Theoretical phase diagram for a binary mix of a single lipid species with cholesterol (after Ipsen et al., 1987) . For a thorough update on current knowledge of phase behaviour in modelled biological membranes, readers are invited to turn to the recent article by de Almeida et al. . Ld: Liquid disorganised phase Lo: Liquid organised phase (because cholesterol can act as a spacer, molecules are more densely packed together, and impose more rigid conformations on one another. There is an increased thickness of the membrane, but the average speed of molecules is comparable to that seen in the Ld phase.) For both these liquid phases, the thermal energy of individual molecules is superior to the one resulting from their interaction with their neighbours. There is therefore no privileged interactions between individual molecules So: Solid phase. The molecules develop privileged interactions with their neighbours, resulting in stable arrangements that can lead to long lasting structures of crystalline nature.
Joly BMC Cell Biology 2004 5:3 doi:10.1186/1471-2121-5-3