Practice question

Spontaneous assembly and healing of lipid bilayers arises from hydrophobic effect, fundamentally entropic driving force where water molecules form highly ordered clathrate-like cages around exposed hydrocarbon, reducing entropy of system. Aggregating acyl chains releases ordered water, increasing bulk water entropy and lowering overall Gibbs free energy by approximately 5 kJ per methylene group, favoring self-association. Van der Waals interactions between parallel acyl chains contribute additional enthalpic stabilization. If membrane suffers pore or tear exposing hydrocarbon edge to water, line tension at edge with exposed aliphatic chains contacting water is thermodynamically highly unfavorable, prompting rapid lateral flow of neighboring phospholipids to seal defect within milliseconds, minimizing hydrocarbon-water contact, process occurring without enzymatic assistance or ATP consumption. This self-repair underlies liposome formation when phospholipids are hydrated and vortexed, recovery after mechanical shearing and electroporation, and fusion of synaptic vesicles where stalk intermediates resolve to maintain continuity. High melting temperature would rigidify chains hindering closure, indicating hydrophobic interactions provide intrinsic resilience essential for maintaining barrier during stress and movement.