Glycolysis

 

Glycolysis

    Glycolysis is the breakdown of glucose molecules into pyruvate.

    Glucose can produce many things like polysaccharides, glycogen starch glucose, ribose-5-phosphate and pyruvate but only the conversion of glucose into pyruvate is known as glycolysis.

 

The process of glycolysis occur in different ways like;

·         It carried out in nearly every living cell specially in the cytosol of eukaryotic cell.

·         It release energy which is stored in covalent bond.

·         It undergoes in stepwise degradation in glucose and other simple sugars.

 

 

Overview of Glycolysis:  

 

Process of glycolysis occur in two phases.

·         Phase 1 is Energy Investment Phase

·         Phase 2 is Energy payoff Phase

 

    These two phases of glycolysis occur in ten (10) different reaction. Reaction 1-5 are energy investment phase and reaction 6-10 are energy payoff phase.

 

Glycolysis 

 

Phase-1:     Energy Investment Phase

STEP-1:     PHOSPHORYLATION:

 

·           Glycolysis take place in cytosol of cell.

·           Glucose enter into the glycolysis pathway by conversion  to glucose-6-pathway.

·           Initially there is energy input corresponding to cleavage of two ~P bonds of ATP.

·           Kinase is the enzyme that catalyzes the phosphorylation of molecules using ATP.

 

 

 

Step-1:      Phosphorylation

Phosphorylation 

 

STEP-2:     ISOMERIZATION:

    “Phosphohexose Isomerase” is an enzyme that catalyze the transformation of compound in their positional isomers. In the case of sugar this usually involves the interconversion of an aldose sugar into ketose sugar or vice versa.

 

 

 

Step-2:      Isomerization:

Isomerization

STEP-3:     PHOSPHORYLATION:

    Phosphofructokinase is the enzyme that catalyze the transformation of fructose-6-phosphate into fructose-1,6-bisphosphate. By the phosphorylation, the ATP molecule will convert into the ADP molecule.

PHOSPHORYLATION

 

 

 

STEP-4:     CLEAVAGE:

·           In the cleavage step, fructose-1,6-bisphosphate will convert into the Dehydroxyacetone phosphate and glyceraldehyde-3-phosphate.

·        This reaction is an aldose cleavage reaction, the reverse of an aldose condensation.

·        Carbon atoms are renumbered in the product of Aldolase.

·       

      STEP-5:     ISOMERIZATION:

·             The enzyme “Trios phosphate isomerase” catalyzes Dehydroxyacetone phosphate into Glyceraldehyde-3-phosphate.

·         

     Phase-2:     Energy Payoff Phase

·        

       STEP-6:     OXIDATION:

    Glyceraldehyde-3-phosphate and NAD⁺ and 1-phosphate molecule will be convert into 1,3-bisphosphoglycerate and NADH And one proton molecule by the action of enzyme “Glyceraldehyde-3-phosphate dehydrogenase”.

 

  STEP-7:  SUBSTRATE LEVEL PHOSPHORYLATION:

·           The enzyme “Phosphoglycerate Kinase” catalyzes the 1,3-bisphosphoglycerate and ADP into 3-phosphoglycerate and ATP.

·           This phosphate transfer is irreversible.

·        

       STEP-8:  SHIFT OF PHOSPHORYL GROUP:

·           The enzyme “Phosphoglycerate Mutase” catalyzes the 3-phosphoglycerate into 2-phosphoglycerate.

·        Mutase is actually an enzyme that catalyze the transposition of functional group, such as phosphate, sulphate etc.

 

   STEP-9:     DEHYDRATION:

·           The enzyme “Enolase” catalyzes the 2-phosphoglycerate into phosphophenolpyruvate and water molecule.

·       This dehydration reaction is Mg⁺ dependent.

·        

       STEP-10: SUBSTRATE LEVEL PHOSPHORYLATION:

·             The enzyme “Pyruvate Kinase” catalyzes the phosphophenolpyruvate and ADP into Pyruvate and ATP.