It's one of the components of the phospholipid bilayer. A phospholipid has a hydrophilic (polar) head and 2 hydrophobic (non-polar) tails. Due to this biochemistry, the preferred conformation for these phospholipids is to form a phospholipid bilayer. This is comprised of 2 layers of phospholipids where the polar heads face the water and the non-polar tails face each other .
- ↑ Alberts, B. Bray, D. Hopkin, K. Johnson, A. Lewis, J. Raff, M. Roberts, K. Walter, P. (2013) Essential Cell Biology, 4th Edition, United States: Garland Science, Chapter 2, Page 55