Lipids distribution in biological membranes is non-random and asymmetric. In eukaryotic cells, the cytoplasmic surface is enriched in anionic and primary amine-containing phospholipids (phosphoinositides (PIP), phosphatidic acid, phosphatidylethanolamine (PE), phosphatidylserine (PS)), whereas the extracytoplasmic leaflet and the surface of internal organelles are enriched in choline-containing phospholipids (phosphatidylcholine (PC) and sphingomyelin) and glycosphingolipids. In prokaryotic cells, PE is enriched in the cytoplasmic leaflet of the plasma membrane, phosphatidylglycerol (PG) is localized predominantly to the outer leaflet, and cardiolipin (CL) has a symmetric transbilayer distribution. Lipid asymmetry is generated and maintained by bi-directional transport (flip-flop) of lipids between the leaflets. This generation of asymmetry cannot be explained by sideness of lipids or by spontaneous transport alone. Specific membrane proteins, termed lipid flippases, play an essential role in this transport process. Lipid transport is required for triggering membrane-associated events such as blood coagulation, apoptosis, and signal transduction. Lipid transporters can be divided into flippases which transfer lipids towards cytoplasmic face, floppases which transfer lipids towards extracytoplasmic face, and scramblases that have bidirectional transport activity. Energy-independent flippases allow common phospholipids to equilibrate rapidly between the two monolayers and also play a role in the biosynthesis of a variety of glycoconjugates. ATP-dependent flippases, including members of a conserved subfamily of P-type ATPases and ATP-binding cassette transporters, mediate the net transfer of specific phospholipids to one leaflet of a membrane and are involved in the creation and maintenance of transbilayer lipid asymmetry of membranes such as the plasma membrane of eukaryotes and synthesis of lipopolysaccharide in prokaryotes
Name of the Student: Niyati s. Sharma
Reg No:1741210012
Batch: M.Tech II Year
Name of the Guide: Dr. Devi A.