3 min read•Last Updated on August 16, 2024
The citric acid cycle, a key part of carbohydrate metabolism, breaks down acetyl-CoA to produce energy-rich molecules. This process, occurring in the mitochondria, involves eight enzymatic reactions that oxidize and decarboxylate substrates, generating NADH, FADH2, and GTP.
Regulation of the cycle is crucial for maintaining energy balance. Allosteric enzymes respond to energy levels, while substrate availability and hormonal signals fine-tune the process. The cycle also serves anabolic functions, providing precursors for various biosynthetic pathways.
Citric acid cycle - wikidoc View original
Is this image relevant?
Oxidation of Pyruvate and the Citric Acid Cycle | OpenStax Biology 2e View original
Is this image relevant?
5.6C: Acetyl CoA and the Citric Acid Cycle - Biology LibreTexts View original
Is this image relevant?
Citric acid cycle - wikidoc View original
Is this image relevant?
Oxidation of Pyruvate and the Citric Acid Cycle | OpenStax Biology 2e View original
Is this image relevant?
1 of 3
Citric acid cycle - wikidoc View original
Is this image relevant?
Oxidation of Pyruvate and the Citric Acid Cycle | OpenStax Biology 2e View original
Is this image relevant?
5.6C: Acetyl CoA and the Citric Acid Cycle - Biology LibreTexts View original
Is this image relevant?
Citric acid cycle - wikidoc View original
Is this image relevant?
Oxidation of Pyruvate and the Citric Acid Cycle | OpenStax Biology 2e View original
Is this image relevant?
1 of 3
Aconitase is an enzyme that plays a critical role in the citric acid cycle, catalyzing the isomerization of citrate to isocitrate through a two-step process. This enzyme is important for facilitating energy production in aerobic respiration and helps regulate the flow of metabolites within the cycle, impacting overall cellular metabolism.
Term 1 of 32
Aconitase is an enzyme that plays a critical role in the citric acid cycle, catalyzing the isomerization of citrate to isocitrate through a two-step process. This enzyme is important for facilitating energy production in aerobic respiration and helps regulate the flow of metabolites within the cycle, impacting overall cellular metabolism.
Term 1 of 32
NADH, or nicotinamide adenine dinucleotide (reduced form), is a crucial coenzyme in cellular metabolism that acts as an electron carrier in redox reactions. It plays a significant role in energy production by facilitating the transfer of electrons during metabolic pathways such as glycolysis and the citric acid cycle, ultimately contributing to ATP synthesis through oxidative phosphorylation.
Electron Transport Chain: A series of protein complexes located in the inner mitochondrial membrane that transfer electrons from NADH and FADH2 to oxygen, creating a proton gradient used for ATP synthesis.
Oxidative Phosphorylation: The metabolic pathway where ATP is produced using energy derived from the transfer of electrons through the electron transport chain, driven by the oxidation of NADH and FADH2.
Citric Acid Cycle: A series of enzymatic reactions occurring in the mitochondrial matrix that oxidizes acetyl-CoA to produce NADH, FADH2, and ATP, serving as key inputs for oxidative phosphorylation.
FADH2 is a reduced coenzyme derived from riboflavin that plays a crucial role in the metabolism of carbohydrates, fatty acids, and amino acids. It acts as an electron carrier in cellular respiration, specifically in the electron transport chain, contributing to the production of ATP through oxidative phosphorylation.
FAD: Flavin adenine dinucleotide, the oxidized form of FADH2 that accepts electrons during metabolic reactions.
Electron Transport Chain: A series of protein complexes and other molecules located in the inner mitochondrial membrane that transfer electrons from electron donors like FADH2 and NADH to electron acceptors, ultimately generating ATP.
ATP Synthase: An enzyme complex that utilizes the proton gradient established by the electron transport chain to synthesize ATP from ADP and inorganic phosphate.
