Beta-Oxidation and ATP Production
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Questions and Answers

What is the first step in the process of β-oxidation for fatty acyl-CoA?

  • Cleavage by β-ketoacyl-CoA thiolase
  • Oxidation to β-Ketoacyl-CoA
  • Formation of Enoyl-CoA (correct)
  • Hydration to 3-L-Hydroxyacyl-CoA

Which enzyme is responsible for the hydration step in β-oxidation?

  • β-ketoacyl-CoA thiolase
  • Enoyl-CoA hydratase (correct)
  • Acyl-CoA dehydrogenase
  • 3-L-hydroxyacyl-CoA dehydrogenase

During β-oxidation, what is produced when 3-L-hydroxyacyl-CoA is oxidized?

  • FADH2
  • Acetyl-CoA
  • NADH + H+ (correct)
  • Fatty acyl-CoA

How many ATP molecules are generated from one molecule of Palmitic Acid during complete β-oxidation?

<p>106 ATP (C)</p> Signup and view all the answers

What happens during the cleavage step of β-oxidation?

<p>Formation of Acetyl-CoA and a shorter fatty acyl-CoA (B)</p> Signup and view all the answers

Which of the following fatty acids produces more ATP through β-oxidation?

<p>Stearic Acid (C18:0) (D)</p> Signup and view all the answers

What is the role of CoA-SH in the β-oxidation pathway?

<p>Cleaves β-ketoacyl-CoA to form Acetyl-CoA (C)</p> Signup and view all the answers

What is a crucial requirement for the activation of fatty acids before β-oxidation can occur?

<p>ATP (A)</p> Signup and view all the answers

What is the primary function of Carnitine-Acyl Carnitine Translocase (CACT)?

<p>Facilitate the entry of acylcarnitine into mitochondria (C)</p> Signup and view all the answers

Which enzyme is responsible for converting LCFA-CoA to Acylcarnitine?

<p>Carnitine Palmitoyl Transferase - 1 (CPT-1) (C)</p> Signup and view all the answers

What happens to carnitine after acylcarnitine is converted back to LCFA-CoA?

<p>It is released into the cytosol (C)</p> Signup and view all the answers

Why can long-chain fatty acids (LCFAs) not cross the mitochondrial membrane in their CoA-activated form?

<p>They are incompatible with the lipid bilayer (B)</p> Signup and view all the answers

During what conditions does the carnitine shuttle notably help regulate fatty acid availability for energy?

<p>During periods of fasting (A)</p> Signup and view all the answers

Where is Carnitine Palmitoyl Transferase - 2 (CPT-2) located?

<p>Inner mitochondrial membrane (A)</p> Signup and view all the answers

What is the significance of the carnitine shuttle in fatty acid metabolism?

<p>It allows fatty acids to undergo β-oxidation for energy (A)</p> Signup and view all the answers

What is initially required to synthesize carnitine?

<p>Nε-trimethyllysine (TML) (B)</p> Signup and view all the answers

What is the role of 3-ketoacyl-CoA transferase in the ketolysis process?

<p>It converts acetoacetate to acetoacetyl-CoA. (D)</p> Signup and view all the answers

Why can't the liver perform ketolysis?

<p>It lacks the necessary enzyme for the process. (B)</p> Signup and view all the answers

Which hormone is primarily responsible for activating hormone-sensitive lipase during low fuel states?

<p>Glucagon (A)</p> Signup and view all the answers

What process is primarily stimulated by glucagon and epinephrine in the liver?

<p>Gluconeogenesis (A)</p> Signup and view all the answers

What is a result of the breakdown of fatty acids during energy mobilization?

<p>Production of ketone bodies (D)</p> Signup and view all the answers

What is the primary output of odd-chain fatty acid catabolism?

<p>Propionyl-CoA (D)</p> Signup and view all the answers

What is the main energy source mobilized by the body when fuel levels are low?

<p>Fatty acids (D)</p> Signup and view all the answers

Which enzyme is required for the conversion of propionyl-CoA to (S)-methylmalonyl-CoA?

<p>Propionyl-CoA Carboxylase (B)</p> Signup and view all the answers

What is necessary for the enzymatic reaction involving Methylmalonyl-CoA Mutase?

<p>Vitamin B12 (D)</p> Signup and view all the answers

Which enzyme is responsible for catalyzing the splitting of Acetoacetyl-CoA into two Acetyl-CoA molecules?

