Questions and Answers
What are cataplerotic reactions?
A series of reactions that deplete CAC intermediates.
What are sterols?
They are cholesterol-based substances like cortisol, testosterone, and estrogen.
What are the cataplerotic reactions?
- Phosphoenolpyruvate carboxykinase, 2. Aspartate transaminase, 3. ATP citrate lyase, 4. Glutamate dehydrogenase, 5. Aminolevulinate synthase.
What are the situations in which the cataplerotic reactions will be active?
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What are anaplerotic reactions?
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What are the anaplerotic reactions?
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What does phosphoenolpyruvate carboxykinase do?
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What is the reaction that phosphoenolpyruvate carboxykinase catalyzes?
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What does ATP citrate lyase do?
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What is the reaction that ATP citrate lyase catalyzes?
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Is ATP citrate lyase cataplerotic or anaplerotic?
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What does Delta-aminolevulinate synthase do?
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How is the Delta-aminolevulinate synthase the first step in heme formation?
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What does each of the catapleronic reactions go to?
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What does adenylosuccinate lyase do?
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What is the reaction for the breakdown of adenylosuccinate?
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What is the breakdown of SAICAR?
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What does malic enzyme do?
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What is malic enzyme's full name?
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What is malate dehydrogenase similar to?
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What changes the malate dehydrogenase varieties?
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What does pyruvate carboxylase do?
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What is the pyruvate carboxylase reaction?
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How is the pyruvate carboxylase regulated?
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What does beta oxidation do?
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What happens when the fatty acid has an odd number of carbons during beta oxidation?
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What does Aspartate Transaminase do?
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Is Aspartate transaminase anaplerotic or cataplerotic?
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What does glutamate dehydrogenase do?
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How is glutamate dehydrogenase similar to aspartate transaminase?
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What is the TCA?
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Study Notes
Cataplerotic Reactions
- Deplete citric acid cycle (CAC) intermediates, known as "emptying reactions."
- Intermediates are diverted for biosynthesis of important molecules.
- Active during DNA synthesis, RBC production, storage of energy as fatty acids, post-meal scenarios, and steroid signaling.
- Key cataplerotic reactions include:
- Phosphoenolpyruvate carboxykinase (converts oxaloacetate to phosphoenolpyruvate)
- Aspartate transaminase (transfers amino groups)
- ATP citrate lyase (breaks down citrate into oxaloacetate and acetyl CoA)
- Glutamate dehydrogenase (removes hydrogen from glutamate)
- Delta-aminolevulinate synthase (first step in heme formation)
Anaplerotic Reactions
- Build up CAC intermediates, balancing their depletion for biosynthesis.
- Promote the replenishment of intermediates used in various metabolic pathways.
- Key anaplerotic reactions include:
- Pyruvate carboxylase (adds carbon to pyruvate)
- Beta oxidation of fatty acids (releases acetyl CoA)
- Glutamate dehydrogenase (also acts in anaplerotic direction)
- Aspartate transaminase (can function in both directions)
- Adenylosuccinate lyase (involved in nucleotide synthesis)
Enzyme Functions and Roles
-
Phosphoenolpyruvate carboxykinase
- Catalyzes reaction: GTP + oxaloacetate → GDP + PEP + CO2.
- Converts oxaloacetate to phosphoenolpyruvate during gluconeogenesis.
-
ATP Citrate Lyase
- Breaks down citrate in the cytoplasm while consuming ATP.
- Reaction: citrate + ATP + CoA → oxaloacetate + ADP + Pi + acetyl CoA.
- Functions in fatty acid and sterol biosynthesis.
-
Delta-Aminolevulinate Synthase
- Key in heme formation, synthesizes delta-aminolevulinate (ALA) from precursor molecules.
-
Adenylosuccinate Lyase
- Catalyzes breakdown of adenylosuccinate into AMP and fumarate.
-
Malic Enzyme
- Converts pyruvate to L-malate while producing NADP+.
- Similar in function to pyruvate carboxylase.
Additional Key Concepts
-
Beta Oxidation
- Breaks down fatty acids, releasing acetyl CoA at each step.
- When fatty acids have odd carbon numbers, results in propionyl CoA, which is converted to succinyl CoA.
-
Aspartate Transaminase
- Catalyzes the reversible transfer of amino groups between aspartate and α-ketoglutarate.
- Functions in both cataplerotic and anaplerotic capacities, making it amphiplerotic.
-
Glutamate Dehydrogenase
- Removes hydrogen from glutamate, can utilize NAD or NADP.
- Also amphiplerotic, functioning depending on reaction direction.
-
TCA Cycle
- Functions as an amphiplerotic mechanism, balancing catabolic and anabolic processes in the body.
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Test your knowledge on cataplerotic and anaplerotic reactions with these flashcards. Explore definitions, key reactions, and understand the role of sterols in the metabolic pathways. Perfect for students of biochemistry and related fields.