Which of the following best describes lipid bilayer asymmetry?
Transverse asymmetry arises because lipid synthesis and active transport are polarized across bilayer and maintained continuously by energy-dependent enzymes. In ER, phosphatidylcholine is produced by CDP-choline pathway and partly enriches outer leaflet after vesicular trafficking, while phosphatidylserine synthesized by serine exchange enzymes PSS1 and PSS2 remains preferentially cytosolic. P4-ATPase flippases ATP11C and ATP8A1 hydrolyze ATP to move phosphatidylserine and phosphatidylethanolamine inward against gradient, while ABC floppases like ABCB4 and ABCC1 move phosphatidylcholine and c
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 10: Lipid Asymmetry and Flippases.