Guanosine triphosphate (GTP) is a nucleotide that serves as a critical energy source and a signaling molecule in cellular processes. It plays a significant role in protein synthesis and cell signaling, particularly in the activation of G-proteins. GTP is involved in various metabolic pathways, making it integral to energy metabolism and cellular regulation.
ATP: Adenosine triphosphate (ATP) is the primary energy carrier in cells, providing energy for many biochemical reactions.
G-proteins: G-proteins are molecular switches that transmit signals from outside the cell to the inside, activated by the binding of GTP.
Nucleotide: Nucleotides are the building blocks of nucleic acids, consisting of a nitrogenous base, a sugar, and phosphate groups.
Substrate availability refers to the presence and concentration of substrates required for enzymatic reactions, impacting the rate and efficiency of metabolic processes. It plays a crucial role in determining how well metabolic pathways function, as enzymes rely on substrates to catalyze biochemical reactions. Variations in substrate availability can lead to changes in metabolic rates and can affect cellular energy production and overall metabolic balance.
Enzyme kinetics: The study of the rates of enzyme-catalyzed reactions and how they change in response to varying substrate concentrations.
Allosteric regulation: A process where the binding of a molecule at one site on an enzyme affects the enzyme's activity at a different site, influencing substrate binding and reaction rates.
Metabolic flux: The rate at which substrates and products flow through a metabolic pathway, influenced by substrate availability, enzyme activity, and other regulatory mechanisms.
Anabolic functions are metabolic processes that build complex molecules from simpler ones, requiring energy input in the form of ATP. These functions are crucial for growth, repair, and maintenance of tissues, as they contribute to the synthesis of proteins, nucleic acids, and other essential biomolecules. Understanding anabolic functions is vital for comprehending how cells utilize energy and resources to create macromolecules necessary for life.
catabolic functions: Metabolic processes that break down complex molecules into simpler ones, releasing energy that can be used by the cell.
ATP (adenosine triphosphate): The primary energy currency of the cell, providing the necessary energy for various biochemical reactions, including anabolic processes.
biosynthesis: The process by which living organisms produce complex compounds from simpler substrates, often involving enzymatic reactions and energy consumption.
Oxaloacetate is a four-carbon dicarboxylic acid that plays a critical role in the citric acid cycle, also known as the Krebs cycle. It acts as both a substrate and an intermediate, facilitating the conversion of acetyl-CoA into energy-rich compounds. Furthermore, oxaloacetate is important in carbohydrate metabolism and serves as a precursor for gluconeogenesis and amino acid synthesis, linking various metabolic pathways.
Acetyl-CoA: A two-carbon molecule derived from carbohydrates, fats, and proteins that enters the citric acid cycle to be metabolized for energy.
Gluconeogenesis: The metabolic process of synthesizing glucose from non-carbohydrate precursors, primarily occurring in the liver.
Citric Acid Cycle: A series of biochemical reactions that take place in the mitochondria, crucial for energy production through the oxidation of acetyl-CoA.
Citrate is a key intermediate in the citric acid cycle, also known as the Krebs cycle or tricarboxylic acid (TCA) cycle. It is formed by the condensation of acetyl-CoA with oxaloacetate, catalyzed by the enzyme citrate synthase. Citrate plays a vital role in cellular metabolism, serving as a precursor for various biosynthetic pathways and contributing to the regulation of energy production.
Acetyl-CoA: A central metabolite that serves as a key substrate in the citric acid cycle and is derived from the breakdown of carbohydrates, fats, and proteins.
Oxaloacetate: A four-carbon dicarboxylic acid that combines with acetyl-CoA to form citrate at the beginning of the citric acid cycle.
Citrate synthase: The enzyme responsible for catalyzing the formation of citrate from acetyl-CoA and oxaloacetate in the first step of the citric acid cycle.
Citrate synthase is an essential enzyme in the citric acid cycle that catalyzes the condensation of acetyl-CoA and oxaloacetate to form citrate. This reaction is a crucial step in energy production, linking carbohydrate, fat, and protein metabolism to ATP synthesis through oxidative phosphorylation.
