TCA Cycle Full Form

The TCA cycle (Krebs cycle or the citric acid cycle) is the second stage of the three-step process. Living cells breakdown organic fuel molecules in the presence of oxygen to capture the energy they need to grow and divide. Almost all plants, animals, fungi, and bacteria go through this metabolic process. The TCA cycle occurs in the network of intracellular structures known as mitochondria in all organisms except bacteria.

What is TCA Cycle?

TCA’s full form is Tricarboxylic Acid. The TCA cycle, or Tricarboxylic Acid Cycle, is a sequence of chemical events that occur in the cells of all aerobic organisms to release energy stored in the form of ATP by converting Acetyl CoA obtained from carbs, lipids, and proteins. Tricarboxylic Acid Cycle also known as the Citric Acid Cycle, and it happens in mitochondria during cellular respiration’s second phase. Soluble enzymes catalyse the TCA cycle’s processes. This ubiquitous anaerobic route produces NADH and FADH2. Each of these electrons is transferred to the next pathway, resulting in oxidation. Transfer oxidation will not occur without the electron. As a result, TCA Cycle generates fewer ATP or energy molecules directly. It’s also a cyclic route since the last step regenerates the pathway’s beginning molecules, making it a closed loop. It happens when there is oxygen present.

Krebs Cycle

TCA cycle is also known as Krebs Cycle. Sir Hans Adolf Krebs, a British biochemist, proposed the TCA Cycle, or Citric Acid Cycle. Krebs was recognised for his work after elucidating most of the reactions in this route. In addition, Fritz Lipmann and Nathan Kaplan found Coenzyme A later, allowing other researchers to complete the cycle as we know it today.

TCA Cycle

The TCA cycle is an eight-step cycle that aids in decomposing organic compounds. Glucose, sugars, fatty acids, amino acids, and other macromolecules cannot enter the TCA cycle directly. As a result, they are initially decomposed into the two-carbon molecule Acetyl CoA. After entering the TCA cycles, acetyl CoA passes through chemical reactions to create carbon dioxide and energy. A soluble enzyme catalyses each step of the process.

Steps in the TCA cycle

1. The Tricarboxylic Acid cycle begins with the condensation of oxaloacetate, a four-carbon unit, and the acetyl group of acetyl CoA, a two-carbon unit. Citrate and CoA are formed when oxaloacetate interacts with acetyl CoA and H2O. Oxaloacetate reacts with acetyl CoA to make citryl CoA, which is subsequently hydrolysed to produce citrate and CoA.
2. To allow the six-carbon unit to undergo oxidative decarboxylation, citrate is isomerised into isocitrate. A dehydration stage is followed by a hydration step in the isomerisation of citrate.
3. The oxidation of isocitrate happens in the third stage. With the emission of a molecule of carbon dioxide, a five-carbon molecule termed α -ketoglutarate is left behind. As a result, NAD+ is also converted to NADH. The enzyme isocitrate dehydrogenase catalyses this process.
4. The fourth step is quite similar to the third step. In this situation, α-ketoglutarate is oxidised, reducing NAD+ to NADH while also releasing a carbon dioxide molecule. The remaining four-carbon molecule takes up Coenzyme A and forms succinyl CoA, an unstable chemical. The enzyme that catalyses this step, α-ketoglutarate dehydrogenase, is critical for Tricarboxylic Acid cycle control.
5. The CoA of succinyl CoA is replaced by a phosphate group in step five, which is subsequently transferred to ADP to form ATP. GDP (guanosine diphosphate) is utilised instead of ADP to create GTP (guanosine triphosphate) in some cells. Succinate is the four-carbon chemical formed in this step.
6. In step six, succinate is oxidised, yielding fumarate, a four-carbon molecule. Two hydrogen atoms with their electrons are transferred to FAD in this process, resulting in FADH2. FADH2 may transfer its electrons directly into the electron transport chain because the enzyme that performs this step is situated in the mitochondrion’s inner membrane.
7. Water is added to the four-carbon molecule fumarate in step seven, transforming it to malate, another four-carbon molecule.
8. Oxidation of malate regenerates oxaloacetate, the beginning four-carbon molecule, in the last phase of the citric acid cycle. In the process, another molecule of NAD+ is reduced to NADH.

TCA Cycle End Products

The following are the end products of a Citric Acid cycle:

• Two carbon dioxide molecules
• Three NADH molecules, three hydrogen ions, and one FADH2 molecule
• One ATP or GTP molecule is produced.

• Conclusion

  Two carbon molecules enter the route from acetyl CoA, and two carbon dioxide molecules are emitted. Three NADH molecules, three hydrogen ions, one FADH2 molecule, and one ATP molecule are created. It’s worth noting that one molecule of glucose produces two molecules of Acetyl CoA. As a result, the total final product is doubled.