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Encyclopedia > Citric acid cycle
Overview of the citric acid cycle
Overview of the citric acid cycle

The citric acid cycle (also known as the tricarboxylic acid cycle, the TCA cycle, or the Krebs cycle, after Hans Adolf Krebs who identified the cycle) is a series of chemical reactions of central importance in all living cells that use oxygen as part of cellular respiration. In aerobic organisms, the citric acid cycle is part of a metabolic pathway involved in the chemical conversion of carbohydrates, fats and proteins into carbon dioxide and water to generate a form of usable energy. It is the third of four metabolic pathways that are involved in fuel molecule catabolism and ATP production, the other three being glycolysis and pyruvate oxidation before it, and respiratory chain after it. Image File history File links TCA.svg‎ Citric Acid Pathway. ... Image File history File links TCA.svg‎ Citric Acid Pathway. ... Sir Hans Adolf Krebs (August 25, 1900 – November 22, 1981) was a German, later British medical doctor and biochemist. ... A chemical reaction occurs when vapours of hydrogen chloride in a beaker and ammonia in a test tube meet to form a cloud of a new substance, ammonium chloride A chemical reaction is a process that results in the interconversion of chemical substances. ... Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell. Cells in culture, stained for keratin (red) and DNA (green). ... General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Atomic mass 15. ... Cellular Respiration is a process that describes the metabolic reactions and processes that take place in a cell to obtain chemical energy from fuel molecules. ... An aerobic organism or aerobe is an organism that has an oxygen based metabolism. ... In biochemistry, a metabolic pathway is a series of chemical reactions occurring within a cell, catalyzed by enzymes, resulting in either the formation of a metabolic product to be used or stored by the cell, or the initiation of another metabolic pathway (then called a flux generating step). ... Lactose is a disaccharide found in milk. ... For other uses, see Fat (disambiguation). ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Carbon dioxide is a chemical compound composed of one carbon and two oxygen atoms. ... Impact of a drop of water. ... A fuel molecule is a molecule metabolized by a cell to generate ATP. Types Carbohydrate Fat Protein ... Anabolism is the aspect of metabolism that contributes to growth. ... Adenosine 5-triphosphate (ATP) is a multifunctional nucleotide that is most important as a molecular currency of intracellular energy transfer. ... Glycolysis is a metabolic pathway by which a 6-carbon glucose (Glc) molecule is oxidized to two molecules of pyruvic acid (Pyr). ... It has been suggested that this article or section be merged into Pyruvate decarboxylation. ... The electron transfer chain (also called the electron transport chain, or simply electron transport), is a series of protein complexers and lipid messengers spanning the inner mitochondrial membrane that accepts electrons from electron donors such as NADH or succinate, shuttles these electrons from within the mitochondrial matrix across the inner...


The citric acid cycle also provides precursors for many compounds such as certain amino acids, and some of its reactions are therefore important even in cells performing fermentation. Phenylalanine is one of the standard amino acids. ... Fermentation in progress Fermentation is a process of energy production in a cell in an anaerobic environment (with no oxygen present). ...

Contents

Overview

The sum of all reactions in the citric acid cycle is:

Acetyl-CoA + 3 NAD+ + FAD + GDP + Pi + 1 H2O + 1 CoA-SH → 2 CoA-SH + 3 NADH + 3 H+ + FADH2 + GTP + 2 CO2

Two carbons are oxidized to CO2, and the energy from these reactions is stored in GTP, NADH and FADH2. NADH and FADH2 are coenzymes (molecules that enable or enhance enzymes) that store energy and are utilized in oxidative phosphorylation. The most fundamental reactions in chemistry are the redox processes. ... Guanosine triphosphate (GTP) is also known as guanosine-5-triphosphate. ... Coenzyme A Coenzymes are small organic non-protein molecules that carry chemical groups between enzymes. ... The Electron Transport Chain. ...