Acetyl-CoA: A central metabolic intermediate that serves as a key substrate for various biochemical reactions, including the citric acid cycle.
Oxaloacetate: A four-carbon compound that combines with acetyl-CoA in the first step of the citric acid cycle, forming citrate.
Citric Acid Cycle: Also known as the Krebs cycle, it is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetyl-CoA.
Aconitase is an enzyme that plays a critical role in the citric acid cycle, catalyzing the isomerization of citrate to isocitrate through a two-step process. This enzyme is important for facilitating energy production in aerobic respiration and helps regulate the flow of metabolites within the cycle, impacting overall cellular metabolism.
Citric Acid Cycle: A series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetyl-CoA, producing ATP and electron carriers.
Isocitrate: A key intermediate in the citric acid cycle formed from citrate through the action of aconitase, which can be further processed to produce energy.
Enzyme Regulation: The process by which the activity of enzymes, such as aconitase, is controlled by various factors including substrate availability, product concentration, and allosteric effectors.
Isocitrate is a six-carbon intermediate compound in the citric acid cycle, formed from citrate by the enzyme aconitase. It plays a crucial role in energy production as it is further processed to produce NADH and ATP, contributing to cellular respiration and energy metabolism.
Citrate: Citrate is a six-carbon compound that is the first product of the citric acid cycle, formed from acetyl-CoA and oxaloacetate.
Aconitase: Aconitase is an enzyme that catalyzes the conversion of citrate to isocitrate, facilitating the isomerization process in the citric acid cycle.
NADH: NADH is a coenzyme that carries electrons to the electron transport chain, playing a key role in energy production during cellular respiration.
Isocitrate dehydrogenase is an important enzyme in the citric acid cycle that catalyzes the conversion of isocitrate to alpha-ketoglutarate while reducing NAD+ to NADH. This enzyme plays a critical role in energy production and cellular respiration, linking the cycles of glucose metabolism to the production of electron carriers for ATP synthesis.
Citric Acid Cycle: A series of enzymatic reactions that takes place in the mitochondria, converting acetyl-CoA into energy-rich compounds like NADH and FADH2 while producing CO2 as a waste product.
NAD+: Nicotinamide adenine dinucleotide, a coenzyme that acts as an electron carrier in cellular respiration, accepting electrons during metabolic reactions.
Alpha-ketoglutarate: A key intermediate in the citric acid cycle that serves as a substrate for several metabolic pathways and is important for amino acid synthesis.
α-ketoglutarate is a key intermediate in the citric acid cycle and a significant molecule in amino acid metabolism. It plays a crucial role in energy production, being involved in the conversion of carbohydrates, fats, and proteins into usable energy. Additionally, α-ketoglutarate acts as a precursor for several amino acids and is involved in the urea cycle, highlighting its importance in both energy production and nitrogen metabolism.
Glutamate: An amino acid that can be synthesized from α-ketoglutarate through transamination, playing a critical role in nitrogen metabolism.
Transamination: The process by which an amino group is transferred from an amino acid to a keto acid, forming a new amino acid and a new keto acid; α-ketoglutarate often serves as the keto acid in these reactions.
Succinyl-CoA: A product formed from α-ketoglutarate during the citric acid cycle, leading to further energy extraction from nutrients.
NAD+ (nicotinamide adenine dinucleotide) is a vital coenzyme that functions as an electron carrier in various metabolic reactions. It plays a critical role in redox reactions, helping to transfer electrons from one molecule to another, thus facilitating energy production in cellular processes such as glycolysis, the citric acid cycle, and fatty acid oxidation and synthesis. Its ability to exist in an oxidized form (NAD+) and a reduced form (NADH) is essential for maintaining the balance of metabolic pathways.
NADH: The reduced form of NAD+, which carries high-energy electrons and is produced during glycolysis, the citric acid cycle, and other metabolic pathways.
Redox Reaction: A chemical reaction involving the transfer of electrons between two species, crucial for energy production in metabolic processes.