<p>Thiolase (A)</p> Signup and view all the answers

What is the consequence of the liver's inability to perform ketolysis?

<p>It primarily engages in ketogenesis. (A)</p> Signup and view all the answers

Which molecule is produced after the conversion of succinyl-CoA that integrates into the TCA cycle?

<p>Malate (D)</p> Signup and view all the answers

During ketogenesis, which organ primarily produces ketone bodies?

<p>Liver (A)</p> Signup and view all the answers

In the conversion sequence of propionyl-CoA to succinyl-CoA, which step does NOT directly consume ATP?

<p>Conversion of (S)-methylmalonyl-CoA to (R)-methylmalonyl-CoA (A)</p> Signup and view all the answers

What substance is released during the conversion of malate to pyruvate?

<p>CO2 (C)</p> Signup and view all the answers

Which of the following is NOT a product in the pathway leading from propionyl-CoA to succinyl-CoA?

<p>Acetyl-CoA (D)</p> Signup and view all the answers

What is the primary function of Acyl-CoA in fatty acid metabolism?

<p>To activate fatty acids for β-oxidation (A)</p> Signup and view all the answers

Which step in the formation of Acyl-CoA involves the hydrolysis of pyrophosphate?

<p>Hydrolysis of inorganic pyrophosphate (PPi) (A)</p> Signup and view all the answers

What is produced as a byproduct during the formation of Acyl-CoA?

<p>AMP (C)</p> Signup and view all the answers

Which enzyme is responsible for the conversion of Carnitine and LCFA-CoA to Acylcarnitine?

<p>Carnitine palmitoyl transferase - 1 (CPT-1) (D)</p> Signup and view all the answers

What is the role of ATP in the formation of Acyl-CoA?

<p>To activate the fatty acid (C)</p> Signup and view all the answers

Why is the hydrolysis of PPi crucial in the reaction pathway of Acyl-CoA formation?

<p>It prevents reverse reactions from occurring (A)</p> Signup and view all the answers

Which of the following lipids can Acyl-CoA directly contribute to the synthesis of?

<p>Phospholipids (C)</p> Signup and view all the answers

What is the main purpose of the carnitine shuttle mechanism?

<p>To transport long-chain fatty acids into mitochondria (B)</p> Signup and view all the answers

What is the primary problem encountered during the catabolism of unsaturated fatty acids like linoleic acid?

<p>Presence of double bonds (B)</p> Signup and view all the answers

Which enzyme is crucial for the isomerization step in the beta-oxidation of unsaturated fatty acids?

<p>3,2-enoyl-CoA isomerase (B)</p> Signup and view all the answers

What distinguishes the beta-oxidation of very long-chain fatty acids in peroxisomes from that in mitochondria?

<p>Direct transport system into peroxisome (A)</p> Signup and view all the answers

What is the role of catalase in the peroxisomal β-oxidation process?

<p>Decompose hydrogen peroxide into water and oxygen (D)</p> Signup and view all the answers

Which component is NOT generated during the beta-oxidation of linoleic acid?

<p>Carbon dioxide (CO2) (C)</p> Signup and view all the answers

What is the function of acyl-CoA dehydrogenase in the oxidation of VLCFAs in peroxisomes?

<p>Converting acyl-CoA to trans-enoyl-CoA (D)</p> Signup and view all the answers

Which situation indicates a problem during the beta-oxidation of unsaturated fatty acids?

<p>Formation of a 4,5-double bond (A)</p> Signup and view all the answers

In addition to beta-oxidation, what is another function of peroxisomes?

<p>Synthesis of bile acids (A)</p> Signup and view all the answers

Flashcards

β-Oxidation

Metabolic process that breaks down fatty acids into acetyl-CoA, providing energy, especially during fasting or low carbohydrate intake.

Fatty Acid Activation

The initial step in β-oxidation where fatty acids are activated by attaching them to coenzyme A, requiring ATP.

Carnitine Shuttle

Special transport system that moves activated long-chain fatty acids into the mitochondria for β-oxidation.

Formation of Enoyl-CoA

First step in β-oxidation: acyl-CoA dehydrogenase converts fatty acyl-CoA to trans-Δ²-enoyl-CoA, using FAD and producing FADH2.

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Hydration to 3-L-Hydroxyacyl-CoA

Second step in β-oxidation: enoyl-CoA hydratase adds water to trans-Δ²-enoyl-CoA to create 3-L-hydroxyacyl-CoA.