Step Substrate Enzyme Reaction type Reactants/
Coenzymes
Products/
Coenzymes
Comment
1 Oxaloacetate Citrate synthase Condensation Acetyl CoA +
H2O
CoA-SH
2 Citrate Aconitase Dehydration
3 cis-Aconitate Aconitase Hydration H2O
4 Isocitrate Isocitrate dehydrogenase Oxidation NAD+ NADH + H+
5 Oxalosuccinate Isocitrate dehydrogenase Decarboxylation H+ CO2
6 α-Ketoglutarate α-Ketoglutarate dehydrogenase Oxidative
decarboxylation
NAD+ +
CoA-SH
NADH + H+
+ CO2
7 Succinyl-CoA Succinyl-CoA synthetase substrate level phosphorylation GDP + Pi GTP +
CoA-SH
or ADP->ATP
8 Succinate Succinate dehydrogenase Oxidation FAD FADH2
9 Fumarate Fumarase Addition (H2O) H2O
10 L-Malate Malate dehydrogenase Oxidation NAD+ NADH + H+

A reactant or reagent is any substance initially present in a chemical reaction. ... Coenzyme A Coenzymes are small organic non-protein molecules that carry chemical groups between enzymes. ... The enzyme citrate synthase (E.C. 2. ... A condensation reaction (also known as a dehydration reaction or dehydration synthesis when water is lost) is a chemical reaction in which two molecules or moieties react and become covalently bonded to one another by the concurrent loss of a small molecule, often water, methanol, or a type of hydrogen... Citric acid is a weak organic acid found in citrus fruits. ... Aconitase (aconitate hydratase; EC 4. ... Dehydration (hypohydration) is the removal of water (hydro in ancient Greek) from an object. ... CIS usually refers to: Commonwealth of Independent States, a modern-day political entity consisting of 11 former Soviet Union Republics CIS is also an acronym for: Canadian Interuniversity Sport Cancer Information Service Carcinoma in situ Centre for Independent Studies Center for Immigration Studies Chinese International School Cisalpino Citizenship & Immigration Services... Aconitate is a substrate of the citric acid cycle. ... In chemistry, hydration is the condition of being combined with water. ... Isocitrate is a substrate of the citric acid cycle. ... Isocitrate dehydrogenase (EC 1. ... The most fundamental reactions in chemistry are the redox processes. ... Nicotinamide adenine dinucleotide (NAD+) Nicotinamide adenine dinucleotide (NAD+) and nicotinamide adenine dinucleotide phosphate (NADP) are two important cofactors found in cells. ... Oxalosuccinate is a substrate of the citric acid cycle. ... Isocitrate dehydrogenase (EC 1. ... A Decarboxylation is any chemical reaction in which a carboxyl group (-COOH) is split off from a compound as carbon dioxide (CO2). ... Carbon dioxide is a chemical compound composed of one carbon and two oxygen atoms. ... Ketoglutaric acid is used for either of two crystalline keto derivatives C5H6O5 of glutaric acid. ... Oxoglutarate dehydrogenase (aka α-ketoglutarate dehydrogenase) is an enzyme (EC 1. ... Acetyl Coenzyme A Acetyl-CoA Coenzyme A (CoA, CoASH, or HSCoA) is a coenzyme, notable for its role in the synthesis and oxidization of fatty acids, and the oxidation of pyruvate in the citric acid cycle. ... Carbon dioxide is a chemical compound composed of one carbon and two oxygen atoms. ... Categories: Biochemistry stubs ... Succinyl coenzyme A synthetase catalyzes the formation of succinyl-CoA, a 4-carbon metabolite, from succinate and coenzyme-A. Johnson et al. ... Substrate-level phosphorylation is a type of chemical reaction that results in the formation of adenosine triphosphate (ATP) by the direct transfer of a phosphate group to adenosine diphosphate (ADP) from a reactive intermediate. ... In chemistry, a phosphate is a polyatomic ion or radical consisting of one phosphorus atom and four oxygen. ... Guanosine triphosphate (GTP) is also known as guanosine-5-triphosphate. ... ADP may refer to: Among organizations and companies: Aéroports de Paris, airport authority for the Parisian region in France. ... ATP may refer to: Chemistry/Biochemistry Adenosine triphosphate, the universal energy currency of all living organisms Companies Alberta Theatre Projects, a major Canadian theatre company. ... Succinic acid, originally called spirit of amber, is a carboxylic acid with the formula: HOOC-CH2-CH2-COOH At room temperature, pure succinic acid is a solid that forms colorless, odorless prisms. ... Succinate - coenzyme Q reductase also called succinate dehydrogenase is an enzyme complex found in the matrix part of the inner mitochondrial membrane. ... In biochemistry, flavin adenine dinucleotide (FAD) is the precursor molecule to FADH2. ... A fumarate is a salt or ester of fumaric acid. ... Fumarase is an enzyme involved in the Krebs Cycle that catalyzes the hydration (addition of H2O across a double bond) of Fumarate to L-malate (the natural optical isomer of a protein as apposed to the d isomer) Fumarase Deficiency In humans, Fumarase Deficiency is an enzyme irregularity that causes... Impact of a drop of water. ... Malic acid is a tart-tasting organic acid that plays a role in many sour or tart foods. ... Categories: Biochemistry stubs | EC 1. ...

