The effects of temperature on biological membranes and their models

The physical effects of temperature on biological membranes are reviewed. Our current understanding of membrane structure is based on a model in which proteins are inserted in or are attached to a lipid bilayer structure. The lipid composition varies between cell types. Phospholipid bilayers undergo phase transitions at temperatures which are dependent on chain length and the structure of the headgroup. These factors also affect the miscibility of phospholipid types. Cholesterol orders the phospholipid chains above their phase transition temperature but disorders them below this temperature. Cerebrosides, which are important constituents of the myelin membrane, form metastable states under certain conditions. The activities of membrane-bound enzymes may be affected by the physical state of the lipid bilayer which, in turn, is affected by temperature. The interactions between the lipid and protein components of membranes have been investigated by a variety of techniques.