All are true about fatty acid synthesis except

DE NOVO SYNTHESIS OF FATTY ACIDS The process of fatty acid synthesis was studied by Feodor Lynen, who got Nobel prize in 1964. The pathway is referred to as Lynn&;s spiral. It is not a reversal of oxidation. Fatty acids are synthesized mainly by a de novo synthetic pathway operating in the cytoplasm. So it is referred to as extramitochondrial or cytoplasmic fatty acid synthase system. The major fatty acid synthesised de novo is palmitic acid, the 16C saturated fatty acid. The process occurs in liver, adipose tissue, kidney, brain, and mammary glands. Transpo of Acetyl CoA to Cytoplasm The staing material for de novo synthesis is acetyl CoA. It is formed inside the mitochondria from pyruvate. The inner membrane is not freely permeable to acetyl CoA. Hence the acetyl CoA units are delivered to the cytoplasm as citrate Citrate is transpoed from mitochondria by a tricarboxylic acid transpoer. In the cytoplasm, citrate is cleaved to oxaloacetate and acetyl CoA. The enzyme is ATP citrate lyase. The oxaloacetate can return to the mitochondria as malate or pyruvate net reaction of de novo synthesis of fatty acid may be summarized as 1 Acetyl CoA + 7Malonyl CoA +14NADPH +14H+ - 1Palmitate + 7CO2 +14NADP+ + 8CoA+ 6H2O Fatty acid synthesis is not an exact reversal of beta-oxidation. Co-enzymes of Fatty Acid Synthesis An impoant point to remember is that the co-enzyme utilised for de novo synthesis is NADPH. The sources of NADPH for fatty acid synthesis are 1. Pentose Phosphate Pathway This is the main source. Tissues having active lipogenesis (liver, adipose tissue, lactating mammary gland) have an active HMP shunt pathway also. 2. Malic Enzyme Malate + NADP+ - Pyruvate + CO2 + NADPH + H+ The reaction also helps to transfer cytoplasmic oxaloacetate to the mitochondria. For every molecule of acetyl CoA delivered to the cytoplasm, one molecule of NADPH is formed and reducing equivalents are generated in cytoplasmRef: DM Vasudevan - Textbook of Biochemistry, 8th edition, page no: 136-139