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Questions and Answers
What is the primary site for β-oxidation of fatty acids in the body?
What is the primary site for β-oxidation of fatty acids in the body?
Which of the following directly activates fatty acids for oxidation?
Which of the following directly activates fatty acids for oxidation?
Which component is essential for the transport of acyl CoA into the mitochondria?
Which component is essential for the transport of acyl CoA into the mitochondria?
What effect does insulin have on fatty acid oxidation?
What effect does insulin have on fatty acid oxidation?
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Which enzyme is responsible for converting acyl CoA into its active form during β-oxidation?
Which enzyme is responsible for converting acyl CoA into its active form during β-oxidation?
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How many acetyl CoA molecules are produced from one complete cycle of β-oxidation of palmitic acid?
How many acetyl CoA molecules are produced from one complete cycle of β-oxidation of palmitic acid?
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What is the total net energy produced from the β-oxidation of palmitic acid?
What is the total net energy produced from the β-oxidation of palmitic acid?
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What happens to propionyl CoA after oxidation of odd-numbered fatty acids?
What happens to propionyl CoA after oxidation of odd-numbered fatty acids?
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Which fatty acid oxidation pathway occurs mainly in the brain?
Which fatty acid oxidation pathway occurs mainly in the brain?
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Which of the following is NOT a type of ketone body?
Which of the following is NOT a type of ketone body?
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What is the significance of ketone bodies during fasting?
What is the significance of ketone bodies during fasting?
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In the formula for calculating energy from even-numbered fatty acids, what does N represent?
In the formula for calculating energy from even-numbered fatty acids, what does N represent?
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What is the consumption of high energy bonds during the activation of fatty acids to acyl CoA?
What is the consumption of high energy bonds during the activation of fatty acids to acyl CoA?
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What is the primary site of ketone body synthesis?
What is the primary site of ketone body synthesis?
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Which pathway does NOT contribute to the formation of acetoacetyl CoA?
Which pathway does NOT contribute to the formation of acetoacetyl CoA?
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What happens to ketone body production during starvation?
What happens to ketone body production during starvation?
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What is the role of carnitine palmitoyl transferase-I in ketogenesis?
What is the role of carnitine palmitoyl transferase-I in ketogenesis?
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Which statement is true about the liver's utilization of ketone bodies?
Which statement is true about the liver's utilization of ketone bodies?
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What initiates the increased formation of ketone bodies?
What initiates the increased formation of ketone bodies?
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What product is formed directly from acetoacetyl CoA by deacylation?
What product is formed directly from acetoacetyl CoA by deacylation?
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How does malonyl CoA affect ketogenesis during the fed state?
How does malonyl CoA affect ketogenesis during the fed state?
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Study Notes
Fatty Acid Oxidation
- Fatty acid oxidation releases the maximum energy among food sources.
- One gram of fat produces approximately 9 Kcal of energy.
- Fatty acids are derived from the diet and lipolysis of adipose tissue.
- Types of fatty acid oxidation include beta (β) oxidation (most common), alpha (α) oxidation, and omega (ω) oxidation.
Beta-Oxidation
- Occurs in the mitochondria.
- Specific organ sites include liver, kidney, and heart.
- Involves three steps:
- Activation of fatty acids to acyl CoA: fatty acids are activated in the cytoplasm before entering the mitochondria by acyl-CoA synthetase or thiokinase. This process requires ATP.
- Transport of Acyl CoA into Mitochondria via the Carnitine Shuttle: The inner mitochondrial membrane is impermeable to acyl CoA. The carnitine shuttle facilitates transport using:
- Carnitine acyltransferase I (in outer mitochondrial membrane)
- Carnitine acylcarnitine translocase (in inner mitochondrial membrane)
- Carnitine acyltransferase II (in inner mitochondrial membrane).
- Oxidation in the Mitochondrial Matrix: A series of enzymatic reactions within the mitochondrial matrix break down acyl-CoA into acetyl-CoA, FADH2, and NADH.
Oxidation in the Mitochondrial Matrix
- Occurs in the mitochondrial matrix.
