Practice question

Fluidity of biomembranes reflects balance between van der Waals cohesion and steric freedom of acyl chains introduced by kinks. Shortening fatty acid chains from eighteen to fourteen carbons reduces surface area for London dispersion forces, weakening chain chain attraction and lowering cooperative melting enthalpy and phase transition temperature. The transition temperature Tm drops sharply, so at physiological thirty seven degrees a larger fraction exists in liquid crystalline disordered state characterized by frequent trans gauche isomerizations and rapid lateral diffusion near ten to minus eight centimeters squared per second. Bacteria implement homeoviscous adaptation by inducing FabA FabB or desaturases DesA to synthesize shorter unsaturated chains when temperature falls, preserving optimal viscosity. In model liposomes DLPC twelve carbons shows Tm minus one versus DPPC sixteen carbons Tm forty one demonstrates principle quantitatively. Short chains also thin bilayer slightly increasing passive permeability to solutes. Cells compensate by increasing cholesterol and sphingomyelin. Mastering chain length fluidity relationship predicts how diet psychrophilic adaptation and anesthetics alter receptor function and transport kinetics in physiology questions.