A simplified view of the process

  • The citric acid cycle begins with Acetyl-CoA transfering its two-carbon acetyl group to the four-carbon acceptor compound, oxaloacetate, forming citrate, a six-carbon compound.
  • The citrate then goes through a series of chemical transformations, losing first one, then a second carboxyl group as CO2.
  • Most of the energy made available by the oxidative steps of the cycle is transferred as energy-rich electrons to NAD+, forming NADH. For each acetyl group that enters the citric acid cycle, three molecules of NADH are produced.
  • Electrons are also transferred to the electron acceptor FAD, forming FADH2.
  • At the end of each cycle, the four-carbon oxaloacetate has been regenerated, and the cycle continues. Products of the first turn of the cycle are one GTP, three NADH, one FADH2, and two CO2.
  • Because two acetyl-CoA molecules are produced from each glucose molecule, two cycles are required per glucose molecule.
  • At the end of all cycles, the products are two GTP, six NADH, two FADH2, four CO2.

Categories: Biochemistry stubs | Thiols ... General Name, Symbol, Number carbon, C, 6 Chemical series nonmetals Group, Period, Block 14, 2, p Appearance black (graphite) colorless (diamond) Atomic mass 12. ... Acetyl is the radical of acetic acid. ... Chemical strucutre of citric acid. ... A chemical substance is any material substance used in or obtained by a process in chemistry: A chemical compound is a substance consisting of two or more chemical elements that are chemically combined in fixed proportions. ... A carboxyl or carboxylic group is a functional group consisting of a carbon atom and an oxygen atom doubly bonded to each other. ... Properties The electron (also called negatron, commonly represented as e−) is a subatomic particle. ... Nicotinamide adenine dinucleotide (NAD+) Nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) are two important coenzymes found in cells. ... Acetyl is the radical of acetic acid. ... Nicotinamide adenine dinucleotide (NAD+) Nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) are two important coenzymes found in cells. ... Properties The electron (also called negatron, commonly represented as e−) is a subatomic particle. ... e- redirects here. ... In biochemistry, flavin adenine dinucleotide (FAD) is the precursor molecule to FADH2. ... General Name, Symbol, Number carbon, C, 6 Chemical series nonmetals Group, Period, Block 14, 2, p Appearance black (graphite) colorless (diamond) Atomic mass 12. ... GTP may stand for: Guanosine triphosphate GPRS Tunnelling Protocol Go Text Protocol Graduate Teacher Programme GTPlanet. ... Nicotinamide adenine dinucleotide (NAD+) Nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) are two important coenzymes found in cells. ... Categories: Biochemistry stubs | Thiols ... In science, a molecule is the smallest particle of a pure chemical substance that still retains its chemical composition and properties. ... Glucose (Glc), a monosaccharide (or simple sugar), is the most important carbohydrate in biology. ... In chemistry, a molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical bonds [1] [2] [3] [4] [5]. Chemical substances are not infinitely divisible into smaller fractions of the same substance: a molecule is generally considered the smallest particle of a pure... Glucose (Glc), a monosaccharide (or simple sugar), is the most important carbohydrate in biology. ... In chemistry, a molecule is an aggregate of two or more atoms in a definite arrangement held together by chemical bonds [1] [2] [3] [4] [5]. Chemical substances are not infinitely divisible into smaller fractions of the same substance: a molecule is generally considered the smallest particle of a pure... Nicotinamide adenine dinucleotide (NAD+) Nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) are two important coenzymes found in cells. ...

