Questions and Answers
Where does fatty acid oxidation occur in most eukaryotes?
What is the final product of thiolytic cleavage in the β-oxidation of odd-chain fatty acids?
What is the energy yield of fatty acid oxidation compared to glucose oxidation?
How many molecules of acetyl CoA are produced from the β-oxidation of stearate (18 C)?
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What is the intermediate formed during the conversion of propionyl CoA in mammals?
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Which type of fatty acid chains are usually synthesized by bacteria and some organisms?
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What is the process known as when the β-carbon unit (C-3) of the FA is being oxidized?
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What is produced during the oxidation of fatty acids and is utilized in the electron transport chain?
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What is the byproduct of the final step of β-oxidation?
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Where does β-oxidation occur in eukaryotes?
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What is the enzyme that catalyzes the formation of a double bond between C2 and C3 atoms of the acyl group?
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What is the product of the hydration step of β-oxidation?
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What is the electron carrier that receives electrons from acyl-CoA dehydrogenase?
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What is the acetyl-CoA used for in organisms that have the glyoxylate pathway?
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What is the role of fatty acid synthase inhibitors in mice?
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What is the function of lipoprotein lipase in triacylglycerol metabolism?
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What is the precursor of steroid hormones and bile salts in mammals?
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What is the result of inhibiting fatty acid synthase, at least in part?
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What is the function of β-oxidation in fatty acid metabolism?
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What is the role of chylomicrons in lipid transport?
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What is the source of all carbon atoms of cholesterol?
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What is the fate of glycerol released from triacylglycerol hydrolysis?
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Study Notes
Fatty Acid Oxidation
- Fatty acid oxidation occurs in two stages: activation of fatty acid and degradation of 2-carbon units.
- It is also known as β-oxidation, as the β-carbon unit (C-3) of the fatty acid is being oxidized.
β-Oxidation Process
- First step: Oxidation
- Acyl-CoA dehydrogenase catalyzes the formation of a double bond between C2 and C3 atoms of the acyl group, forming trans 2-enoyl CoA.
- Electrons from fatty acyl CoA are transferred to acyl CoA dehydrogenase electron-transferring flavoprotein (ETF) and then to ubiquinone (QH2).
- Second step: Hydration
- Water is added to trans 2-enoyl CoA, forming L-3-Hydroxyacyl CoA, catalyzed by 2-enoyl-CoA hydratase.
- Third step: Oxidation
- L-3-Hydroxyacyl CoA dehydrogenase catalyzes the formation of 3-ketoacyl CoA, using NAD+.
- NADH is used in the electron transport chain.
- Final step: Thiolysis
- The nucleophilic sulfhydryl group of HS-CoA attacks the carbonyl carbon of 3-ketoacyl CoA, releasing acetyl CoA and a fatty acid shorter by 2 carbons.
ATP Generation from Fatty Acid Oxidation
- Fatty acid oxidation supplies more energy than glucose oxidation.
- For example, stearate (18 C) is converted to stearoyl CoA using 2 ATP, and 9 molecules of acetyl CoA enter the TCA cycle, generating 10 ATP each through 8 cycles of β-oxidation.
β-Oxidation of Odd-Chain and Unsaturated Fatty Acids
- Most fatty acids have an even number of carbon units, but some bacteria and organisms synthesize odd-chain fatty acids.
- These fatty acids are oxidized the same way as even-chain fatty acids, except the final product of the thiolytic cleavage is propionyl CoA (CoA with C3 acyl group) rather than acetyl CoA.
- Propionyl CoA can be converted to succinyl CoA in mammals.
Lipid Transport and Synthesis
- Lipid digestion products are absorbed by the intestinal mucosa and converted to triacylglycerol, which is packed into lipoprotein particles called chylomicrons.
- Triacylglycerols synthesized by the liver are packed into very low-density lipoproteins (VLDL) and released into the blood.
- The triacylglycerol components of chylomicrons and VLDL are hydrolyzed to fatty acids and glycerol in the capillaries of adipose tissue and skeletal muscle by lipoprotein lipase.
Cholesterol Synthesis
- Steroid cholesterol is an essential component of many membranes and a precursor of steroid hormones and bile salts.
- All carbon atoms of cholesterol come from acetyl CoA.
- The stages of the cholesterol biosynthesis pathway involve the synthesis of cholesterol from acetyl CoA.
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Description
Learn about the two stages of fatty acid oxidation, activation and degradation, and the β-oxidation process, including the oxidation step and enzyme catalysis. Understand how fatty acyl CoA is converted to trans 2-enoyl CoA.
