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Questions and Answers
What is the primer molecule for the synthesis of long-chain fatty acids having an odd number of carbon atoms?
What is the primer molecule for the synthesis of long-chain fatty acids having an odd number of carbon atoms?
What is the primary source of NADPH for lipogenesis?
What is the primary source of NADPH for lipogenesis?
In which cellular compartment do the metabolic pathways of lipogenesis and the pentose phosphate pathway occur?
In which cellular compartment do the metabolic pathways of lipogenesis and the pentose phosphate pathway occur?
What is the role of NADPH in fatty acid synthesis?
What is the role of NADPH in fatty acid synthesis?
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What is the product of the reaction catalyzed by the 'malic enzyme'?
What is the product of the reaction catalyzed by the 'malic enzyme'?
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What is the characteristic of fatty acid synthesis in mammals?
What is the characteristic of fatty acid synthesis in mammals?
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What is the role of acetyl-CoA in the synthesis of palmitate?
What is the role of acetyl-CoA in the synthesis of palmitate?
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What is the function of the pentose phosphate pathway in lipogenesis?
What is the function of the pentose phosphate pathway in lipogenesis?
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What is the role of electron-transferring flavoprotein in the reoxidation of FADH2 by the respiratory chain?
What is the role of electron-transferring flavoprotein in the reoxidation of FADH2 by the respiratory chain?
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What is the function of enoil-CoA hydratase in fatty acid beta-oxidation?
What is the function of enoil-CoA hydratase in fatty acid beta-oxidation?
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What is the coenzyme involved in the dehydrogenation of the 3-hydroxy derivative?
What is the coenzyme involved in the dehydrogenation of the 3-hydroxy derivative?
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What is the product of the cleavage reaction catalyzed by thiolase?
What is the product of the cleavage reaction catalyzed by thiolase?
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What is the net reaction catalyzed by acyl-CoA acetyltransferase (thiolase)?
What is the net reaction catalyzed by acyl-CoA acetyltransferase (thiolase)?
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What is the function of the trifunctional protein in fatty acid beta-oxidation?
What is the function of the trifunctional protein in fatty acid beta-oxidation?
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What is the result of repeating the four-step process of fatty acid beta-oxidation six more times?
What is the result of repeating the four-step process of fatty acid beta-oxidation six more times?
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What is the final destination of the acetyl-CoA produced in fatty acid beta-oxidation?
What is the final destination of the acetyl-CoA produced in fatty acid beta-oxidation?
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What is the role of FAD in the reoxidation of FADH2 by the respiratory chain?
What is the role of FAD in the reoxidation of FADH2 by the respiratory chain?
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What is the substrate for the enzyme β-hydroxyacyl-CoA dehydrogenase?
What is the substrate for the enzyme β-hydroxyacyl-CoA dehydrogenase?
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What is the immediate substrate for fatty acid synthesis?
What is the immediate substrate for fatty acid synthesis?
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What is the role of ATP in the carboxylation reaction of acetyl-CoA?
What is the role of ATP in the carboxylation reaction of acetyl-CoA?
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What is the function of biotin in the acetyl-CoA carboxylase enzyme?
What is the function of biotin in the acetyl-CoA carboxylase enzyme?
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What is the end product of the fatty acid synthesis pathway?
What is the end product of the fatty acid synthesis pathway?
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What is the structural feature of the acetyl-CoA carboxylase enzyme?
What is the structural feature of the acetyl-CoA carboxylase enzyme?
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What is the significance of the decarboxylation reaction in fatty acid synthesis?
What is the significance of the decarboxylation reaction in fatty acid synthesis?
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What is the role of Mn2+ in the fatty acid synthesis pathway?
What is the role of Mn2+ in the fatty acid synthesis pathway?
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What is the difference between the fatty acid synthesis pathway in bacteria and plants versus in animals?
What is the difference between the fatty acid synthesis pathway in bacteria and plants versus in animals?
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Study Notes
Fatty Acid Synthesis
- Palmitate is synthesized from acetyl-CoA and malonyl-CoA, with acetyl-CoA forming carbon atoms 15 and 16 of palmitate.
- The addition of subsequent C2 units is via malonyl-CoA.
- Propionyl-CoA acts as a primer for the synthesis of long-chain fatty acids with an odd number of carbon atoms, found in ruminant fat and milk.
NADPH and Lipogenesis
- NADPH serves as a donor of reducing equivalents in the reduction of 3-ketoacyl and 2,3-unsaturated acyl derivatives.
- The oxidative reactions of the pentose phosphate pathway are the chief source of hydrogen required for the reductive synthesis of fatty acids.
- Tissues specializing in active lipogenesis (liver, adipose tissue, and lactating mammary gland) possess an active pentose phosphate pathway.
- Both metabolic pathways are found in the cytosol of the cell, with no membranes or permeability barriers against the transfer of NADPH.
Fatty Acid Synthesis Reaction
- Fatty acid synthesis from acetyl-CoA and malonyl-CoA occurs by a series of reactions catalyzed by:
- 6 different enzymes plus a separate acyl carrier protein (ACP) in bacteria.
- Individual domains of a very large polypeptide that includes an ACP domain in mammals.
Evolution of Mammalian Fatty Acid Synthase
- Evolution of the mammalian fatty acid synthase has involved gene fusion.
Production of Malonyl-CoA
- The initial and controlling step in fatty acid synthesis is the production of malonyl-CoA.
- Bicarbonate as a source of CO2 is required in the initial reaction for the carboxylation of acetyl-CoA to malonyl-CoA in the presence of ATP and acetyl-CoA carboxylase.
- Acetyl-CoA carboxylase has a requirement for the vitamin biotin.
Fatty Acid Synthesis Pathway
- The pathway involves the input of acetyl-CoA, which is carboxylated to malonyl-CoA.
- The reaction takes place in two steps: (1) carboxylation of biotin involving ATP and (2) transfer of the carboxyl to acetyl-CoA to form malonyl-CoA.
- ATP-dependent carboxylation provides energy input, and the CO2 is lost later during condensation with the growing fatty acid.
Dehydrogenation, Hydration, and Dehydrogenation
- Step 1: Dehydrogenation of alkane to alkene is catalyzed by isoforms of acyl-CoA dehydrogenase.
- Step 2: Hydration of alkene is catalyzed by two isoforms of enoyl-CoA hydratase.
- Step 3: Dehydrogenation of alcohol is catalyzed by β-hydroxyacyl-CoA dehydrogenase.
- Step 4: Transfer of fatty acid chain is catalyzed by acyl-CoA acetyltransferase (thiolase) via a covalent mechanism.
Fatty Acid Catabolism for Energy
- Repeating the four-step process six more times results in the complete oxidation of palmitic acid into eight molecules of acetyl-CoA.
- FADH2 and NADH are formed in each cycle, and acetyl-CoA enters the citric acid cycle and is further oxidized into CO2, producing more GTP, NADH, and FADH2.
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Description
This quiz covers the synthesis of palmitate from acetyl-CoA and malonyl-CoA, including the role of propionyl-CoA and the pentose phosphate pathway as a source of NADPH. It's a crucial topic in biochemistry and lipid metabolism.