Regulation

Although pyruvate dehydrogenase is not technically a part of the citric acid cycle, its regulation is included here.


Many of the enzymes in the TCA cycle are regulated by negative feedback from ATP when the energy charge of the cell is high. Such enzymes include the pyruvate dehydrogenase, citrate synthase, isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase. These enzymes, which regulate the first three steps of the TCA cycle, are inhibited by high concentrations of ATP. This regulation ensures that the TCA cycle will not oxidise excessive amounts of pyruvate and acetyl-CoA when ATP in the cell is plentiful. This type of negative regulation by ATP is by an allosteric mechanism. Ribbon diagram of the enzyme TIM, surrounded by the space-filling model of the protein. ... Energy charge is one of several ways to represent the energy status of a cell. ... Pyruvate dehydrogenase is an enzyme (E1) in the pyruvate dehydrogenase complex (PDC). ... The enzyme citrate synthase (E.C. 2. ... Isocitrate dehydrogenase (EC 1. ... Oxoglutarate dehydrogenase (aka α-ketoglutarate dehydrogenase) is an enzyme (EC 1. ... In biochemistry, an enzyme or other protein is allosteric if its activity or efficiency changes in response to the binding of an effector molecule at a so-called allosteric site. ...


Several enzymes are also negatively regulated when the level of reducing equivalents in a cell are high (high ratio of NADH/NAD+). This mechanism for regulation is due to substrate inhibition by NADH of the enzymes that use NAD+ as a substrate. This includes pyruvate dehydrogenase, citrate synthase, isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase. Ribbon diagram of the enzyme TIM, surrounded by the space-filling model of the protein. ...


Calcium is used as a regulator. It activates pyruvate dehydrogenase, isocitrate dehydrogenase and oxoglutarate dehydrogenase.[citation needed] This increases the reaction rate of many of the steps in the cycle, and therefore increases flux throughout the pathway.


Citrate is used for feedback inhibition, as it inhibits the phosphofructokinase(enzyme in glycolysis) that makes Fructose 1,6-bisphosphate), a precursor of pyruvate. This prevents a constant high rate of flux when there is a build up of citrate and a decrease in substrate for the enzyme. Phosphofructokinase (PFK) is the most important regulatory enzyme (EC 2. ... Glycolysis is a metabolic pathway by which a 6-carbon glucose (Glc) molecule is oxidized to two molecules of pyruvic acid (Pyr). ... Fructosephosphates are sugar phosphates based upon fructose. ...


Major metabolic pathways converging on the TCA cycle

Most of the body's catabolic pathways converge on the TCA cycle, as the diagram shows. Reactions that form intermediates of the cycle are called anaplerotic reactions. Anabolism is the aspect of metabolism that contributes to growth. ... - of Greek origin, meaning to fill up Anaplerotic reactions are those that form intermediates of the TCA or citric acid cycle. ...


The citric acid cycle is the third step in carbohydrate catabolism (the breakdown of sugars). Glycolysis breaks glucose (a six-carbon-molecule) down into pyruvate (a three-carbon molecule). In eukaryotes, pyruvate moves into the mitochondria. It is converted into acetyl-CoA by decarboxylation and enters the citric acid cycle. Carbohydrate catabolism is the breakdown of carbohydrates into smaller units. ... Glycolysis is a metabolic pathway by which a 6-carbon glucose (Glc) molecule is oxidized to two molecules of pyruvic acid (Pyr). ... Glucose (Glc), a monosaccharide (or simple sugar), is the most important carbohydrate in biology. ... Pyruvate (CH3COCOO−) is the ionized form of pyruvic acid. ... Kingdoms Animalia - Animals Fungi Plantae - Plants Protista Alternative Phylogeny Unikonta    Opisthokonta    Amoebozoa Bikonta    Apusozoa    Cabozoa       Rhizaria       Excavata    Corticata       Archaeplastida       Chromalveolata Animals, plants, fungi, and protists are eukaryotes (IPA: ), organisms with a complex cell or cells, where the genetic material is organized into a membrane-bound nucleus or nuclei. ... In cell biology, a mitochondrion is an organelle found in the cells of most eukaryotes. ... The Pyruvate decarboxylation reaction links the metabolic pathways glycolysis and the citric acid cycle. ...


