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Questions and Answers
What do chylomicron remnants and IDLs become enriched in after triglyceride deposition?
What do chylomicron remnants and IDLs become enriched in after triglyceride deposition?
Which lipoprotein is responsible for delivering cholesterol to peripheral tissues?
Which lipoprotein is responsible for delivering cholesterol to peripheral tissues?
What is the end product when all three ester bonds of a triglyceride are hydrolyzed?
What is the end product when all three ester bonds of a triglyceride are hydrolyzed?
Where does fatty acid oxidation primarily occur?
Where does fatty acid oxidation primarily occur?
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What must happen to fatty acids before $β$-oxidation can begin?
What must happen to fatty acids before $β$-oxidation can begin?
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What is the first step in the digestion of fatty acids in the mitochondrial matrix?
What is the first step in the digestion of fatty acids in the mitochondrial matrix?
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What can the glycerol molecule be phosphorylated into after triglyceride metabolism?
What can the glycerol molecule be phosphorylated into after triglyceride metabolism?
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What is the purpose of the carnitine shuttle in fatty acid metabolism?
What is the purpose of the carnitine shuttle in fatty acid metabolism?
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Which type of fatty acids can enter the mitochondrial matrix directly?
Which type of fatty acids can enter the mitochondrial matrix directly?
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Acyl-CoA is formed when fatty acids react with which molecule?
Acyl-CoA is formed when fatty acids react with which molecule?
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Which enzyme catalyzes the transfer of the acyl group from coenzyme A to carnitine?
Which enzyme catalyzes the transfer of the acyl group from coenzyme A to carnitine?
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Which of the following correctly describes acyl-CoA?
Which of the following correctly describes acyl-CoA?
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What is produced as a result of the first oxidation step in $β$-oxidation?
What is produced as a result of the first oxidation step in $β$-oxidation?
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During the $β$-oxidation process, what occurs after the formation of trans-enoyl-CoA?
During the $β$-oxidation process, what occurs after the formation of trans-enoyl-CoA?
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What happens to carnitine after it assists in transporting acyl groups into the mitochondrial matrix?
What happens to carnitine after it assists in transporting acyl groups into the mitochondrial matrix?
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Which enzyme is responsible for the reformation of acyl-CoA within the mitochondrial matrix?
Which enzyme is responsible for the reformation of acyl-CoA within the mitochondrial matrix?
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What is the primary purpose of gluconeogenesis in the liver?
What is the primary purpose of gluconeogenesis in the liver?
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What molecules do NADH and FADH2 produced in $β$-oxidation enter?
What molecules do NADH and FADH2 produced in $β$-oxidation enter?
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What is a significant outcome of excess acetyl-CoA produced during $β$-oxidation?
What is a significant outcome of excess acetyl-CoA produced during $β$-oxidation?
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Which enzyme catalyzes the condensation of two acetyl-CoA molecules to form acetoacetyl-CoA?
Which enzyme catalyzes the condensation of two acetyl-CoA molecules to form acetoacetyl-CoA?
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What distinguishes D-$β$-hydroxybutyrate from other ketone bodies?
What distinguishes D-$β$-hydroxybutyrate from other ketone bodies?
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What happens to D-$β$-hydroxybutyrate in other tissues after being transported from the liver?
What happens to D-$β$-hydroxybutyrate in other tissues after being transported from the liver?
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What is a consequence of high levels of acetone detected on the breath?
What is a consequence of high levels of acetone detected on the breath?
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Which of the following describes the transport mechanism of acetoacetate and D-$β$-hydroxybutyrate from liver to tissues?
Which of the following describes the transport mechanism of acetoacetate and D-$β$-hydroxybutyrate from liver to tissues?
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What is the role of enoyl-CoA isomerase in $β$-oxidation of unsaturated fatty acids with double bonds between odd and even-numbered carbons?