Electron Transport Chain: A series of protein complexes located in the inner mitochondrial membrane that transfer electrons from NADH and FADH2 to oxygen, generating ATP in the process.
The α-ketoglutarate dehydrogenase complex is a multi-enzyme complex that catalyzes the conversion of α-ketoglutarate to succinyl-CoA in the citric acid cycle, also known as the Krebs cycle. This reaction is significant because it represents the third oxidative decarboxylation step in the cycle, where carbon dioxide is released and energy-rich NADH is produced. The regulation of this enzyme complex plays a crucial role in controlling the overall rate of the citric acid cycle and cellular metabolism.
Citric Acid Cycle: A series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins.
NADH: A coenzyme that acts as an electron carrier in cellular respiration, playing a critical role in the production of ATP during oxidative phosphorylation.
Succinyl-CoA: A four-carbon intermediate in the citric acid cycle formed from α-ketoglutarate that is further converted into succinate while producing GTP or ATP.
Decarboxylation is the biochemical process of removing a carboxyl group (-COOH) from a molecule, releasing carbon dioxide (CO2) in the process. This reaction is crucial in various metabolic pathways, particularly in the conversion of organic acids into more energetically favorable molecules during cellular respiration, including the citric acid cycle.
Citrate: A six-carbon compound formed when acetyl-CoA combines with oxaloacetate, serving as the starting point for the citric acid cycle.
Alpha-ketoglutarate: A five-carbon intermediate in the citric acid cycle that is formed by the decarboxylation of isocitrate.
NADH: A reduced coenzyme that acts as an electron carrier in cellular respiration, produced during various steps of the citric acid cycle including decarboxylation reactions.
Succinyl-CoA is a crucial intermediate in the citric acid cycle, formed from the conversion of α-ketoglutarate. This molecule plays a significant role in energy production and biosynthesis, connecting various metabolic pathways by facilitating the generation of ATP and serving as a substrate for the synthesis of heme and other biomolecules.
Acetyl-CoA: Acetyl-CoA is a key metabolic intermediate that feeds into the citric acid cycle and is generated from carbohydrates, fats, and proteins.
α-Ketoglutarate: α-Ketoglutarate is an intermediate in the citric acid cycle that is converted to succinyl-CoA through a reaction catalyzed by α-ketoglutarate dehydrogenase.
Succinate: Succinate is the product formed when succinyl-CoA is converted in the citric acid cycle, which then continues to be processed to regenerate oxaloacetate.
Succinyl-CoA synthetase is an enzyme that plays a critical role in the citric acid cycle by catalyzing the reversible conversion of succinyl-CoA to succinate, coupled with the phosphorylation of GDP to GTP or ADP to ATP. This reaction not only helps in energy production but also links various metabolic pathways, showcasing the importance of this enzyme in cellular respiration and metabolism.
Citric Acid Cycle: A series of enzymatic reactions that occurs in the mitochondria, generating energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins.
GTP: Guanosine triphosphate, a nucleotide that serves as a source of energy and a substrate for protein synthesis, produced during the action of succinyl-CoA synthetase.
Coenzyme A: A cofactor that plays a crucial role in the synthesis and oxidation of fatty acids and the metabolism of carbohydrates and amino acids, serving as a carrier of acyl groups.
Succinate is a four-carbon dicarboxylic acid that plays a key role in the citric acid cycle as an intermediate formed during the conversion of succinyl-CoA to succinate. This transformation is catalyzed by the enzyme succinyl-CoA synthetase, which also generates GTP or ATP, depending on the specific organism. Succinate serves as a crucial substrate for further reactions within the cycle, linking various metabolic pathways and influencing the regulation of cellular respiration.
Succinyl-CoA: A high-energy intermediate in the citric acid cycle, formed from the breakdown of fatty acids and amino acids, which is converted into succinate.
Fumarate: The product formed when succinate undergoes oxidation by succinate dehydrogenase in the citric acid cycle, facilitating the continuation of energy production.
