Question

The density of the plasma membrane of a cell was found to be 1.07 g/mL. If the density of the lipid component is 0.91 g/mL and the density of the protein component is 1.36 g/mL, what is the percent composition (to the nearest ones) of the lipid component of the membrane, assuming the plasma membrane consists only of the lipid and protein components?

Answer 1

Let volume of lipid part = V1

Mass = volume x density = 0.91 V1

volume of protein part = V2 ,

mass of protien part = 1.36V2

total plasma volume = V1+V2 ,

mass of plasma = 1.07 ( V1+V2)

Mass of lipid + Mass of protien = mass of plasma

0.91V1 + 1.36 V2 = 1.07 ( V1+V2)

0.16 V1 = 0.29 V2 , hence V1 = 1.8125 V2

plasma mass = 1.07V1 + 1.07V2 = 1.07 ( 1.8125V2) + 1.07V2 = 3V2

Mass percent of protein = 100 x ( protien mass / plasma mass)

                            = ( 1.36V2 /3V2) = 45 %

lipid % = 100 -45 = 55 %

                         = ( 0.91V1 / 1.07V1 + 1.07 (