Questions and Answers
Where does the citric acid cycle take place?
mitochondrial matrix
What's the main purpose of the citric acid cycle?
To oxidize carbons in intermediates to CO2 and generate high-energy electron carriers (NADH and FADH2), and GTP.
_________ couples acetyl-CoA to oxaloacetate and then hydrolyzes the resulting product, forming ______ and CoA-SH.
Citrate synthase, citrate
________ isomerizes citrate to _________
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What enzyme oxidizes and decarboxylates isocitrate to form alpha-ketoglutarate?
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Is the oxidation and decarboxylation of isocitrate a rate-limiting step?
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What are the inhibitors and activators of isocitrate dehydrogenase?
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What does alpha-ketoglutarate dehydrogenase complex metabolize to form?
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Is alpha-ketoglutarate dehydrogenase complex activated by ATP?
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What does succinyl-CoA synthetase generate?
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___________ oxidizes succinate to form______.
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______ hydrolyzes the alkene bond for fumarate to form______.
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What does malate dehydrogenase oxidize malate to?
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Study Notes
Citric Acid Cycle Overview
- The citric acid cycle occurs in the mitochondrial matrix, a central metabolic pathway.
- Its main purpose is to oxidize carbon atoms in intermediates to carbon dioxide (CO2) and generate high-energy electron carriers such as NADH and FADH2, along with GTP.
Key Enzymes and Reactions
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Citrate Synthase: Couples acetyl-CoA to oxaloacetate, hydrolyzing the product to form citrate and CoA-SH. It is negatively regulated by ATP, NADH, succinyl-CoA, and citrate.
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Aconitase: Isomerizes citrate to isocitrate, facilitating the next steps in the cycle.
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Isocitrate Dehydrogenase: Catalyzes the oxidation and decarboxylation of isocitrate to produce alpha-ketoglutarate. This is a rate-limiting step, generating the first CO2 and NADH of the cycle. It is heavily regulated: inhibited by ATP and NADH, activated by ADP and NAD+.
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Alpha-Ketoglutarate Dehydrogenase Complex: Similar to the Pyruvate Dehydrogenase (PDH) complex, it metabolizes alpha-ketoglutarate to form succinyl-CoA, generating the second CO2 and NADH. Inhibition occurs via ATP, NADH, and succinyl-CoA, whereas activation is done by ADP and Ca2+.
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Succinyl-CoA Synthetase: Hydrolyzes the thioester bond in succinyl-CoA, yielding succinate and CoA-SH. This enzyme generates one GTP during the cycle.
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Succinate Dehydrogenase: Oxidizes succinate to fumarate and is a flavoprotein attached to the inner mitochondrial membrane. It requires FAD, which is reduced to produce the only FADH2 generated in the cycle.
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Fumarase: Hydrolyzes the alkene bond in fumarate to form malate.
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Malate Dehydrogenase: Oxidizes malate back to oxaloacetate, generating the third and final NADH of the citric acid cycle.
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Description
Test your knowledge on the reactions of the citric acid cycle with this quiz. Learn about the location, purpose, and key enzymes involved in this crucial metabolic pathway. Perfect for students studying biochemistry or related fields.
