Membrane fluidity is the property of a phospholipid bilayer describing the freedom of its constituent molecules to move relative to one another, and it is governed by a single unifying mechanism: the average spacing between adjacent phospholipids, with greater intermolecular distance corresponding to greater fluidity and tighter packing to lower fluidity. Three determinants act through this mechanism — thermal energy, which increases molecular motion and spacing as temperature rises and permits a crystallized, tightly packed state at low temperature; cholesterol, which behaves as a bidirectional buffer by spacing phospholipids apart at low temperature and restraining them at high temperature; and fatty-acid saturation, where the kinks introduced by double bonds in unsaturated chains prevent the neat stacking achieved by straight saturated chains. The concept belongs to cell biology and membrane biophysics, and it grounds the discipline's account of how a cell preserves membrane integrity and function across a range of environmental temperatures.
Membrane fluidity is the property of a phospholipid bilayer describing the freedom of its constituent molecules to move relative to one another, and it is governed by a single unifying mechanism: the…