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Oxidation to β-Ketoacyl-CoA

Third step in β-oxidation: 3-L-hydroxyacyl-CoA dehydrogenase oxidizes 3-L-hydroxyacyl-CoA to β-ketoacyl-CoA, generating NADH.

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Cleavage to Acetyl-CoA

Final step in β-oxidation: β-ketoacyl-CoA thiolase cleaves β-ketoacyl-CoA using CoA-SH, producing acetyl-CoA and a shorter fatty acyl-CoA.

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Energy Yield from β-Oxidation of Palmitic Acid

Complete β-oxidation of a palmitic acid (C16:0) yields 8 acetyl-CoA, 7 FADH2, and 7 NADH, resulting in approximately 106 ATP molecules.

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What is Acyl-CoA formation?

An energy-requiring process that creates Acyl-CoA, a crucial molecule for fatty acid metabolism, from a fatty acid.

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What is acyladenylate?

A mixed anhydride formed during Acyl-CoA formation, where a fatty acid is linked to adenosine monophosphate (AMP).

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What is CPT-1 (Carnitine Palmitoyl Transferase - 1)?

An enzyme present on the inner mitochondrial membrane that catalyzes the conversion of Acyl-CoA into Acylcarnitine.

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What is Acylcarnitine?

A compound formed in the first step of the carnitine shuttle, allowing the transport of activated fatty acids into the mitochondria.

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What is the carnitine shuttle?

The process by which long-chain fatty acids (LCFAs) are transported into the mitochondria for β-oxidation.

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What is β-oxidation?

A process that breaks down fatty acids into acetyl-CoA, generating energy for the cell.

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What is the role of Acyl-CoA in fatty acid metabolism?

A vital molecule in fatty acid metabolism. It's the activated form of fatty acid that can enter the β-oxidation pathway.

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Why is Acyl-CoA formation an energetically expensive process?

The hydrolysis of ATP is needed to drive this reaction forward, indicating that this process consumes energy.

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What is the role of CACT in the carnitine shuttle?

Acylcarnitine is transported into the mitochondria via an antiporter called CACT, which also moves carnitine out of the mitochondria and into the cytosol.

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How does LCFA-CoA get ready to enter the mitochondria?

LCFA-CoA is converted to Acylcarnitine by CPT-1 on the outer mitochondrial membrane, allowing it to enter the mitochondria.

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What happens to Acylcarnitine inside the mitochondria?

Inside the mitochondria, Acylcarnitine is converted back to LCFA-CoA by CPT-2, which is found on the inner mitochondrial membrane. This process releases carnitine, which is then transported back to the cytosol by CACT.

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What is the main function of the carnitine shuttle?

Carnitine shuttles long-chain fatty acids (LCFAs) into the mitochondria where they can be broken down for energy production.

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Why is the carnitine shuttle necessary?

LCFAs cannot directly cross the mitochondrial membrane, but they can be transported by carnitine.

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How does the carnitine shuttle regulate metabolism?

It ensures the availability of fatty acids for energy production, particularly during periods of fasting or increased energy demands.

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What are the main enzymes involved in the carnitine shuttle?

The carnitine shuttle involves three key enzymes: CPT-1, CACT, and CPT-2.

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What is the importance of carnitine in fatty acid metabolism?

Carnitine is essential for the transport of fatty acids into the mitochondria, which is crucial for energy production.

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Ketolysis

The process of breaking down ketone bodies for energy.

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3-ketoacyl-CoA transferase

An enzyme critical for converting acetoacetate to acetoacetyl-CoA, a key step in ketolysis.

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Succinyl-CoA

A type of coenzyme that plays a role in various metabolic reactions, including ketolysis.

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Why the Liver Cannot Perform Ketolysis

The liver cannot break down ketone bodies for energy because it lacks the enzyme 3-ketoacyl-CoA transferase.

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Glucagon and Epinephrine

Hormones that trigger the breakdown of stored energy during times of low fuel availability.

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Hormone-sensitive Lipase

An enzyme activated by glucagon and epinephrine, which breaks down triglycerides into free fatty acids.

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Proteolysis

The breakdown of proteins into amino acids, stimulated by glucagon and epinephrine.

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Gluconeogenesis

The process of generating glucose from non-carbohydrate sources, activated by glucagon and epinephrine.

