GLYCOLYSIS ( WITH EASY TRICKS )

Mechanism of Aerobic Respiration:

Aerobic respiration is a catabolic process which involves complete oxidative breakdown of organic food (especially glucose) into carbon dioxide and water with release of great deal of energy in the form of ATPs. It is predominant respiratory pathway in most of the organisms.

Aerobic respiration is completed in four phases: glycolysis, oxidation of pyruvates, Krebs cycle and respiratory electron transport chain.

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Glycolysis:

Glycolysis is the process of breakdown of glucose or similar hexose sugar into two molecules of pyruvates through a series of enzymatic reactions releasing some energy (as ATP) and reduced coenzymes (as NADH). It occurs in the cytoplasm. 

It is completed in two phases ie, preparatory phase and oxidative phase. Preparatory phase is an investment phase in which two ATPs are consumed. Its end products are two molecules of G3P. 

On the other hand oxidative phase is pay off phase in which not only ATPs are produced through substrate level phosphorylation but it also produces NADH which upon further oxidation in respiratory electron transport chain yields more ATPs. 

The whole glycolysis pathway takes place in the following sub steps.

1. Phosphorylation:

When glucose reacts with ATP, a phosphate group from ATP is transferred to glucose. In this way glucose is phosphorylated to glucose-6-phosphate. MDCA

2. Isomerization:

Glucose-6-phosphate is changed to its isomer fructose-6-phosphate..

 3. Phosphorylation:

When fructose-6 phosphate reacts with another ATP, is phosphorylated to Fructose-1, 6-bisphosphate.

4. Splitting:

Now fructose-1, 6-bisphosphate splits up to form one molecule each of 3 carbon compounds, glyceraldehyde 3 phosphate (G3P) and dihydroxyacetone 3 phosphate.

5. Isomerization:

The dihydroxyacetone 3 phosphate is ultimately changed into its isomer, the glyceraldehyde 3-phosphate (G3P). In this way preparatory phase is completed. Next phase I glycolysis is proceeded by two molecules of G3P, therefore, the remaining reactions occur twice.

6. Dehydrogenation and Phosphorylation:

NADH and accepts inorganic phosphate (Pi) to form 1, 3-bisphosphoglycerate.

7. Formation of ATP:

The direct synthesis of ATP from organic phosphorylated substrate is called substrate level phosphorylation. In this step a molecule of ATP is formed from 1, 3 bisphosphoglycerate which is changed into 3-phosphoglycerate.

8. Isomerization:

In this step position of phosphate group is changed from C3 to C2 of Glycolysis is also called EMP pathway undergoes dehydration and is converted into German scientists Embden, Meyerhof phosphoenol pyruvate (PEP). and Parnas. phosphoglycerate to form 2-phosphoglycerate.

 9. Dehydration:

In this step, 2-phosphoglycerate because it was discovered by three.

10. Formation of ATP:

Again a molecule of ATP is produced by substrate level phosphorylation when phosphoenol pyruvate loses phosphate group which is taken up by the ADP to form ATP in the presence of an enzyme (pyruvate kinase). The phosphoenol pyruvate is finally converted into pyruvate.

 Oxidation of Pyruvate:

Pyruvates are produced in cytosol. Because pyruvate is a charged molecule, it must enter the mitochondrion via active transport with the help of the transport protein.

The oxidation of pyruvate takes place three steps. First, it undergoes C=0 in decarboxylation in which a molecule of CO₂ is removed from pyruvate to form acetaldehyde. Then NAD NAD' removes hydrogen from acetaldehyde. 

As a result of this oxidation/ dehydrogenation a fragment acetyl and NADH are produced. Finally, acetyl group is combined with coenzyme-A to form acetyl CoA.