Question

Explain : Kreb's cycle​

Answer 1

Explanation:

The citric acid cycle – also known as the TCA cycle or the Krebs cycle – is a series of chemical reactions used by all aerobic organisms to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins

Answer 2

                               Kreb's Cycle

It is a cycle involving a series of reactions followed by link reaction in the aerobically res-pirating organisms.

Occurrence :

• Prokaryotic Organisms - Cytosol
• Eukaryotic Organisms - Mitochondrial matrix

The Kreb's cycle is called as citric acid cycle or tri-carboxylic acid cycle.

In order to under the complete cycle, now refer to the series of 10 steps :

1. Oxalic Acetic Acid (OAA) - [6c]: This acid undergoes condensation and marks the beginning of the Kreb's cycle. It involves addition of H₂O, Acetyl CoA and engyme citrate synthase to form citrate.
2. Citrate [6c] : It is the first product of Kreb's cycle. Water is released after its formation as dehydration takes place. Enzymes aconitase activates to further continue the reaction.
3. Cisaconitate [6c] : Engyme aconitase again acts on this product along with its hydration i.e. H₂O is added again.
4. Isocitrate [6c] : After its formation, isocitrate dehydrogenase acts along with oxidation of NAD⁺ to form NADH + H⁺.
5. Oxalosuccinate [6c] : Its formation marks the beginning of decarboxylation and is brought about by enzyme oxalosuccinate decarboxylase.
6. α-Ketoglutarate [5c] : Loss of carbon in oxalosuccinate step marks the reduce in the number of carbon to 5. Here, oxidative decarboxlation takes place along with dehydrogenation of NAD⁺ to NADH + H⁺ with the help of the enzyme α-ketoglutarate dehydrogenase. Along with it, CoA is added for further continuation.
7. Succinyl CoA [4c] : Here, GDP along with Pi becomes GTP. Moreover, ADP +Pi becomes ATP marking the release of energy. This substrate level phosphorylation is brought about by the enzyme succinate thiokinase. Also, CoA is released in the process.
8. Succinate [4c] : Flavin adenine dinucleotide gets reduced to flavin adenine dinucleotide hydrogen as oxidation takes place. This is brought about by succinate dehydrogenase.
9. Fumarate [4c] : This is end product of succinate step. After its formation, enzyme fumarase activates to form malate. Moreover, along with it, its hydration also takes place.
10. Malate [4c ] : This is the end product of Kreb's cycle. After its formation, the cycle repeats again. Enzyme malate dehydrogenase reduces NAD⁺ to NADH + H⁺.

Extra Information :

Continuity of Kreb's cycle requires :

• replenishment ( regeneration ) of oxalo acetic acid ( OAA ).
• oxidation of NADH and FADH / availability of NAD⁺ and FAD.