GTP: Guanosine triphosphate, a nucleotide that acts as an energy currency in cells, produced during the conversion of succinyl-CoA to succinate in the citric acid cycle.
ATP, or adenosine triphosphate, is a high-energy molecule that serves as the primary energy currency of the cell. It is essential for driving various biochemical processes, including muscle contraction, active transport, and biosynthesis. ATP is produced in cellular respiration and photosynthesis, linking energy-releasing reactions to energy-consuming activities.
ADP: Adenosine diphosphate (ADP) is a molecule that is formed when ATP loses one of its phosphate groups, releasing energy for cellular processes.
Phosphorylation: The process of adding a phosphate group to a molecule, often mediated by enzymes, which can change the molecule's activity or function.
Oxidative Phosphorylation: A metabolic pathway that uses energy released by the electron transport chain to add a phosphate group to ADP, forming ATP in the mitochondria.
Succinate dehydrogenase is an enzyme that plays a crucial role in both the citric acid cycle and the electron transport chain. It catalyzes the conversion of succinate to fumarate while reducing flavin adenine dinucleotide (FAD) to FADH2. This enzyme links the citric acid cycle with oxidative phosphorylation, as the FADH2 produced is subsequently utilized in the electron transport chain to generate ATP through chemiosmosis.
FADH2: A reduced form of flavin adenine dinucleotide that serves as an electron carrier in the electron transport chain.
Citric Acid Cycle: A series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetate derived from carbohydrates, fats, and proteins.
Electron Transport Chain: A sequence of protein complexes and other molecules that transfer electrons through redox reactions to create a proton gradient that drives ATP synthesis.
Fumarate is a key intermediate in the citric acid cycle, formed from the dehydration of malate by the enzyme fumarase. It plays an important role in both energy production and the metabolism of amino acids, particularly during the conversion of certain amino acids to succinate and ultimately to fumarate, linking amino acid catabolism with the citric acid cycle.
Malate: Malate is a four-carbon dicarboxylic acid that is formed during the citric acid cycle, serving as a substrate for the conversion into fumarate.
Succinate: Succinate is another four-carbon dicarboxylic acid that is produced from fumarate in the citric acid cycle, further contributing to energy production.
Fumarase: Fumarase is an enzyme that catalyzes the reversible conversion of fumarate to malate, playing a critical role in the citric acid cycle.
FAD, or flavin adenine dinucleotide, is a redox cofactor involved in various metabolic reactions, particularly in the citric acid cycle. It serves as an electron carrier, accepting electrons during reactions and subsequently donating them in the electron transport chain, playing a crucial role in cellular respiration and energy production.
NAD+: NAD+, or nicotinamide adenine dinucleotide, is another important coenzyme that acts as an electron carrier in metabolic processes, similar to FAD but has a different structure and specific reactions.
Coenzyme A: Coenzyme A is a critical cofactor that plays a key role in the metabolism of fatty acids and the citric acid cycle by forming acetyl-CoA and facilitating the transfer of acyl groups.
Electron Transport Chain: The electron transport chain is a series of protein complexes located in the mitochondrial membrane that transfer electrons from electron donors to electron acceptors, generating ATP through oxidative phosphorylation.
Fumarase is an enzyme that catalyzes the reversible hydration of fumarate to malate in the citric acid cycle. This reaction is crucial for the continuation of the cycle, which plays a significant role in cellular respiration and energy production. Fumarase functions as a key player in the metabolic pathway that converts carbohydrates, fats, and proteins into usable energy, emphasizing its importance in cellular metabolism.
Citric Acid Cycle: A series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins.
Malate: A four-carbon dicarboxylic acid produced from fumarate during the citric acid cycle, which is then further oxidized to regenerate oxaloacetate.
Aconitase: An enzyme that catalyzes the conversion of citrate to isocitrate in the citric acid cycle, also playing a role in regulating metabolic pathways.