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Peroxisomal β-Oxidation

The process of breaking down fatty acids in peroxisomes.

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Propionyl-CoA

A 3-carbon molecule produced during the catabolism of odd-chain fatty acids.

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Propionyl-CoA Carboxylase

An enzyme involved in the conversion of propionyl-CoA to succinyl-CoA, requiring ATP and CO2.

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Methylmalonyl-CoA Racemase

An enzyme that converts (S)-methylmalonyl-CoA to (R)-methylmalonyl-CoA.

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Methylmalonyl-CoA Mutase

An enzyme that converts (R)-methylmalonyl-CoA to succinyl-CoA, requiring vitamin B12.

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Conversion of Propionyl-CoA to Succinyl-CoA

The process of converting propionyl-CoA to succinyl-CoA, involving carboxylation, racemization, and isomerization.

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Ketogenesis

The process by which the liver produces ketone bodies as an alternative fuel source during periods of limited glucose availability.

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Ketone Bodies as Fuel

Ketone bodies are used by tissues as fuel, especially during prolonged fasting or intense exercise.

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Unsaturated Fatty Acid Catabolism

The degradation of fatty acids with a double bond (unsaturated).

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Problem 1 (Unsaturated β-Oxidation)

A problem encountered in the catabolism of unsaturated fatty acids, caused by the presence of the double bond.

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Problem 2 (Unsaturated β-Oxidation)

A problem encountered in the catabolism of unsaturated fatty acids, where the double bond shifts to form a 4,5-double bond.

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Problem 3 (Unsaturated β-Oxidation)

The catabolic process of unsaturated fatty acids requires the presence of a double bond in the correct position (cis-3,4), needing an enzyme to shift/isomerize it. This problem, known as Problem 3, requires further isomerization for β-oxidation to continue.

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Peroxisomes

Specialized organelles in cells responsible for the metabolism of very long-chain fatty acids (VLCFAs).

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Very Long-Chain Fatty Acids (VLCFAs)

Fatty acids containing more than 20 carbon atoms.

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Peroxisome-Specific Acyl-CoA Dehydrogenase

The β-oxidation pathway in peroxisomes is analogous to the one in mitochondria, but with a different first enzyme and a different reaction sequence. This enzyme is involved in the initial oxidation of the acyl-CoA molecule.

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Catalase

An enzyme found in peroxisomes that decomposes hydrogen peroxide (H2O2), a byproduct of fatty acid oxidation, into water (H2O) and oxygen (1/2 O2).

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Study Notes

Beta-Oxidation and ATP Production

  • Beta-oxidation is a metabolic process breaking down fatty acids to create acetyl-CoA, which enters the citric acid cycle (TCA cycle) to produce ATP.
  • Crucial for energy production during fasting or low carbohydrate intake.
  • Fatty acids are first activated by linking them to coenzyme A (CoA), requiring ATP.
  • Activated fatty acyl-CoA is transported to the mitochondria, mainly via the carnitine shuttle.

Enzymatic Steps of Beta-Oxidation

  • Four repeating enzymatic steps oxidize fatty acyl-CoA completely.
  • Formation of Enoyl-CoA: Fatty acyl-CoA converts to trans-Δ2-enoyl-CoA by acyl-CoA dehydrogenase, using FAD and forming FADH2.
  • Hydration to 3-L-Hydroxyacyl-CoA: Trans-Δ2-enoyl-CoA hydrates to form 3-L-hydroxyacyl-CoA using enoyl-CoA hydratase.
  • Oxidation to β-Ketoacyl-CoA: 3-L-hydroxyacyl-CoA is oxidized to β-ketoacyl-CoA by 3-L-hydroxyacyl-CoA dehydrogenase, consuming NAD+ and producing NADH+H+.
  • Cleavage to Acetyl-CoA: β-ketoacyl-CoA is cleaved by β-ketoacyl-CoA thiolase, using CoA-SH, yielding acetyl-CoA and a shorter fatty acyl-CoA chain.

Energy Yield from β-Oxidation

  • Complete β-oxidation yields significant ATP.
  • Palmitic Acid (C16:0): Produces 8 acetyl-CoA, 7 FADH2, and 7 NADH, yielding a total of 106 ATP.
  • Stearic Acid (C18:0): Produces 9 acetyl-CoA, 8 FADH2, and 8 NADH, yielding a total of 120 ATP.