- A series of enzymatic reactions break down acyl-CoA into acetyl-CoA, FADH2, and NADH.
- The reactions proceed sequentially producing, FADH2, NADH, and acetyl CoA which enters the citric acid cycle.
Regulation of FA Oxidation
- Glucose oxidation is inversely related to fatty acid oxidation. In diabetes mellitus or starvation, where glucose is insufficient, fatty acid oxidation increases.
- Starvation and low blood glucose levels increase lipolysis, releasing fatty acids, and stimulating fatty acid oxidation.
- Insulin and carbohydrate intake inhibit fatty acid oxidation.
Energy Production from Beta-Oxidation
- Palmitic acid (16-carbon fatty acid) undergoes beta-oxidation 7 times.
- Each cycle produces one FADH2 and one NADH + H+.
- Acetyl-CoA enters the citric acid cycle producing ATP.
- 7 cycles produce 7FADH2 and 7NADH+H+ and 8 acetyl CoA.
- 7 cycles * 5ATP (from FADH2) + 7 cycles * 3ATP = 35 ATP
- 8 acetyl CoA * 12 ATP (from citric acid cycle) = 96 ATP
- Activation of palmitic acid to acyl-CoA uses 2 ATP
- Total energy yield from beta-oxidation of palmitic acid = 129 ATP
Odd Number Fatty Acid Oxidation
- Fatty acids with an odd number of carbons are oxidized similarly to even-numbered fatty acids until a 3-carbon residue (propionyl CoA) remains.
- Propionyl CoA is converted to succinyl CoA, entering the citric acid cycle for further energy production or glucose synthesis (gluconeogenesis).
Alpha (α) Oxidation
- A minor pathway.
- Occurs primarily in the brain and liver.
- Removes one carbon atom at a time, from a specific position.
- Does not require coenzyme A (CoA).
- Important for the metabolism of methylated fatty acids like phytanic acid (found in ruminant tissues and dairy products).
- The methyl group in phytanic acid blocks beta-oxidation, hence, it undergoes alpha-oxidation.
Metabolism of Ketone Bodies
- During high rates of fatty acid oxidation (particularly in the liver), the production of acetyl-CoA exceeds the capacity of the citric acid cycle.
- This excess acetyl-CoA is converted into ketone bodies (acetoacetic acid, beta-hydroxybutyric acid, and acetone).
- Ketone bodies are transported to other tissues (especially the brain) as alternative energy sources during prolonged fasting or starvation.
Importance of Ketone Bodies
- Critical energy source for tissues, particularly the brain.
- Utilizable in prolonged fasting or starvation when glucose is scarce.
- The brain can utilize ketone bodies after a few days (5 to 10) of starvation.
- The total blood concentration of ketone bodies does not exceed 2 mg/dl.
Ketone Body Synthesis (Ketogenesis)
- The synthesis process is called ketogenesis which occurs in the liver.
- Ketone bodies are made from acetyl CoA.
- Acetoacetyl CoA is a key intermediate formed by two pathways (condensation of two acetyl CoA molecules or during beta-oxidation.)
- Acetoacetate is generated by decarboxylation from acetoacetyl CoA.
- Acetoacetate can also be reduced to beta-hydroxybutyrate or decarboxylated to generate acetone
Regulation of Ketogenesis
- Lipolysis in adipose tissue is a primary driver of ketogenesis through increasing free fatty acid (FFA) delivery to the liver.
- Increased liver carnitine palmitoyltransferase-I (CPT-I) activity and serum free fatty acid levels.
- In the fed state, high insulin /glucagon levels inhibit CPT-I activity, thus reducing ketogenesis, where malonyl-CoA inhibits CPT-I.
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Description
Test your knowledge on fatty acid oxidation, focusing on β-oxidation processes, key enzymes, and metabolic pathways. This quiz covers topics such as the activation of fatty acids, the role of insulin, and the energy yield from palmitic acid oxidation. Challenge yourself with questions about key components and pathways involved in fatty acid metabolism.