Malate is a four-carbon dicarboxylic acid that plays a crucial role in metabolic processes, particularly in the citric acid cycle and the transport of reducing equivalents across mitochondrial membranes. It serves as both an intermediate in energy production and as a key player in the C4 and CAM pathways of carbon fixation, connecting various metabolic pathways and facilitating cellular respiration and photosynthesis.
Oxaloacetate: A four-carbon molecule that combines with acetyl-CoA to form citrate in the first step of the citric acid cycle.
NADH: A reduced form of nicotinamide adenine dinucleotide, which acts as an electron carrier in cellular respiration, playing a key role in oxidative phosphorylation.
C4 Photosynthesis: A carbon fixation pathway that allows plants to efficiently capture CO2 and minimize photorespiration, using malate as an intermediate.
Malate dehydrogenase is an enzyme that catalyzes the reversible conversion of malate to oxaloacetate, utilizing NAD+ as a cofactor to produce NADH in the process. This reaction is crucial for cellular metabolism, as it plays a significant role in the citric acid cycle and also facilitates the transport of reducing equivalents into mitochondria through the malate-aspartate shuttle.
Citric Acid Cycle: A series of enzymatic reactions that convert acetyl-CoA into carbon dioxide and generate energy in the form of ATP, NADH, and FADH2.
NADH: A reduced coenzyme that carries electrons during cellular respiration, playing a key role in energy production within the mitochondria.
Malate-Aspartate Shuttle: A mechanism that transports electrons from the cytosol into the mitochondria, facilitating the transfer of reducing equivalents generated during glycolysis.
Substrate-level phosphorylation is a process in cellular metabolism where ATP is produced directly from the transfer of a phosphate group from a high-energy substrate to ADP, without the involvement of an electron transport chain. This mechanism is crucial for generating energy in both glycolysis and the citric acid cycle, providing a rapid way to produce ATP in the absence of oxygen or during anaerobic conditions.
ATP: Adenosine triphosphate (ATP) is the primary energy carrier in all living organisms, storing and transferring energy within cells.
Glycolysis: Glycolysis is the metabolic pathway that converts glucose into pyruvate, producing a small amount of ATP and NADH in the process.
Citric Acid Cycle: The citric acid cycle, also known as the Krebs cycle, is a series of chemical reactions used by all aerobic organisms to generate energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins.
Oxidative phosphorylation is the process by which ATP is produced in cells through the transfer of electrons from electron donors to electron acceptors in the electron transport chain, coupled with the generation of a proton gradient across the mitochondrial membrane. This process connects energy production from nutrients with the synthesis of ATP, highlighting its role in cellular respiration and energy metabolism.
Electron transport chain: A series of protein complexes and other molecules located in the inner mitochondrial membrane that facilitate the transfer of electrons and contribute to the generation of a proton gradient.
Chemiosmosis: The movement of protons across a selectively permeable membrane, down their electrochemical gradient, which drives ATP synthesis by ATP synthase.
ATP synthase: An enzyme complex that synthesizes ATP from ADP and inorganic phosphate using the energy derived from the flow of protons across the mitochondrial membrane.
Anaplerotic reactions are metabolic pathways that replenish the intermediates of the citric acid cycle (Krebs cycle), ensuring its continuous operation. These reactions are essential for maintaining the balance of metabolites within the cycle, allowing it to function efficiently in energy production and biosynthesis, especially during times when intermediates are drawn off for other metabolic processes.
Citric Acid Cycle: A series of biochemical reactions that take place in the mitochondria, responsible for converting carbohydrates, fats, and proteins into carbon dioxide and water while generating energy in the form of ATP.
Oxaloacetate: A four-carbon molecule that is an important intermediate in the citric acid cycle, which combines with acetyl-CoA to form citrate and is replenished through anaplerotic reactions.
Pyruvate Carboxylase: An enzyme that catalyzes the conversion of pyruvate to oxaloacetate, serving as a key anaplerotic reaction that helps maintain citric acid cycle intermediates.