Lipid Metabolism Essay

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Lipid Metabolism The basis of lipid metabolism starts with lipid catabolism, the breakdown of organic substrates, specifically via lipolysis in which lipids are broken down into pieces and then converted into pyruvic acid and channeled into the TCA or citric acid cycle. Through hydrolysis, a triglyceride is split into one molecule of glycerol and three fatty acid molecules. Glycerol is further broken down into dihydroxyacetone phosphate and then into pyruvic acid, both as a result of glycolysis. Fatty acids, on the other hand, are oxidized to acetyl coenzyme A (CoA) in the mitochondria. This occurs through a process known as beta-oxidation. An 18-carbon chain fatty acid is broken down into 2-carbon fragments. Just one step generates molecules of acetyl-CoA, NADH, and FADH2. And there is still a 16-carbon chain left. The cell can generate 144 ATP molecules from just one fatty acid molecule. Because fatty acids are oxidized inside the mitochondria, acetyl-CoA can enter the citric acid cycle immediately. Acetyl-CoA initiates the TCA cycle. Pyruvic acid, two 3-carbon molecules, reacts with NAD and CoA to produce CO2, NADH, and acetyl-CoA. The acetyl group is transferred from CoA to oxaloacetic acid to create citric acid (the 2-carbon acetyl group attaches to the 4-carbon molecule of oxaloacetic acid which begets the 6-carbon molecule of citric acid). Citric acid removes hydrogen ions from organic molecules and makes coenzymes. Citric acid then becomes isocitric acid. NAD removes hydrogen ions from isocitric acid and produces NADH and CO2 is removed via decarboxylation. Isocitric acid then becomes alpha-ketoglutaric acid. NAD removes hydrogen ions and succinyl CoA results. Succinyl CoA becomes succinic acid and GDP forms GTP. ATP is produced via substrate-level phosphorylation. GTP transfers a phosphate group to ADP top make ATP (GTP+ADP=GDP+ATP). FAD

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