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Chapter 9: Problem 6

Discuss the effects on the lipid phase transition of pure dimyristoyl phosphatidylcholine vesicles of added (a) divalent cations, (b) cholesterol, (c) distearoyl phosphatidylserine, (d) dioleoyl phosphatidylcholine, and (e) integral membrane proteins.

Short Answer

Expert verified
The phase transition of lipid vesicles can be influenced by various factors: Divalent cations and cholesterol decrease the phase transition temperature, whereas distearoyl phosphatidylserine increases it. Dioleoyl phosphatidylcholine and integral membrane proteins introduce irregularities in the packing of the lipid bilayer, thus usually decreasing the phase transition temperature.

Step by step solution

01

Effects of Divalent Cations

Divalent cations, such as calcium or magnesium, can form coordinate covalent bonds with the phosphate groups in the lipid head, aiding in condensation and hence, causing lowering of the phase transition temperature.
02

Effects of Cholesterol

Cholesterol can intercalate between the fatty acid chains of the lipid vesicle, disrupting their regular packing and hence, increasing the fluidity. This tends to decrease the phase transition temperature.
03

Effects of Distearoyl Phosphatidylserine

Distearoyl phosphatidylserine is a lipid with longer fatty acid chains. When incorporated into the vesicle, it strengthens van der Waals interactions, increasing the rigidity of the membrane and hence, raising the phase transition temperature.
04

Effects of Dioleoyl Phosphatidylcholine

Dioleoyl phosphatidylcholine is a lipid characterized by unsaturated fatty acid chains. The presence of double bonds introduces kinks into the fatty acid chains and disrupts their packing, hence increasing fluidity and lowering the phase transition temperature.
05

Effects of Integral Membrane Proteins

Integral membrane proteins span the entire bilayer and can disrupt the regular packing of the lipid molecules, adding to the fluidity. This tends to decrease the phase transition temperature.

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Most popular questions from this chapter

(Integrates with Chapter 3 .) Fructose is present outside a cell at \(1 \mu M\) concentration. An active transport system in the plasma membrane transports fructose into this cell, using the free energy of ATP hydrolysis to drive fructose uptake. What is the highest intracellular concentration of fructose that this transport system can generate? Assume that one fructose is transported per ATP hydrolyzed; that ATP is hydrolyzed on the intracellular surface of the membrane; and that the concentrations of ATP, ADP, and \(P_{i}\) are \(3 \mathrm{m} M, 1 \mathrm{m} M,\) and \(0.5 \mathrm{m} M,\) respectively. \(T=298 \mathrm{K}\). (Hint: Refer to Chapter 3 to recall the effects of concentration on free energy of ATP hydrolysis.)

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