-flop" randomly (very rare), or it could do so with the aid of phospholipid translocators.
  8. What is the phase transition of a membrane?
    The temperature at which it's phospholipids make up a crystalline structure.
  9. What might affect Phase Transition?
    • Chain length (More, stronger interactions).
    • Saturation (Unsaturated chains pack less efficiently, therefore interact less).
  10. With respect to membrane fluidity, what might a Yeast cell do in response to a temperature drop?
    A yeast cell will make it's phospholipid tails shorter in response a drop in temperature in an attempt to moderate fluidity.
  11. How does Cholesterol affect membranes?
    Cholesterol's rings immobilize the upper end of fatty chains of local phospholipids. Therefore the membrane becomes more rigid and less permeable to water soluble particles.
  12. Does Cholesterol affect Permeability, Solubility, or Both.
    Cholesterol mostly affects permeability. However is also affects the fluidity of the membrane in high concentrations such that it prevents crystallization.
  13. Could this picture be an accurate example of a membrane? Explain.
    Yes. It could be an example of a Lipid Raft. Often, Lipids with longer tails will come together to accommodate specific proteins.
  14. What is the Indicator "A" referring to in the following picture? Why is it between two monolayers?
    • A Lipid Droplet.
    • It is between two monolayers because it is hydrophobic and therefore will interact with the hydrophobic ends of the phospholipid tails.
  15. What are Lipid Droplets?
    Reservoirs in the membrane containing neutral, hydrophobic, lipids.
  16. Are the Intracellular and Extracellular sides of a membrane the same? If not, how so?
    • No, the cell membrane is asymmetric.
    • The membrane can differ in concentrations of phospholipids, charge, proteinds, carbohydrates and more.
  17. Phosphatidylcholine and Sphingomyelin are found on the ____ membrane, whereas Phosphatidylethanolamine and Phosphatidylserine are found on the ____ membrane.

    A) Inner (Intracellular), Outer (Extracellular).
    B) Outer (Extracellular), Inner (Intracellular).
    B) Outer (Extracellular), Inner (Intracellular).
  18. When might cell asymmetry be important?
    • Cell asymmetry is especially important in cell signalling.
    • Two examples of this are the action of Phosphokinase C and Phospholipase.
  19. What is the role of Phosphokinase C?
    Phosphokinase adds phosphates to phosphodatylinositol in order to promote other protein activity.
  20. What is the role of phospholipases?
    Phospholipases may also respond to extracellular stimulus. Phospholipases will cleave phospholipids bound with phosphates leaving a membrane bound fragment and another fragment to go and cause other effects.
  21. How is membrane asymmetry important to apoptosis?
    When a cell undergoes apoptosis, the phosphodatylserine molecules usually found on the cytosolic membrane translocate rapidly to the extracellular membrane. These can then be recognized by other cells.
  22. What are glycolipids?
    Glycolipids are Sugar Containing Molecules usually found in animal cells.
  23. What is the difference between Glycolipids and Gangliosides?
    Gangliosides contain Oligosaccharides with sialic acid residues giving them a negative charge.
  24. The following picture is could be an example of which type of membrane protein?
    A Transmembrane protein.
  25. Why do Transmembrane Proteins have to be amphiphilic?
    So they can interact with both the polar phosphate heads, and the hydrophobic hydrocarbon tails.
  26. Not all membrane proteins span the entire bilayer. Of those that don't, how might they be anchored in the membrane?
    • An Alpha Helix anchor could be embedded into one leaflet.
    • A covalently attached lipid chain could serve to anchor the protein to the membrane.
    • Similar to the above, some proteins will attach to phosphodatylinositol covalently.