Because during the TCA Cycle (aka Kreb’s Cycle), energy is both consumed and produced. During the TCA cycle, acetyl coA is converted to CO2 and H2O but. The citric acid cycle is the central metabolic hub of the cell. It is the final common pathway for the oxidation of fuel molecule such as amino acids. Amphibolic Nature Of TCA Cycle: In aerobic organisms, the citric acid cycle is an amphibolic pathway, one that serves in both catabolic and anabolic processes.
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The citric acid cycle is the central metabolic hub of the cell. It is the gateway to the aerobic metabolism of any molecule that can be transformed into an acetyl group or dicarboxylic acid. The cycle is also an important source of precursors, not only for the storage forms of cyce, but also for the building blocks of many natuee molecules such as amino acids, nucleotide bases, cholesterol, and porphyrin the organic component of heme.
Amphibolic Nature of TCA Cycle
TCA cycle is vital since none of the enzyme deficiencies have so far been encountered perhaps the enzyme deficiencies are incompatible with life. Indirect evidence of its importance for life can be considered form the fact that the inhibitors of Ammphibolic cycle act as poisons. The citric acid cycle Krebs cycle, Tricarboxylic acid cycle includes a series of oxidation-reduction reactions in mitochondria that result in the oxidation of an acetyl group to two molecules of carbon dioxide and reduce the coenzymes that are reoxidized through the electron transport chain, linked to the formation of ATP.
A four- carbon compound oxaloacetate condenses with a two-carbon acetyl unit to yield a six-carbon tricarboxylic acid citrate.
An isomer of citrate is then oxidatively decarboxylated. Oxaloacetate is then regenerated from succinate.
Two carbon atoms enter the cycle as an acetyl unit and two carbon atoms leave the cycle in the form of two molecules of carbon dioxide.
The four-carbon molecule, oxaloacetate that initiates the first step in the citric acid cycle is regenerated at the end of one passage through the cycle. The oxaloacetate acts catalytically: Thus, one molecule of oxaloacetate is capable of participating in the oxidation of many acetyl molecules.
Glucose, fatty acids, and most amino acids are metabolized to acetyl-CoA or intermediates of the cycle. As a result of oxidations catalyzed by the dehydrogenases of the citric acid cycle, three molecules of NADH and one of FADH2 are produced for each molecule of acetyl-CoA catabolized in one turn of the cycle. Thus, 1 acetate unit generates approximately 12 molecules of ATP. In dramatic contrast, only 2 molecules of ATP are generated per molecule of glucose which generates 2 molecules of acetyl CoA by anaerobic glycolysis.
Figure showing process of energy release from TCA cycle by oxidative phosphorylation. B Anabolic role- As a major metabolic hub nathre the cell, the citric acid cycle also provides intermediates for biosynthesis of various compounds.
Amphibolic nature of Krebs Cycle. How what we are is what we eat
Net transfer into the cycle occurs as a result of several reactions. This reaction is important in maintaining an adequate concentration of oxaloacetate for the condensation reaction with acetyl-CoA. If acetyl-CoA accumulates, it acts as both an allosteric activator of pyruvate carboxylase and an inhibitor of pyruvate dehydrogenase, thereby ensuring a supply of oxaloacetate. Lactate, an important substrate for gluconeogenesis, enters the cycle via oxidation to pyruvate and then carboxylation to oxaloacetate.
Semester paper- TCA cycle- Vital and Amphibolic | Biochemistry for Medics – Lecture Notes
Other amino acids contribute to gluconeogenesis because their carbon skeletons give rise to citric acid cycle intermediates. The conversion of propionate to succinyl-CoA via the Methylmalonyl-CoA pathway is also important for gluconeogenesis.
Figure showing the formation of non essential amino acids from the TCA cycle intermediates. Glutamine can also be utilized for the synthesis of purine nucleotides. Figure anture the formation of non essential amino acids from TCA cycle intermediates. Pyruvate dehydrogenase is a mitochondrial enzyme, and fatty-acid synthesis is a cytosolic pathway; the mitochondrial membrane is impermeable to acetyl-CoA.
Acetyl co A can also be used for the synthesis of Acetyl choline, cholesterol, steroids, ketone bodies, and is also required for detoxification reactions etc. Figure showing transportation of citrate out of mitochondrion to provide Acetyl co A for fatty acid or cholesterol synthesis.
Citrate is only available for transport out of the mitochondrion when Aconitase is saturated with its substrate, and citrate cannot be channeled directly from citrate synthase onto Aconitase. This ensures that citrate is used for fatty acid synthesis only when there is an adequate amount to ensure continued activity of the cycle.
Amohibolic regulates rate of glycolysis also, it acts as a negative modifier for PFK-1 enzyme and thus inhibits Glycolysis. Succinyl co A is required for the utilization of ketone bodies. It also acts as neuro transmitter.
Amphibolic nature of Krebs Cycle. How what we are is what we eat – PDF
Figure showing the bio synthetic role of TCA cycle. Thus, the intermediates of TCA cycle are utilized in both waysthey are oxidized to yield energy or are utilized for bio synthetic reactions depending upon the need of the body. Published December 8, By Dr.