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Page "Mitochondrion" ¶ 40
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citric and acid
The other product of transamidation is a keto acid that enters the citric acid cycle.
Further separation was carried out in the presence of a citric acid / ammonium buffer solution in a weakly acidic medium ( pH ≈ 3. 5 ), using ion exchange at elevated temperature.
These techniques allowed for the discovery and detailed analysis of many molecules and metabolic pathways of the cell, such as glycolysis and the Krebs cycle ( citric acid cycle ).
The two molecules acetyl-CoA ( from one molecule of glucose ) then enter the citric acid cycle, producing two more molecules of ATP, six more NADH molecules and two reduced ( ubi ) quinones ( via FADH < sub > 2 </ sub > as enzyme-bound cofactor ), and releasing the remaining carbon atoms as carbon dioxide.
Intermediate products of glycolysis, the citric acid cycle, and the pentose phosphate pathway can be used to make all twenty amino acids, and most bacteria and plants possess all the necessary enzymes to synthesize them.
Experiments have shown that two fungal strains ( Aspergillus niger, Penicillium simplicissimum ) were able to mobilize Cu and Sn by 65 %, and Al, Ni, Pb, and Zn by more than 95 %. Aspergillus niger can produce some organic acids such as citric acid.
*** energy pathways: fermentation — glycolysis — cellular respiration — citric acid cycle — photosynthesis — Calvin cycle
Other important natural examples are citric acid ( in lemons ) and tartaric acid ( in tamarinds ).
Overview of the citric acid cycle ( click to enlarge )
The citric acid cycle — also known as the tricarboxylic acid cycle ( TCA cycle ), the Krebs cycle, or the Szent-Györgyi – Krebs cycleis a series of chemical reactions used by all aerobic organisms to generate energy through the oxidization of acetate derived from carbohydrates, fats and proteins into carbon dioxide.
The name of this metabolic pathway is derived from citric acid ( a type of tricarboxylic acid ) that is first consumed and then regenerated by this sequence of reactions to complete the cycle.
In eukaryotic cells, the citric acid cycle occurs in the matrix of the mitochondrion.
The components and reactions of the citric acid cycle were established in the 1930s by seminal work from the Nobel laureates Albert Szent-Györgyi and Hans Adolf Krebs.
The citric acid cycle is a key component of the metabolic pathway by which all aerobic organisms generate energy.
Acetyl-CoA along with two equivalents of water ( H < sub > 2 </ sub > O ) are consumed by the citric acid cycle producing two equivalents of carbon dioxide ( CO < sub > 2 </ sub >) and one equivalent of HS-CoA.
The NADH and QH < sub > 2 </ sub > that is generated by the citric acid cycle is in turn used by the oxidative phosphorylation pathway to generate energy-rich adenosine triphosphate ( ATP ).
The product of this reaction, acetyl-CoA, is the starting point for the citric acid cycle.
* The citric acid cycle begins with the transfer of a two-carbon acetyl group from acetyl-CoA to the four-carbon acceptor compound ( oxaloacetate ) to form a six-carbon compound ( citrate ).
The carbons donated by acetyl-CoA become part of the oxaloacetate carbon backbone after the first turn of the citric acid cycle.
Loss of the acetyl-CoA-donated carbons as CO < sub > 2 </ sub > requires several turns of the citric acid cycle.
However, because of the role of the citric acid cycle in anabolism, they may not be lost, since many TCA cycle intermediates are also used as precursors for the biosynthesis of other molecules.

citric and acetyl-CoA
The citric acid cycle is continuously supplied with new carbon in the form of acetyl-CoA, entering at step 1 below.
Acetate is used by the muscle cells to produce acetyl-CoA using the enzyme acetyl-CoA synthetase, and the acetyl-CoA is then used in the citric acid cycle.
The acetyl-CoA is then ultimately converted into ATP, CO < sub > 2 </ sub >, and H < sub > 2 </ sub > O using the citric acid cycle and the electron transport chain.
The acetyl-CoA is the primary substrate to enter the citric acid cycle, also known as the tricarboxylic acid ( TCA ) cycle or Krebs cycle.
Ketone bodies are transported from the liver to other tissues, where acetoacetate and beta-hydroxybutyrate can be reconverted to acetyl-CoA to produce energy, via the citric acid cycle.
Unable to be used in the citric acid cycle, the excess acetyl-CoA is therefore rerouted to ketogenesis.
In the brain, these ketone bodies are then incorporated into acetyl-CoA and used in the citric acid cycle.
Despite these findings, it is considered unlikely that the 2-carbon acetyl-CoA derived from the oxidation of fatty acids would produce a net yield of glucose via the citric acid cycle.
Under normal conditions, acetyl-CoA is further oxidized and its energy transferred as electrons to NADH, FADH < sub > 2 </ sub >, and ATP in the citric acid cycle ( TCA cycle ).
* When the body has ample carbohydrates available as energy source, glucose is completely oxidized to CO < sub > 2 </ sub >; acetyl-CoA is formed as an intermediate in this process, first entering the citric acid cycle followed by complete conversion of its chemical energy to ATP in oxidative phosporylation.
Acetyl-CoA is not being recycled through the citric acid cycle because the citric acid cycle intermediates ( mainly oxaloacetate ) have been depleted to feed the gluconeogenesis pathway, and the resulting accumulation of acetyl-CoA activates ketogenesis.
Beta-oxidation is the process by which fatty acids, in the form of acyl-CoA molecules, are broken down in mitochondria and / or peroxisomes to generate acetyl-CoA, the entry molecule for the citric acid cycle.

citric and carbon
The three carbon pyruvate molecule loses a carbon atom and is shepherded into the citric acid cycle by coenzyme A.
Transamination or deamination of amino acids facilitates entering of their carbon skeleton into the cycle directly ( as pyruvate or oxaloacetate ), or indirectly via the citric acid cycle.
The carbon fixation metabolism became autocatalytic by forming a metabolic cycle in the form of a primitive sulfur-dependent version of the reductive citric acid cycle.
C. albidus is able to use glucose, citric acid, maltose, sucrose, trehalose, salicin, cellobiose, and inositol, as well as many other compounds, as sole carbon sources.
Though important to the overall effect of the medication, the aspirin ( acetylsalicylic acid ) is not required to produce the effervescent action of Alka-Seltzer ; the effervescence is produced by the baking soda ( sodium bicarbonate ) and citric acid reacting to form sodium citrate and carbon dioxide gas.
Prior to the citric acid cycle, pyruvic acid generated from glycolysis is converted into acetyl coenzyme A ( acetyl CoA ) by losing a carbon dioxide molecule.

citric and dioxide
The lemons that were not saleable as produce were made into pectin or citric acid, with sulfur dioxide used as a preservative.

citric and process
A typical passivation process of cleaning stainless steel tanks involves cleaning with sodium hydroxide and citric acid followed by nitric acid ( up to 20 % at 120 ° F ) and a complete water rinse.
This process involves boiling water and sugar together on a low heat, then adding fruit juice and lemon juice ( or citric acid ).
Some fruits, like quince, require an additive to start the fermentation process ( e. g., citric acid ).
Because it cannot be completely metabolized in the citric acid cycle, the products of its partial reaction must be removed in a process called cataplerosis.
This allows regeneration of the citric acid cycle intermediates, possibly an important process in certain metabolic diseases.

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