The Solid-State Structure of Lipids

Abstract

It has been nearly 100 years since Overtone¹ found that the rates at which uncharged molecules pass through the membranes of plant cells are roughly correlated with the solubility of the same molecules in fats. He concluded that membranes are composed largely of lipids. In Figure 1 there are four representations of one type of lipid molecule — polar head group upmost with non-polar tails trailing downwards. Such molecules, containing both strongly hydrophobic and hydrophilic groups, are termed amphiphilic. Figure 2 shows the chemical structure of the main varieties of lipid found in the membranes of living cells. Depending on the origin of the cell, lipids contribute from ~20% to ~80% of the weight of the membrane². In the next few chapters we will be concerned almost exclusively with phospholipids, the properties of which are uncannily suited to building the thin, flexible, yet stable, barrier that separates the cell contents from the rest of the universe.