The average molecular weight of protein is 50,000, average molecular weight of p

Question

The average molecular weight of protein is 50,000, average molecular weight of phospholipids is 800 and average molecular weight of cholesterol is 386. The ratio of mass of protein to phospholipids to cholesterol in human red blood cells (RBCs) is about 2: 1: 1. Number of lipid molecules (cholesterol + phospholipids) for every molecule of protein can be calculated as follows: Number of lipid molecules = (2/50,000)/(1/800 + 1/386) = 100 Hence, there are 100 molecules of lipids for every protein molecule.

Explanation / Answer

Let us consider 100 gm of membrane then for 2:1:1 ratio protein will be equal to 50 gm, phospholipid will be equal to 25 gm and cholesterol will be equal to 25 gm

Let A be the avogadro number
molecules of protein is A*no. of moles = 50/50000*A = 0.001 A
molecules of lipid is A*no. of moles of phospholipid + A*no. of moles of cholesterol = A* 25/800+ A*25/386 =0.096A
Hence there are 0.096A / 0.001 A = 96 molecules of lipids per molecule of protein

No of molecules of phospolipid = A*25/800 = 0.03125A

No of molecules of cholesterol = A*25/386 = 0.06476A

Hence there are 0.06476A/0.03125A = 2 molecules of cholesterol per molecule of phospolipid

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