34. Kevin Ahern's Biochemistry - Metabolism of Membrane Lipids

1. Brown fat contains a protein called Uncoupling Protein that can insert itself into the mitochondrial inner membrane and allow protons to flow into the matrix, bypassing complex V. The protein does this to general heat and this may be important in keeping cells of the central nervous system warm. Glycerolipid and Sphingolipid Metabolism 1. Phosphatidic acid is an immediate precursor of CDP-diacylglycerol, which is a precursor of the various glycerophospholipids . CTP combines with phosphatidic acid to yield a pyrophosphate and CDP-Diacylglycerol. Activation by CDP yields a high energy activated intermediate that can be readily converted to phosphatidyl glycerophospholipids. 2. From CDP-diacylglycerol, phosphatidyl serine can be made, as can phosphatidyl ethanolamine and phosphatidyl choline. Synthesis of phosphatidyl choline from phosphatidyl ethanolamine requires methyl groups donated by S-Adenoysyl-Methionine (SAM). Loss of the methyl groups by SAM yields S-Adenosyl-Homocysteine (I incorrectly said S-adenosyl-homoserine in the lecture). 3. Phosphatidyl ethanolamine (and phosphatidyl choline - derived from phosphatidyl ethanolamine) can both be made independently of phosphatidic acid biosynthesis. For this pathway, CDP-ethanolamine is the activated intermediate and the phosphoethanolamine of it is added to diacylglycerol to form phosphatidylethanolamine. 4. Sphingolipids are synthesized beginning with palmitoyl-CoA and serine. Addition of a fatty acid to the amine...