In protein catabolism, proteins are broken down by protease enzymes into their constituent amino acids. These amino acids are brought into the cells and can be a source of energy by being funnelled into the citric acid cycle. Protein catabolism is the breakdown of proteins into amino acids and simple derivative compounds, for transport into the cell through the plasma membrane and ultimately for the polymerisation into new proteins via the use of ribonucleic acids (RNA) and ribosomes. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Proteases (proteinases, peptidases, or proteolytic enzymes) are enzymes that break peptide bonds between amino acids of proteins. ... Ribbon diagram of the enzyme TIM, surrounded by the space-filling model of the protein. ... Phenylalanine is one of the standard amino acids. ...


In fat catabolism, triglycerides are hydrolyzed to break them into fatty acids and glycerol. In the liver the glycerol can be converted into glucose via dihydroxyacetone phosphate and glyceraldehyde-3-phosphate by way of gluconeogenesis. In many tissues, especially heart tissue, fatty acids are broken down through a process known as beta oxidation which results in acetyl-CoA which can be used in the citric acid cycle. Sometimes beta oxidation can yield propionyl CoA which can result in further glucose production by gluconeogenesis in liver. Fatty acids are an important source of energy for many organisms. ... It has been suggested that Medium Chain Triglycerides be merged into this article or section. ... Hydrolysis is a chemical reaction or process in which a molecule is split into two parts by reacting with a molecule of water, which has the chemical formula H2O. One of the parts gets an OH- from the water molecule and the other part gets an H+ from the water. ... In chemistry, especially biochemistry, a fatty acid is a carboxylic acid often with a long unbranched aliphatic tail (chain), which is either saturated or unsaturated. ... Glycerol, also well known as glycerin and glycerine, and less commonly as propane-1,2,3-triol, 1,2,3-propanetriol, 1,2,3-trihydroxypropane, glyceritol, and glycyl alcohol is a colorless, odorless, hygroscopic, and sweet-tasting viscous liquid. ... Pyruvic acid Oxaloacetic acid Phosphoenolpyruvate Fructose 1,6-bisphosphate Fructose 6-phosphate Glucose-6-phosphate Glucose Gluconeogenesis is the generation of glucose from non-sugar carbon substrates like pyruvate, lactate, glycerol, and amino acids (primarily alanine and glutamine). ... Beta oxidation is the process by which fats, in the form of Acyl-CoA molecules, are broken down in the mitochondria to generate Acetyl-CoA, the entry molecule for the Krebs Cycle. ... Pyruvic acid Oxaloacetic acid Phosphoenolpyruvate Fructose 1,6-bisphosphate Fructose 6-phosphate Glucose-6-phosphate Glucose Gluconeogenesis is the generation of glucose from non-sugar carbon substrates like pyruvate, lactate, glycerol, and amino acids (primarily alanine and glutamine). ...


The citric acid cycle is always followed by oxidative phosphorylation. This process extracts the energy from NADH and FADH2, recreating NAD+ and FAD, so that the cycle can continue. The citric acid cycle itself does not use oxygen, but oxidative phosphorylation does. The Electron Transport Chain. ...


The total energy gained from the complete breakdown of one molecule of glucose by glycolysis, the citric acid cycle and oxidative phosphorylation equals about 36 ATP molecules. The citric acid cycle is called an amphibolic pathway because it participates in both catabolism and anabolism. Glycolysis is a metabolic pathway by which a 6-carbon glucose (Glc) molecule is oxidized to two molecules of pyruvic acid (Pyr). ... The Electron Transport Chain. ... Amphibolic relates to a biochemical pathway that involves both catabolism and anabolism. ... Anabolism is the aspect of metabolism that contributes to growth. ... Anabolism is the metabolic process that builds larger molecules from smaller ones. ...


