Practice question

Maintenance high curvature membranes such as thirty nanometer synaptic vesicles tubular ER sheets requires conical lipids complementing protein scaffolds BAR ENTH and reticulons. Phosphatidylethanolamine ethanolamine headgroup cross section smaller than diacylglycerol tail volume adopts molecular cone favoring negative mean curvature concave cytosolic leaflet facilitating fission fusion stalk formation hemifusion diaphragm expansion. Synthesis via Kennedy pathway CDP ethanolamine ethanolamine phosphotransferase EPT1 and mitochondrial phosphatidylserine decarboxylase PSD converting PS PE enriched contact sites generating local PE pools ER mitochondria associated membranes. Flippases ATP11 transport PE inward increasing inner leaflet concentration; BAR domain proteins amphiphysin endophilin sense curvature recruit dynamin for scission constriction. PE depletion knockdown PCYT2 impairs cytokinesis nuclear envelope breakdown Golgi fragmentation ER exit site formation. Cholesterol cylindrical near zero curvature does not generate curvature alone, sphingomyelin lamellar stabilizer prevents bending, phosphatidylinositol signaling mainly IP3 DAG generation not curvature. Hence PE uniquely supports curvature shape coupling reducing bending modulus twenty to ten kBT mechanism central organelle morphology questions examined cell biology biophysics and trafficking exams linking lipid shape physics biology membrane remodeling processes.