role of malonyl coa in fatty acid synthesis
chain elongation
title: Malonyl-CoA text: Malonyl-CoA Malonyl-CoA is a coenzyme A derivative of malonic acid. It plays a key role in chain elongation in fatty acid biosynthesis and polyketide biosynthesis. In the former, it provides 2-carbon units to fatty acids and commits them to fatty acid chain synthesis. Malonyl-CoA is formed by carboxylating acetyl-CoA using the enzyme acetyl-CoA carboxylase. One molecule of acetyl-CoA joins with a molecule of bicarbonate, requiring energy rendered from ATP. Malonyl-CoA is utilised in fatty acid biosynthesis by the enzyme malonyl coenzyme A:acyl carrier protein transacylase (MCAT). MCAT serves to transfer malonate from malonyl-CoA to the terminal thiol of "holo"-acyl carrier title: Fatty acid synthesis text: glucose. Regulation Acetyl-CoA is formed into malonyl-CoA by acetyl-CoA carboxylase, at which point malonyl-CoA is destined to feed into the fatty acid synthesis pathway. Acetyl-CoA carboxylase is the point of regulation in saturated straight-chain fatty acid synthesis, and is subject to both phosphorylation and allosteric regulation. Regulation by phosphorylation occurs mostly in mammals, while allosteric regulation occurs in most organisms. Allosteric control occurs as feedback inhibition by palmitoyl-CoA and activation by citrate. When there are high levels of palmitoyl-CoA, the final product of saturated fatty acid synthesis, it allosterically inactivates acetyl-CoA carboxylase to prevent a build-up of fatty acids in title: Fatty acid synthesis text: Fatty acid synthesis Fatty acid synthesis is the creation of fatty acids from acetyl-CoA and NADPH through the action of enzymes called fatty acid synthases. This process takes place in the cytoplasm of the cell. Most of the acetyl-CoA which is converted into fatty acids is derived from carbohydrates via the glycolytic pathway. The glycolytic pathway also provides the glycerol with which three fatty acids can combine (by means of ester bonds) to form triglycerides (also known as "triacylglycerols" – to distinguish them from fatty "acids" – or simply as "fat"), the final product of the lipogenic process. When only title: Malonyl-CoA decarboxylase text: natural kingdoms there is no scientific evidence to prove it. Malonyl-CoA is an important metabolite in some parts of the cell. In peroxisomes, the accumulation of this substance causes malonic aciduria, a highly pathogenic disease. To avoid it malonyl-CoA decarboxylase (MCD) converts malonyl-CoA into acetyl-CoA through the following reaction: In the cytosol, malonyl-CoA can inhibit the entrance of fatty acids into the mitochondria and it can also act as a precursor for the fatty acids synthesis. Malonyl-CoA also plays an important role inside the mitochondria, where it is an intermediary between fatty acids and acetyl-CoA, which will be a reserve title: Fatty acid text: cytosol where the synthesis of fatty acids occurs. This cannot occur directly. To obtain cytosolic acetyl-CoA, citrate (produced by the condensation of acetyl-CoA with oxaloacetate) is removed from the citric acid cycle and carried across the inner mitochondrial membrane into the cytosol. There it is cleaved by ATP citrate lyase into acetyl-CoA and oxaloacetate. The oxaloacetate is returned to the mitochondrion as malate. The cytosolic acetyl-CoA is carboxylated by acetyl CoA carboxylase into malonyl-CoA, the first committed step in the synthesis of fatty acids. Malonyl-CoA is then involved in a repeating series of reactions that lengthens the growing fatty acid