Krebs Cycle Or Citric Acid Cycle: Biochemistry, Metabolism, Enzymes

What Is The Krebs Cycle?

The Krebs cycle, also identified with the terms citric acid cycle and tricarboxylic acid (TCA) cycle, is this important fundamental metabolic pathway that carries much significance in cellular respiration. After glycolysis, the second step regarding aerobic respiration is the Krebs cycle. The cycle takes place in the mitochondrial matrix of all eukaryotic cells. So this is the cycle that converts carbohydrates, fats, and proteins into carbon dioxide, water, and energy.

Krebs Cycle As A Stage Of Cellular Respiration

The most specified stage of cellular respiration is the Krebs cycle, and in such a cycle, all the specified potential chemical energy in glucose and other organics is converted to adenosine triphosphate. As a rule, cellular respiration occurs in three emphasized stages:

• Glycolysis: This is a process in which glucose is broken into two pyruvates to give a small product of AT1 and NADH.

• Krebs Cycle: Pyruvate gets decarboxylated and enters the mitochondria and thus is oxidized in the Krebs cycle. The result of this oxidation reaction is three molecules, including NADH, FADH2, and GTP/ATP.

• Electron Transport Chain and Oxidative Phosphorylation: This energy from NADH and FADH2 provides a series of oxidation-reduction reactions that follow the removal of the protons and electrons; the protons and high-energy electrons extracted in this process are used to pump the electrons in the electron transport chain generating a transmembrane electrochemical gradient, which powers some of the energy thus released.

• Citrate is formed by the condensation reaction of acetyl-CoA with oxaloacetate. Citrate is converted to the isomer, isocitrate. Isocitrate reacts with NAD+ to form α-ketoglutarate and NADH. At the same time, a carboxyl group becomes decarboxylated in the oxidative decarboxylation reaction. α-Ketoglutarate reacts with NAD+ forming NADH and succinyl-CoA. Succinyl-CoA reacts with GDP and inorganic phosphate to form succinate and GTP. GTP is used by the cell to make.

• Hydratation: Fumarate is hydrated to malate.

• Final Oxidation: Malate is oxidised to oxaloacetate producing another NADH.

Overall Summary Of Kreb's Cycle

Krebs cycle can, therefore be summarised as:

• Acetyl-CoA joins the cycle through combing with oxaloacetate. Then, citrate is formed.

• The cycle follows our line of oxidation and decarboxylation.

• It produces NADH and FADH2, where NADH and FADH2 are utilized in the ATP synthesis in the electron transport chain.

• It generates carbon dioxide as an excretory product.

• Towards the end of the cycle, oxaloacetate is regenerated, and it reloads the same cycle once again.

Krebs Cycle Equation

The overall Krebs cycle can be appropriately represented in the following equation:

Importance Of Krebs Cycle

1. Energy Production: The most important point regarding the significance of the Krebs cycle, is the line of production for the high-energy electron carriers NADH and FADH2, which, in turn, produce ATP through the electron transport chain.

2. Carbon Dioxide Production: The cycle is a producer of carbon dioxide, forming a waste product that can be excreted from the body after respiration.

3. Biosynthesis: Various intermediates of the Krebs cycle serve as a source or precursor of the synthesis of important biomolecules like amino acids and nucleotides.

Regulation Of The Krebs Cycle

Tightly regulated, the Krebs cycle ensures that the production of energy is accessible in amounts required for metabolic needs. Easily identified control enzymes of the cycle include:

1. Citrate Synthase: Controls entry of acetyl-CoA into the cycle.

2. Isocitrate Dehydrogenase: The activity of this enzyme, for the conversion of isocitrate to alpha-ketoglutarate, is controlled by levels of NADH and ATP.

3. Alpha-Ketoglutarate Dehydrogenase: Logic identical to that of isocitrate dehydrogenase, for a proper balance of energy production about the availability of the substrate.

Relationship Between Glycolysis And The Krebs Cycle

The Krebs cycle is directly connected to glycolysis through pyruvate transformation into acetyl-CoA. After the reception of the end product of glycolysis within the cytoplasm, pyruvate diffused in the mitochondria undergoes oxidative decarboxylation, forming acetyl-CoA and NADH. The acetyl-CoA formed is assimilated into the Krebs cycle and is completely oxidized with the release of energy.

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