What is the role of enoyl-CoA isomerase in $β$-oxidation of unsaturated fatty acids with double bonds between odd and even-numbered carbons?
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What is acetoacetate converted into before undergoing beta-oxidation?
What is acetoacetate converted into before undergoing beta-oxidation?
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How does the presence of a double bond in fatty acids between odd and even-numbered carbons affect ATP production during $β$-oxidation?
How does the presence of a double bond in fatty acids between odd and even-numbered carbons affect ATP production during $β$-oxidation?
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During fasting, what primarily drives fatty acid oxidation?
During fasting, what primarily drives fatty acid oxidation?
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What is the consequence when a fatty acid contains a double bond between even and odd-numbered carbons?
What is the consequence when a fatty acid contains a double bond between even and odd-numbered carbons?
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Why can't acetyl-CoA freely cross the inner mitochondrial membrane?
Why can't acetyl-CoA freely cross the inner mitochondrial membrane?
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Which enzyme acts after acyl-CoA dehydrogenase when a fatty acid has double bonds between even and odd-numbered carbons?
Which enzyme acts after acyl-CoA dehydrogenase when a fatty acid has double bonds between even and odd-numbered carbons?
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What enzyme is responsible for splitting cytosolic citrate into acetyl-CoA and oxaloacetate?
What enzyme is responsible for splitting cytosolic citrate into acetyl-CoA and oxaloacetate?
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What enzyme converts the double bond in an odd-even arrangement from a cis to a trans configuration?
What enzyme converts the double bond in an odd-even arrangement from a cis to a trans configuration?
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Which of the following happens to cytosolic citrate in the well-fed state?
Which of the following happens to cytosolic citrate in the well-fed state?
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What is a consequence of using NADPH in the oxidation of fatty acids with even-odd carbon double bonds?
What is a consequence of using NADPH in the oxidation of fatty acids with even-odd carbon double bonds?
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Why can't the fatty acid with conjugated double bonds fit into the active site of enoyl-CoA hydratase?
Why can't the fatty acid with conjugated double bonds fit into the active site of enoyl-CoA hydratase?
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What is the consequence of the irreversibility of the condensation reaction of acetyl-CoA and oxaloacetate?
What is the consequence of the irreversibility of the condensation reaction of acetyl-CoA and oxaloacetate?
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What initial reaction occurs during the $β$-oxidation of saturated fatty acids?
What initial reaction occurs during the $β$-oxidation of saturated fatty acids?
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What is a main function of the citrate shuttle during fatty acid synthesis?
What is a main function of the citrate shuttle during fatty acid synthesis?
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What occurs when glucose is abundant in relation to acetyl-CoA?
What occurs when glucose is abundant in relation to acetyl-CoA?
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What is the primary purpose of the reciprocal regulation of fatty acid synthesis and oxidation?
What is the primary purpose of the reciprocal regulation of fatty acid synthesis and oxidation?
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Where does fatty acid synthesis occur within the cell?
Where does fatty acid synthesis occur within the cell?
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What is the effect of insulin on acetyl-CoA carboxylase (ACC) under high-glucose conditions?
What is the effect of insulin on acetyl-CoA carboxylase (ACC) under high-glucose conditions?
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How does malonyl-CoA contribute to the regulation of fatty acid metabolism?
How does malonyl-CoA contribute to the regulation of fatty acid metabolism?
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What triggers the release of glucagon in the body?
What triggers the release of glucagon in the body?
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What is the role of AMP-activated protein kinase (AMPK) in fatty acid metabolism?
What is the role of AMP-activated protein kinase (AMPK) in fatty acid metabolism?
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What condition favors fatty acid synthesis over $β$-oxidation?
What condition favors fatty acid synthesis over $β$-oxidation?
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Which factor must acetyl-CoA use to cross the inner mitochondrial membrane?
Which factor must acetyl-CoA use to cross the inner mitochondrial membrane?