See also

Oxidative decarboxylation is the name given to the preparation of pyruvate, a product of glycolysis, for entrance into the Citric Acid Cycle (a. ... Citric acid is a weak organic acid found in citrus fruits. ... Glycolysis is a metabolic pathway by which a 6-carbon glucose (Glc) molecule is oxidized to two molecules of pyruvic acid (Pyr). ... The Pyruvate decarboxylation reaction links the metabolic pathways glycolysis and the citric acid cycle. ... The Electron Transport Chain. ... reverse krebs cycle ... Sir Hans Adolf Krebs (August 25, 1900 – November 22, 1981) was a German, later British medical doctor and biochemist. ...

References

  • Campbell, Reece: Biology (seventh edition). Benjamin Cummings, 2005.
  • Solomon, E.P., Berg, L.R., Martin, D.W., Biology, 7th Edition, Thompson Learning, 2005.

External links


 v  d  e 
Citric Acid Cycle Metabolic Pathway
Oxaloacetate Malate Fumarate Succinate Succinyl-CoA
Acetyl-CoA NADH + H+ NAD+ H2O FADH2 FAD CoA + ATP(GTP) Pi + ADP(GDP)
+ H2O NADH + H+ + CO2
CoA NAD+
H2O H2O NAD(P)+ NAD(P)H + H+ CO2
Citrate cis-Aconitate Isocitrate Oxalosuccinate Alpha-ketoglutarate

Ball-and-stick model of β-D-glucuronic acid The α-D form of glucuronic acid. ... A pentose is a monosaccharide with five carbon atoms. ... Inositol, (of which the most prominent naturally-ocurring form is myo-inositol, cis-1,2,3,5-trans-4,6-cyclohexanehexol), is a carbocyclic polyol that plays an important role as the structural basis for a number of secondary messengers in eukaryotic cells, including inositol phosphates, phosphatidylinositol (PI) and phosphatidylinositol... The pentose phosphate pathways Nonoxidative phase The pentose phosphate pathway (also called Phosphogluconate Pathway, or Hexose Monophosphate Shunt [HMP shunt]) is a process that serves to generate NADPH and the synthesis of pentose (5-carbon) sugars. ... Glycolysis is a metabolic pathway by which a 6-carbon glucose (Glc) molecule is oxidized to two molecules of pyruvic acid (Pyr). ... Pyruvic acid Oxaloacetic acid Phosphoenolpyruvate Fructose 1,6-bisphosphate Fructose 6-phosphate Glucose-6-phosphate Glucose Gluconeogenesis is the generation of glucose from non-sugar carbon substrates like pyruvate, lactate, glycerol, and amino acids (primarily alanine and glutamine). ... Glucosamine Sialic acid In chemistry, an amino sugar contains an amine group in place of a hydroxyl group. ... leucine isoleucine valine The phrase branched-chain amino acids or BCAA is sometimes used to refer to the amino acids having aliphatic side-chains that are non-linear. ... This article or section does not cite its references or sources. ... The histidine bound haem group of succinate dehydrogenase, an electron carrier in the mitochondrial electron transfer chain. ... phenylalanine tryptophan tyrosine thyroxine Aromatic amino acids are amino acids which include an aromatic ring. ... The Pyruvate decarboxylation reaction links the metabolic pathways glycolysis and the citric acid cycle. ... Anaerobic respiration refers to the oxidation of molecules in the absence of oxygen to produce energy. ... Fatty acids are an important source of energy for many organisms. ... The Urea Cycle is a cycle of biochemical reactions occurring in many animal organisms that produces urea from ammonia. ... Pyrimidine biosynthesis occurs both in the body and through organic synthesis. ... Image File history File links Gtk-dialog-info. ... Image File history File links Metabolism_790px. ...


  Results from FactBites:
 
Krebs cycle: Definition and Much More from Answers.com (1719 words)
Synonyms: Krebs cycle, Krebs citric acid cycle, tricarboxylic acid cycle
The citric acid cycle (also known as the tricarboxylic acid cycle, the TCA cycle, or the Krebs cycle) is a series of chemical reactions of central importance in all living cells that utilize oxygen as part of cellular respiration.
In aerobic organisms, the citric acid cycle is part of a metabolic pathway involved in the chemical conversion of carbohydrates, fats and proteins into carbon dioxide and water to generate a form of usable energy.
  More results at FactBites »

 
 

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