Full Form of TCA, Products, Energetics, Inhibitors

The TCA full form is Tricarboxylic Acid Cycle. It is also the Kreb cycle after the name of popular chemist Sir Hans Adolf Krebs for his exemplary contribution towards this cycle. It is basically the second stage of cellular respiration that happens inside the matrix of mitochondria. 

The TCA cycle is basically a series of a chemical reaction through which aerobic organisms releases their energy. This energy is typically derived through the oxidation of acetyl CoA by converting fats, proteins and carbohydrates into Аdenоsine Triрhоsрhаte (АTР).

What is TCA Cycle?

TCA cycle or Tricarboxylic acid cycle is an eight steps process that aims to decompose organic compounds like amino acid, fatty acid, glucose, and sugar. This whole process is carried out inside the mitochondria cell during the second phase of cellular respiration. 

Soluble enzymes work as a catalyst to aid the TCA cycle. After the reaction is completed, bi-products namely, NADH and FADH2 are produced. Next, electrons are transferred to the next pathway. 

Generally, a TCA cycle is also called a cyclic route as the last step of this creation regenerates the pathway thus making it a closed loop only if oxygen is present in the cycle. 

Steps Involved in the TCA Cycle

TCA cycle is one of the complex reactions that happen inside the body of an anaerobic organism. A total of eight steps are present in this cycle making it very complex and difficult. Here in the space below, you can check the details associated with all the eight steps:

1. The TCA cycle commences with the condensation of oxaloacetate and the acetyl group of CoA. An oxaloacetate is a four-carbon unit whereas the CoA is a two-carbon unit. Both citrate and CoA are formed when oxaloacetate reacted with acetyl CoA and H2O. Subsequently, it is hydrolysed to produce citrate and CoA.
2. Next, the six-carbon unit undergoes oxidative decarboxylation and citrate is isomerised into isocitrate. During the isomerisation of citrate dehydration occurs first which is followed by a hydration stage.
3. In the third step, the oxidation of isocitrate happens. Due to this, molecules of carbon dioxide are emitted. After the reaction is over, a five-carbon molecule termed α -ketoglutarate is left. As a result, NAD+ is also converted to NADH and the enzyme isocitrate dehydrogenase acts as a catalyses.
4. In the fourth step, α-ketoglutarate is oxidised, after which NAD+ is reduced to NADH thus releasing a carbon dioxide molecule. The four-carbon molecule that is left behind makes up Coenzyme A and forms succinyl CoA which is an unstable chemical. This enzyme usually acts as a catalyses which is α-ketoglutarate dehydrogenase, for the Tricarboxylic Acid cycle.
5. The five steps consist of CoA of succinyl CoA which is a phosphate group that is later transferred to ADP to form ATP. In this step, GDP (Guanosine Diphosphate) is used to create GTP (Guanosine Triphosphate) in some cells. The end product is Succinate which is typically a four-carbon chemical.
6. Next, this succinate oxidises with oxygen thus forming a four-carbon molecule also known as fumarate, a four-carbon molecule. Further, FADH2 is formed by transferring two hydrogen molecules. This step usually happens in the inner membrane of the mitochondria.
7. In the seventh step, water is added to this carbon molecule that fumarates thus forming a four-carbon molecule also known as malate.
8. In the last step, this malate oxidises completely to regenerate oxaloacetate which is usually the last stage of the citric acid cycle.

End Products of a TCA Cycle

After the reaction is over, there are three end products that come out, find the details associated with the same below:

• 2 carbon dioxide molecules
• 3 NADH molecules, 3 hydrogen ions, and 1 FADH2 molecule
• 1 ATP/GTP molecule

Energetics of TCA Cycle

Research suggest that around three molecules of NADH and one of FADH2 combine together to produce one molecule of acetyl-CoA catabolized in one turn of the cycle. Here is the detailed table comprising the name of the reaction, the total number of ATPs and the production method.

Inhibitors of TCA Cycle

Here are some of the inhibitors of the TCA cycle:

• Aconitase inhibited by fluoroacetate.
• a-Ketoglutarate dehydrogenase inhibited by arsenite.
• Succinate dehydrogenase inhibited by malonate.

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