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Study Notes
Fatty Acid Metabolism
- Lipids store significant energy, and their catabolism provides energy for many cellular functions, including gluconeogenesis in the liver
- Lipids are hydrophobic and require transport proteins or phospholipids for transport in the bloodstream
- Lipoproteins are amphiphilic molecules that carry lipids
- Lipoproteins have a core of triacylglycerol (triglyceride) and cholesterol esters and a phospholipid monolayer surrounding the core
- Dietary lipids are emulsified by bile salts to facilitate hydrolysis and absorption by intestinal cells
- Hydrolyzed lipids are converted into triacylglycerols in intestinal cells, packaged into chylomicrons, and transported to tissues
- Triglycerides in the liver are packaged into VLDLs, which transport triglycerides to other tissues
- Chylomicrons and VLDLs become chylomicron remnants and IDL, respectively, which are enriched in cholesterol and cholesteryl esters
- IDL can further be metabolized into LDL, delivering cholesterol to peripheral tissues
- HDLs may sequester cholesterol from peripheral tissues and transport it back to the liver
- Triglycerides are further hydrolyzed to free fatty acids and glycerol via lipase enzymes
- Free fatty acids are then used for energy via β-oxidation in mitochondria or peroxisomes
Fatty Acid Oxidation
- Fatty acids must enter the mitochondrial matrix, either directly (short-chain and some medium-chain) or via the carnitine shuttle (long-chain)
- Acyl-CoA is formed to facilitate entry into the matrix
- The process of beta-oxidation cycles through a series of steps, sequentially removing 2 carbon units from the fatty acid chain as acetyl-CoA molecules
- This cycle involves oxidation, hydration, oxidation, and deacetylation
- Oxidation generates FADH2 and NADH, which are important electron carriers in the electron transport chain
- Acetyl-CoA enters the citric acid cycle for further energy production
Unsaturated Fatty Acids
- Unsaturated fatty acids have one or more double bonds
- If the double bond is between odd and even numbers, β-oxidation proceeds normally until it reaches the double bond
- If the double bond is between two even numbered carbon atoms, enoyl-CoA isomerase converts the cis double bond to a trans double bond before β-oxidation proceeds
- 2,4-dienoyl-CoA reductase removes conjugated double bonds, placing a single double bond before proceeding with β-oxidation
Odd-Chain Fatty Acids
- Odd-chain fatty acids produce propionyl-CoA during the last round of β-oxidation
- Propionyl-CoA is carboxylated to D-methylmalonyl-CoA, then converted to L-methylmalonyl-CoA, later to succinyl-CoA
- This succinyl-CoA can enter the citric acid cycle
Ketone Bodies
- When excess acetyl-CoA is produced, it can be converted to ketone bodies (acetoacetate, D-β-hydroxybutyrate, and acetone) in the liver
- Ketone bodies are exported to other tissues, including the heart and muscles, for energy production
- Ketone bodies can be converted back to acetyl-CoA in other tissues for use in the citric acid cycle
Fatty Acid Synthesis
- Fatty acid synthesis occurs in the cytosol when glucose is abundant
- Acetyl-CoA must be transported out of the mitochondria by the citrate shuttle
- Acetyl-CoA is converted to malonyl-CoA via acetyl CoA carboxylase, which is the rate-limiting step in fatty acid synthesis
- Malonyl-CoA reacts with acetyl-CoA to form a four-carbon molecule, which is elongated and reduced in a repeated series of four reaction steps to yield a 16-carbon saturated fatty acid (palmitate)
- The process consumes malonyl-CoA and NADPH
- Excess glucose or insulin stimulates fatty acid synthesis, while glucagon or fasting inhibits the process
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Description
Test your knowledge on fatty acid metabolism and its related processes with this quiz. Explore topics such as triglyceride metabolism, the role of lipoproteins, and the steps involved in mitochondrial fatty acid oxidation. Ideal for students studying biochemistry or nutrition.
