The citric acid cycle is a crucial metabolic pathway that breaks down nutrients for energy. It involves a series of enzyme-catalyzed reactions, producing high-energy molecules like NADH and FADH2 that fuel production.
Regulation of the cycle is key to maintaining energy balance. Allosteric enzymes respond to cellular energy levels, adjusting cycle activity based on ATP, NADH, and substrate availability. This fine-tuning ensures efficient energy production.
Citric Acid Cycle Enzymes
Catalytic Roles and Reactions
Top images from around the web for Catalytic Roles and Reactions
Oxidation of Pyruvate and the Citric Acid Cycle · Biology View original
Is this image relevant?
1 of 3
catalyzes the condensation of and to form , marking the first step of the citric acid cycle
isomerizes citrate to via the intermediate cis-aconitate, allowing for the continuation of the cycle
oxidatively decarboxylates isocitrate to form α-ketoglutarate, generating NADH in the process and contributing to the cycle's energy production
α-Ketoglutarate dehydrogenase catalyzes the oxidative decarboxylation of α-ketoglutarate to form , generating NADH and serving as a key regulatory point in the cycle
catalyzes the substrate-level phosphorylation of GDP or ADP to form or ATP, respectively, while converting succinyl- to
Oxidation-Reduction Reactions and Electron Transport
oxidizes succinate to , reducing to FADH2 and serving as a direct link between the citric acid cycle and the
catalyzes the hydration of fumarate to form , preparing the substrate for the final step of the cycle
oxidizes malate to oxaloacetate, regenerating the starting compound of the citric acid cycle and reducing to NADH, which can feed into the electron transport chain
Energy Molecules and Regulation
High-Energy Compounds and Electron Carriers
Acetyl-CoA, a high-energy compound derived from the oxidation of carbohydrates, fats, and proteins, serves as the primary input for the citric acid cycle
NADH, produced by several enzymes in the citric acid cycle (isocitrate dehydrogenase, α-ketoglutarate dehydrogenase, and malate dehydrogenase), transfers electrons to the electron transport chain for ATP production
FADH2, generated by succinate dehydrogenase, also transfers electrons to the electron transport chain, contributing to the proton gradient and subsequent ATP synthesis
ATP, the primary energy currency of the cell, is directly produced by succinyl-CoA synthetase through substrate-level phosphorylation and indirectly via the electron transport chain and
Allosteric Regulation and Metabolic Control
of citric acid cycle enzymes allows for precise control of the cycle's activity in response to the cell's energy demands and substrate availability
Citrate synthase is inhibited by high levels of ATP, acetyl-CoA, and NADH, ensuring that the cycle does not proceed when energy is abundant or when there is a build-up of intermediates
Isocitrate dehydrogenase is allosterically stimulated by ADP and inhibited by ATP and NADH, fine-tuning the cycle's activity based on the cell's energy status
α-Ketoglutarate dehydrogenase is inhibited by high levels of NADH and succinyl-CoA, preventing the excessive accumulation of these compounds and maintaining the cycle's balance
The citric acid cycle's regulation is closely linked to that of glycolysis and the electron transport chain, allowing for the coordinated control of cellular energy production in response to varying conditions (glucose availability, oxygen levels)