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areal density and mean spacing

The area fraction associated with membrane proteins in the red blood cell (diameter = 8 µm) membrane is roughly 23%, while the lipids themselves take up roughly 77% of the membrane area.

a.Approximately how many phospholipids make up the red blood cell membrane?

b.How many membrane proteins would you estimate are in the red blood cell membrane

c.What is their mean spacing?


Solution Preview

We are given the diameter of a red blood cell as 8 µm (so radius of 4 µm), and the proportion of the membrane that is lipids vs proteins.

To go from a proportion to an absolute number, we'll need to find out the total area of the red blood cell, as well as the area taken up by each component.

Finding the surface area of the red blood cell is a geometry problem that requires some assumptions as to the shape of the red blood cell. As you may know, in real life red blood cells are disks with indents on either side, which makes them a bit of a complicated shape to get the area from just the radius. If you're interested, there is a paper by Deuling and Helfrich (Biophysical Journal 16(8) pp 861-868) describing the formulas that closely approximate a red blood cell. With those and no small measure of calculus, you can find the surface area.

A more reasonable approach is to make an assumption as to whether the red blood cell more closely approximates a sphere or a disk. I might ...

Solution Summary

The areal density and mean spacing are investigated.