Hybrid cell membrane had initially distinct regions of green and red dye. In less than an hour, the two colors were intermixed. Some membrane proteins are tethered to the cytoskeleton and cannot move far. Membranes must be fluid to work properly. Solidification may result in permeability changes and enzyme deactivation.
Membranes solidify if the temperature decreases to a critical point.
Critical temperature is lower in membranes with a greater concentration of unsaturated phospholipids. More fluid at lower temperatures by preventing close packing of phospholipids. Cells may alter membrane lipid concentration in response to changes in temperature. Function A membrane is a mosaic of different proteins embedded and dispersed in the phospholipid bilayer.