# How to calculate Protein & Lipid molecules

Jonathan Walker walker at carina.nrl.navy.mil
Mon Mar 13 09:19:35 EST 1995

```Hello,

My background in Lipid, Protein, & Bilayers in Red Cells
is not well versed.  However, I'm trying to calculate the following:

1) I have a (human) red cell membrane approx. 8nm thick
2) The cell contains 5.2 x 10^-13 grams of lipid
(10^-13 = ten to the minus thirteen)
3) Also, the cell contains 6.0 x 10^-13 grams of protein.
4) The lipid has primarily phospholipid (MW 800) & cholestrol (MW386)
in a 1:1 molar ratio.
5) Each phospholipid occupies a surface area of  0.55nm^2 per molecules
6) While, the cholesterol occupies a surface area of 0.38nm^2 per molecules
7) The red cell has a surface area of 145um^2.

Questions:

1) If we assume an average protein has a molecular weight of 50,000,
how many molecules of protein are in a single red cell membrane?

2) What is the ratio of lipid molecules to protein molecules in the
red cell membrane??

3) What proportion of the total surface area of the membrane is occupied
by a lipid bilayer???