Problem Set 7: Lipids and the Membrane

Due: Wednesday, 26 April 2023, 7:00 PM
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General Instructions

  1. This is a group activity. 
  2. Answer the problems found below.
  3. Submit your answers in pdf/jpg formats only following the naming, Chem40_PS7_<Section>_<Group No.>
  4. Only one submission per group is needed. 

Problems

  1. What are essential fatty acids?
  2. Predict the effects of the following on the phase transition temperature (Tm), and phospholipid fluidity of pure dipalmitoylphosphatidylcholine vesicles. Tm =45oC
    • Raising the temperature from 30oC to 50oC
    • Introducing dipalmitoleylphosphatidylcholine to the vesicles
    • Introducing dimyristoylphosphatidylcholine to the vesicles
    • Introducing cholesterol into the vesicles at 37oC
    • Incorporating integral membrane proteins into the vesicles
    • Changing ion concentration of the solution
  3. Triacylglycerols do not occur as components of membranes. Why?
  4. Identify the (a) nonpolar component(s) (b) polar component(s) and (c) if this component is what type of phospholipid.
  5. For a given membrane, the composition of which is given below:
    • phosphatidyl choline (PC)
    • phosphatidyl inositol (PI)
    • anion channels
    • phosphatidic acid (PA)
    • adenyl cyclase. (AC)
    • insulin receptor
    • Indicate whether these components are found in the outer (external half) or inner (cytoplasmic) half of the bilayer, or if it is a transmembrane component.
  6. What is the difference between a proteoglycan and a glycoprotein?  Answer briefly.
  7. Membrane vesicles of E. coli that possess the lactose permease (transporter of lactose) are loaded with KCl solution and are suspended in NaCl solution of equal concentration. It was observed that the vesicles actively, although transiently accumulated lactose when valinomycin was added to the suspension. No such active uptake was observed when NaCl was replaced by KCl in the suspending medium. Explain.
  8. How do the following cause cell death?
    • detergent
    • valinomycin
    • quabain
    • hypotonic solutions
  9. Why is glucose transport inhibited when the Na+-K+-ATPase pump is inhibited?
  10. How is transport of cytoplasmic NADH electrons (hydrides) across the very selective mitochondrial membrane made possible?