(BQ) Part 2 book “Rapid review biochemistry” has contents: Lipid metabolism, nitrogen metabolism, integration of metabolism, nucleotide synthesis and metabolism, gene expression, organization, synthesis, and repair of DNA, DNA technology. | CHAPTER 7 LIPID METABOLISM I. Fatty Acid and Triacylglycerol Synthesis A. Overview 1. Fatty acid and triacylglycerol synthesis occurs in the cytoplasm (oxidation occurs in the mitochondria) but its precursor, acetyl CoA, is formed in the mitochondrial matrix. 2. Fatty acid synthesis begins in the mitochondria with the formation of citrate as a 2-carbon transporter (acetyl CoA shuttle to cytoplasm). 3. Acetyl CoA carboxylase provides malonyl CoA to be used by the multienzyme complex, fatty acid synthase. 4. Regulation of fatty acid synthesis occurs at acetyl CoA carboxylase and is controlled by insulin, glucagon, and epinephrine. 5. Many phospholipids are derived from desaturated fatty acids, most of which are synthesized by the body. B. Fatty acid and triacylglycerol synthesis: pathway reaction steps (Fig. 7-1) 1. Step 1 a. The citrate shuttle transports acetyl CoA generated in the mitochondrion to the cytosol (see Fig. 7-1). b. Acetyl CoA cannot move across the mitochondrial membrane and must be converted into citrate. c. Acetyl CoA and oxaloacetate (OAA) undergo an irreversible condensation by citrate synthase to form citrate, which is transported across the mitochondrial membrane into the cytosol. d. Citrate remaining in the mitochondrion is used in the citric acid cycle. 2. Step 2 a. Citrate is converted back to acetyl CoA and OAA by citrate lyase, an insulinenhanced enzyme, in a reaction that requires ATP. 3. Step 3 a. Acetyl CoA is converted to malonyl CoA (see Step 5 below for disposal of OAA), an important intermediate in fatty acid synthesis, by acetyl CoA carboxylase in an irreversible rate-limiting reaction that consumes ATP and requires biotin as a cofactor. b. Malonyl CoA inhibits carnitine acyltransferase I (see fatty acid oxidation below), preventing movement of newly synthesized fatty acids across the inner mitochondrial membrane into the matrix, where fatty acids undergo b-oxidation (futile cycling is thereby avoided). 4. Step 4 a. Fatty acid .
