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Questions and Answers
What is the primary site of β-oxidation in cells?
What is the primary site of β-oxidation in cells?
Which enzyme is responsible for the activation of fatty acids to form acyl CoA?
Which enzyme is responsible for the activation of fatty acids to form acyl CoA?
What effect does starvation have on fatty acid oxidation?
What effect does starvation have on fatty acid oxidation?
What is the primary function of the carnitine shuttle in β-oxidation?
What is the primary function of the carnitine shuttle in β-oxidation?
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Which of the following conditions inhibits β-oxidation?
Which of the following conditions inhibits β-oxidation?
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What is the total net energy produced from the beta-oxidation of palmitic acid?
What is the total net energy produced from the beta-oxidation of palmitic acid?
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How many acetyl-CoA molecules are produced from one complete beta-oxidation of palmitic acid?
How many acetyl-CoA molecules are produced from one complete beta-oxidation of palmitic acid?
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During the beta-oxidation of palmitic acid, which of the following is the energy yield from one molecule of acetyl-CoA in the Kreb's cycle?
During the beta-oxidation of palmitic acid, which of the following is the energy yield from one molecule of acetyl-CoA in the Kreb's cycle?
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What is the byproduct of fat oxidation when odd-chain fatty acids are metabolized?
What is the byproduct of fat oxidation when odd-chain fatty acids are metabolized?
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What type of oxidation occurs in tissues like the brain and liver and removes one carbon at a time from fatty acids?
What type of oxidation occurs in tissues like the brain and liver and removes one carbon at a time from fatty acids?
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Which process occurs when there is an excess of acetyl-CoA in the liver?
Which process occurs when there is an excess of acetyl-CoA in the liver?
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What is the metabolic fate of phytanic acid due to its methyl group at the beta position?
What is the metabolic fate of phytanic acid due to its methyl group at the beta position?
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Which of the following ketone bodies serves as an important fuel during fasting and starvation?
Which of the following ketone bodies serves as an important fuel during fasting and starvation?
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What process does the liver primarily use to synthesize ketone bodies?
What process does the liver primarily use to synthesize ketone bodies?
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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 is a direct consequence of increased lipolysis in adipose tissue on ketone body formation?
What is a direct consequence of increased lipolysis in adipose tissue on ketone body formation?
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Which enzyme's activity is crucial for regulating the entry of long-chain acyl CoA into mitochondria?
Which enzyme's activity is crucial for regulating the entry of long-chain acyl CoA into mitochondria?
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In what state does malonyl CoA inhibit ketogenesis?
In what state does malonyl CoA inhibit ketogenesis?
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Which ketone body is formed from acetoacetic acid through spontaneous decarboxylation?
Which ketone body is formed from acetoacetic acid through spontaneous decarboxylation?
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What is the consequence of decreased malonyl CoA during starvation?
What is the consequence of decreased malonyl CoA during starvation?
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The concentration of ketone bodies in the blood is generally limited to what maximum level?
The concentration of ketone bodies in the blood is generally limited to what maximum level?
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Study Notes
Fatty Acid Oxidation
- Fatty acid oxidation produces the most energy compared to other food sources. One gram of fat yields approximately 9 Kcal.
- Fatty acids come from the diet or through lipolysis in adipose tissue.
- Types of fatty acid oxidation include beta (β) oxidation (most common), alpha (α) oxidation, and omega (ω) oxidation.
Beta-Oxidation
- Site: Occurs within the mitochondria of liver, kidney, and heart cells.
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Steps:
- Activation: Fatty acids are activated in the cytoplasm by acyl-CoA synthetase (or thiokinase), requiring ATP.
- Transport: Activated fatty acids (acyl-CoA) are transported into the mitochondria via the carnitine shuttle. This involves 3 enzymes: carnitine acyltransferase I (in outer mitochondrial membrane), carnitine acylcarnitine translocase (in inner mitochondrial membrane), and carnitine acyltransferase II (in inner mitochondrial membrane). The inner mitochondrial membrane is impermeable to acyl-CoA, needing the shuttle.
- Oxidation Cycle: The acyl-CoA enters a cycle of reactions in the mitochondrial matrix, repeatedly removing two-carbon acetyl-CoA fragments. This cycle generates FADH2, NADH+H+, and (n-2) acyl-CoA.
Oxidation
- Location: Mitochondrial matrix
- Process: The cycle repeats until a two-carbon acetyl-CoA fragment remains. Each cycle produces FADH2, NADH+H+, and (n-2) acyl-CoA.
Energy Production from Palmitic Acid β-Oxidation
- Palmitic acid (a saturated fatty acid) oxidation repeats 7 cycles to yield 8 acetyl CoA.
- Each cycle generates:
- 1 FADH2
- 1 NADH+H+
- Each FADH2 yields 2 ATP during oxidative phosphorylation.
- Each NADH+H+ yields 3 ATP during oxidative phosphorylation.
- Acetyl CoA enters the citric acid cycle producing 12 ATP per molecule.
- Palmitic acid activation consumes 2 ATP.
- Overall, β-oxidation of palmitic acid yields a net of 129 ATP.
Odd-Numbered Fatty Acid Oxidation
- Odd-numbered fatty acids undergo beta-oxidation until a 3-carbon propionyl-CoA molecule remains.
- Propionyl-CoA goes into a specific biochemical pathway and contributes to glucose synthesis.
Alpha-Oxidation
- A minor pathway occurring in the brain and liver.
- Involves removing one carbon at a time from a carbon atom in a specific position (position α, hence the name).
- Does not produce significant energy.
Metabolism of Ketone Bodies
- High rates of fatty acid oxidation can generate more acetyl-CoA than the citric acid cycle can handle.
- Excess acetyl-CoA is converted into ketone bodies (acetoacetic acid, β-hydroxybutyric acid, and acetone).
- These ketone bodies can be used as an alternative fuel source by many tissues, particularly the brain, during prolonged fasting or starvation. The brain can utilize ketones as an energy source after a period of up to 5-10 days of starvation.
Importance of Ketone Bodies
- Provide energy to tissues other than the liver, especially during situations like prolonged fasting or starvation when glucose availability is limited.
- The brain can use ketone bodies as fuel after prolonged periods of starvation.
Ketone Body Synthesis (Ketogenesis)
- Definition: The process of synthesizing ketone bodies from acetyl-CoA.
- Location: Mitochondria of the liver cells.
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Steps:
- Formation of acetoacetyl-CoA. There are 2 pathways for this.
- Condensation of two acetyl-CoA molecules.
- Further processes produce acetoacetate, β-hydroxybutyrate, and acetone from acetoacetyl CoA.
Regulation of Ketogenesis
- Ketogenesis is stimulated by factors that increase fatty acid oxidation, such as:
- Increased lipolysis—leading to increased free fatty acid (FFA) in the blood.
- Increased activity of carnitine palmitoyltransferase I in the liver
- Lowered levels of insulin, (i.e., during fasting).
- The regulation of ketogenesis prevents uncontrolled accumulation of ketone bodies, especially during fasting or intense exercise where fatty acid oxidation is accelerated. The regulation ensures that only an acceptable level of ketone bodies is formed and circulated throughout the bodies.
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Description
Test your knowledge on fatty acid oxidation processes, including beta, alpha, and omega oxidation. Discover the energy yields and the mechanisms involved in fatty acid metabolism, particularly within mitochondrial cells. This quiz will challenge your understanding of crucial biochemical pathways.
