Practice question

Intrinsic lipid curvature concept explains membrane remodeling during endocytosis exocytosis and organelle shaping. Lipid shape analyzed via Israelachvili packing parameter p equals v over a times l where v volume tail a head area l length: cylindrical p approximately one forms flat bilayers as phosphatidylcholine with two acyl chains head size similar to tail cross-section; conical p greater than one small head large tails such as phosphatidylethanolamine and diacylglycerol tends negative curvature monolayers bending toward water favoring inverted hexagonal HII phase; inverted conical p less than one third large head single chain lysophosphatidylcholine tends positive curvature micelles. PE ethanolamine headgroup small poorly hydrated versus two bulky eighteen carbon tails diacylglycerol causes conical geometry inducing negative spontaneous curvature stabilizing fusion intermediates stalk formation where contacting monolayers merge reducing fusion barrier energy estimated twenty to forty kilocalories. Concentrated inner leaflet at sites synapse vesicle budding, nuclear pore formation, facilitated by BAR and ENTH domains sensing curvature. Thus conical PE contributes curvature elasticity vital for dynamic remodeling and fusion competence.