HELP!!! Need answer asap...detailed calculations please!

Question

QUESTION: If a lipid raft is typically 70 nm in diameter and each lipid molecule has a diameter of 0.5 nm, about how many lipid molecules would there be in a lipid raft composed entirely of lipid? At a ratio of 50 lipid molecules per protein molecule (50% protein by mass), how many proteins would be in a typical raft? Explain. (Neglect the loss of lipid from the raft that would be required to accommodate the proteins).

Answer 1

This is actually a math problem disguised as a biology problem. A lipid raft that is 70 nm in diameter is 35^2 x pi = 3848.451 nm^2 in area. If each lipid molecule has a diameter of 0.5 nm, then it requires an area of 0.25^2 x pi = 0.196 nm^2. Thus, one can fit 3848.451 / 0.196 = 19600 lipid molecules per membrane leaflet (i.e. lipid layer) of the lipid raft or 39200 lipid molecules per lipid bi-layer in the lipid raft. If there is a 50:1 lipid to protein ratio, and we are allowed to neglect the loss of lipids required to fit the protein molecules into the same area, then there are 39200 / 50 = 784 protein molecules. If the 50:1 ratio is referring the to ratio of lipids in a single lipid layer to proteins (i.e. if the proteins all span the membrane) then 19600 / 50 = 392 protein molecules.