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Chapter 9: Problem 2

The purple patches of the Halobacterium halobium membrane, which contain the protein bacteriorhodopsin, are approximately \(75 \%\) protein and \(25 \%\) lipid. If the protein molecular weight is 26,000 and an average phospholipid has a molecular weight of 800 , calculate the phospholipid-to-protein mole ratio.

Short Answer

Expert verified
The phospholipid-to-protein mole ratio in the Halobacterium halobium membrane is approximately 10.84.

Step by step solution

01

Determining the percentage in moles

First, let's consider 100 g of membrane. In this case, 75 g will be protein and 25 g will be lipid. To find the quantity in moles, we must divide these values by the respective molecular weights. Therefore, protein moles = 75 g / 26,000 g/mole = 0.002884615 mole. Similarly, lipid moles = 25 g / 800 g/mole = 0.03125 mole.
02

Calculating the phospholipid-to-protein mole ratio

The phospholipid-to-protein mole ratio can now be calculated by dividing the number of lipid moles by the number of protein moles. That is, phospholipid-to-protein mole ratio = 0.03125 mole / 0.002884615 mole = 10.84 approximately.

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Most popular questions from this chapter

Sucrose gradients for separation of membrane proteins must be able to separate proteins and protein-lipid complexes having a wide range of densities, typically 1.00 to \(1.35 \mathrm{g} / \mathrm{mL}\) a. Consult reference books (such as the CRC Handbook of Biochemistry \()\) and plot the density of sucrose solutions versus percent sucrose by weight (g sucrose per 100 g solution), and versus percent by volume (g sucrose per \(100 \mathrm{mL}\) solution). Why is one plot linear and the other plot curved? b. What would be a suitable range of sucrose concentrations for separation of three membrane-derived protein-lipid complexes with densities of \(1.03,1.07,\) and \(1.08 \mathrm{g} / \mathrm{mL} ?\)

As described in the text, the \(\mathrm{pK}_{\mathrm{a}}\) values of Asp \(^{85}\) and \(\mathrm{Asp}^{96}\) of bacteriorhodopsin are shifted to high values (more than 11 ) because of the hydrophobic environment surrounding these residues. Why is this so? What would you expect the dissociation behavior of aspartate carboxyl groups to be in a hydrophobic environment?

As described in this chapter, proline introduces kinks in transmembrane \(\alpha\) -helices. What are the molecular details of the kink, and why does it form? A good reference for this question is von Heijne, G. 1991\. Proline kinks in transmembrane \(\alpha\) -helices. Journal of Molecular Biology \(218: 499-503 .\) Another is Barlow, D. \(\mathrm{J}\)., and Thornton, J. M., \(1988 .\) Helix geometry in proteins. Journal of Molecular Biology \(201: 601-619\)

In this chapter, we have examined coupled transport systems that rely on ATP hydrolysis, on primary gradients of \(\mathrm{Na}^{+}\) or \(\mathrm{H}^{+},\) and on phosphotransferase systems. Suppose you have just discovered an unusual strain of bacteria that transports rhamnose across its plasma membrane. Suggest experiments that would test whether it was linked to any of these other transport systems.

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.
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