Erythrocytes Cell Membrane Lipids.

http://en.wikipedia.org/wiki/Red_blood_cell

The erythrocyte cell membrane comprises a typical lipid bilayer, similar to what can be found in virtually all human cells. Simply put, this lipid bilayer is composed of cholesterol and phospholipids in equal proportions by weight. The lipid composition is important as it defines many physical properties such as membrane permeability and fluidity. Additionally, the activity of many membrane proteins is regulated by interactions with lipids in the bilayer.

Unlike cholesterol, which is evenly distributed between the inner and outer leaflets, the 5 major phospholipids are asymmetrically disposed, as shown below:

Outer monolayer

• Phosphatidylcholine (PC);
• Sphingomyelin (SM).

Inner monolayer

• Phosphatidylethanolamine (PE);
• Phosphoinositol (PI) (small amounts).
• Phosphatidylserine (PS)