Questions and Answers
Where does the Citric Acid Cycle occur?
The Citric Acid Cycle occurs in the mitochondria.
When does the oxidative decarboxylation of pyruvate occur?
It occurs after glycolysis in the mitochondrion, but before the Citric Acid Cycle.
What enzyme acts as a catalyst for the formation of acetyl-CoA?
The reaction is catalyzed by the pyruvate dehydrogenase complex.
Where is the Citric Acid Cycle generally considered to 'start'?
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Rearrangement of citrate to isocitrate is catalyzed by aconitase.
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Oxidative decarboxylation of alpha-ketoglutarate occurs in the fourth step.
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What is the fifth step of the Citric Acid Cycle?
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The remaining steps of the Citric Acid Cycle are devoted to regenerating oxaloacetate.
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What is the name of the only enzyme of the Citric Acid Cycle that isn't found in the mitochondrial matrix?
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What happens in the seventh reaction of the Citric Acid Cycle?
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What happens during the eighth step of the Citric Acid Cycle?
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Both alpha-ketoglutarate and oxaloacetate can be converted into amino acids.
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Study Notes
Citric Acid Cycle Overview
- Occurs in the mitochondria, specifically within the inner membrane and mitochondrial matrix.
- Involves crucial components: inner membrane, matrix where enzymes are dissolved, and cristae (infoldings of the inner membrane).
Oxidative Decarboxylation of Pyruvate
- Takes place in the mitochondrion after glycolysis and before the Citric Acid Cycle.
- Catalyzed by the pyruvate dehydrogenase complex to form acetyl-CoA.
- Characterized by large negative free energy (delta G) and formation of the activated acetate in the form of a thioester bond.
Starting Point of the Citric Acid Cycle
- Begins with the addition of acetyl-CoA to oxaloacetate (OAA), resulting in citrate.
- Utilizes the energy from the high-energy thioester bond in acetyl-CoA, with coenzyme A released during the reaction.
Key Steps and Enzymes
- Citrate Rearrangement: Aconitase catalyzes the conversion of citrate to isocitrate.
- Fourth Step: Alpha-ketoglutarate undergoes oxidative decarboxylation catalyzed by alpha-ketoglutarate dehydrogenase (alphaKGDH), resulting in succinyl-CoA.
- Fifth Step: Involves substrate-level phosphorylation, producing GTP and releasing coenzyme A, catalyzed by succinyl-CoA synthetase.
- Subsequent Steps: Devoted to regenerating oxaloacetate; includes oxidation of succinate to fumarate catalyzed by succinate dehydrogenase, which uses FAD instead of NAD.
Unique Properties of Enzymes
- Succinate dehydrogenase is unique as it is embedded in the inner mitochondrial membrane rather than located in the matrix.
Water Addition and Oxidation Reactions
- Seventh reaction: Water is added to fumarate to yield L-malate, catalyzed by fumarase.
- Eighth step: Involves oxidation of malate to oxaloacetate, producing NADH and requiring energy input, catalyzed by malate dehydrogenase.
Amino Acid Interconversion
- Both alpha-ketoglutarate and oxaloacetate can be converted into the amino acids glutamate and aspartate, respectively.
- Pyruvate can also be converted to alanine, highlighting the interconnectedness of metabolic pathways.
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Description
Test your knowledge on the Citric Acid Cycle with these flashcards. Learn about its location, key reactions, and important processes involved. Perfect for students looking to reinforce their understanding of cellular respiration.
