3 Acetyl CoA carboxylase is active in a polymeric state The equilibrium between

3 acetyl coa carboxylase is active in a polymeric

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3. Acetyl-CoA carboxylase is active in a polymeric state. The equilibrium between active polymer and inactive protomers is affected by citrate and palmitoyl-CoA. Citrate is an allosteric activator of the enzyme and shifts the equilibrium to the polymer. Palmitoyl-CoA shifts the equilibrium to the inactive, protomeric state. The enzyme is phosphorylated by a number of kinases and the phosphorylated state has a low affinity for citrate and a high affinity for palmitate. 4. a. 3; b. 6; c. 2; d. 4; e. 1; f. 5. 143
Chapter 24 · Lipid Biosynthesis 5. b. B; d. H; f. H; g. V; h. H; j. B; k. H. 6. The production 3 R -mevalonate from HMG-CoA catalyzed by HMG-CoA reductase. 7. a. 2; b. 4; c. 1; d. 3. 8. Dihydroxyacetone phosphate is converted to 1-acyldihydroxyacetone-phosphate by anacyltransferase reaction and reduced to 1-acylglycerol-3-phosphate by a reductase. Thiscompound can also be synthesized from glycerol-3-phosphate by acyltransferase. Transfer ofa second acyl group to C-2 produces phosphatidic acid whose structure is shown below.R1COOCH2COCHCH2OCOO-O-R2O9. The head groups of phosphatidylethanolamine and phosphatidylcholine derive fromcytidine diphosphate derivatives. CDP-diacylglycerol is a precursor of phosphatidylinositol,phosphatidylglycerol, and cardiolipin.10. Hormones; arachidonic acid; linoleic acid.Additional Problems1. What are the sources of carbons for fatty acid biosynthesis? What is the role of the citrate-malate-pyruvate shuttle in making carbon compounds available for fatty acid biosynthesis?2. Movement of citrate out of the mitochondria coordinates glycolysis and fatty acidbiosynthesis. Explain.3. Name the three water soluble vitamins that are crucial to fatty acid synthesis and brieflydescribe the roles they play in this process.4. Why do mammals require certain essential fatty acids in their diet? 5. Outline the synthesis of glycerophospholipid.6. Lovastatin lowers serum cholesterol by interfering with HMG-CoA reductase, the enzymethat catalyzes the rate limiting step in cholesterol synthesis. The drug is administered as aninactive lactone that is activated by hydrolysis to mevinolinic acid, a competitive inhibitor ofHMG-CoA reductase. Can you recall another lactone hydrolysis reaction encountered in anearlier chapter?7. What is the role of high-density lipoproteins in regulation of cholesterol levels in the blood?8. Synthesis of the steroid hormones from cholesterol starts with the reaction catalyzed bydesmolase shown below. Why is this a critical reaction for formation of steroid hormones? 144
Chapter 24 · Lipid Biosynthesis H 3 C H 3 C HO H 3 C H 3 C HO O C O H Isocaproic aldehyde Pregnenolone Cholesterol Abbreviated Answers

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