Fatty Acid Absorption and Transport

  • Short-chain fatty acids (SCFAs) and medium-chain fatty acids (MCFAs) diffuse across the plasma membrane.
  • Long-chain fatty acids (LCFAs) require transporters (e.g., FA translocase, FATP5) for transport.
  • Dietary fats form micelles aiding intestinal absorption. SCFAs/MCFAs enter the portal circulation, LCFAs are packaged into chylomicrons and enter the lymphatic system then bloodstream.

Formation of Acyl-CoA

  • Acyl-CoA synthetase activates fatty acids.
  • Reaction summary: Fatty acid + ATP → Acyl-Adenylate (intermediate) + AMP + PPi; Acyl-Adenylate + CoA → Acyl-CoA + AMP.
  • Hydrolysis of inorganic pyrophosphate (PPi) drives the reaction forward.

Carnitine Shuttle Mechanism

  • Carnitine shuttle transports long-chain fatty acids (LCFAs) into mitochondria for β-oxidation.
  • CPT-1 (Carnitine palmitoyl transferase 1) converts LCFA-CoA to Acylcarnitine.
  • Acylcarnitine crosses the inner mitochondrial membrane via CACT (Carnitine-acylcarnitine translocase).
  • CPT-2 converts Acylcarnitine back to LCFA-CoA inside the mitochondria.

Importance of Carnitine in Fatty Acid Metabolism

  • Crucial for energy production.
  • Acyl-CoA is the activated form for β-oxidation.
  • Fatty acids are utilized for energy, particularly in fasting or low carbohydrate intake periods.
  • Critical in both the catabolism and anabolism of fatty acids.

Odd-Chain Fatty Acid Catabolism

  • Odd-chain fatty acid catabolism produces propionyl-CoA (3-carbon molecule), a crucial step in integrating odd-chain fatty acid metabolism into the TCA cycle.
  • Propionyl-CoA converts to Succinyl-CoA via three enzymatic steps; propionyl-CoA carboxylase, methylmalonyl-CoA racemase, and methylmalonyl-CoA mutase.

Ketogenesis in the Liver

  • Ketogenesis is a metabolic process converting acetyl-CoA from β-oxidation into ketone bodies.
  • Important for tissues during low carbohydrate availability or fasting
  • Key ketone bodies: acetone, acetoacetate, and β-hydroxybutyrate

Steps of Ketogenesis

  • Formation of Acetoacetyl-CoA from two molecules of acetyl-CoA.
  • Conversion of Acetoacetyl-CoA to HMG-CoA.
  • Formation of Acetoacetate from HMG-CoA.
  • Conversion of Acetoacetate to acetone or β-hydroxybutyrate.

Ketolysis in Peripheral Tissues

  • Peripheral tissues (e.g., brain, heart, muscles) utilize ketone bodies for energy during prolonged fasting/ketosis.
  • Ketolysis converts ketone bodies to acetyl-CoA for ATP production.
  • Key enzymes: β-hydroxybutyrate dehydrogenase, 3-ketoacyl-CoA transferase, and thiolase.

Hormonal regulation of β-oxidation

  • Glucagon and epinephrine regulate β-oxidation.
  • Hormonal activation of hormone-sensitive lipase in adipose tissues to release fatty acids.
  • Hormonal activation of proteolyses in muscle to provide amino acids as energy source/gluconeogenesis.
  • Insulin reverses the effects of glucagon and epinephrine by promoting energy storage.

Peroxisomal β-Oxidation

  • Peroxisomes are involved in the β oxidation of very long-chain fatty acids (VLCFAs).
  • This process involves the enzymes acyl-CoA dehydrogenase, which catalyzes the initial oxidation of the acyl-CoA molecule.
  • Other processes involve hydration, further oxidation, and thiolysis of VLCFA-CoA for production of shorter chain acyl-CoA molecules.
  • Important: The presence of catalase in peroxisomes is crucial for decomposing hydrogen peroxide (Hâ‚‚Oâ‚‚) generated as a byproduct of fatty acid oxidation, preventing harm to the cell.

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Description

This quiz explores the processes of beta-oxidation and ATP production from fatty acids. It covers the steps involved in converting fatty acyl-CoA to acetyl-CoA and the importance of this process during fasting or low carbohydrate intake. Test your knowledge of the enzymatic steps and their roles in energy metabolism.

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