Question

consider one glucose unit in glycogen. what is the overall or net reaction for the conversion of this unit into 2 pyruvate, starting with phosphorolysis of the glucose unit?

Answer 1

This cycle is known as Glycolysis

Glycolysis is the 10 step process, which occurs in cytoplasm of cell and  is conversion of glucose to pyruvate.

There are several steps and enzymes that is required in glycolysis pathway.

STEP 1: PHOSPHORYLATION

This is irreversible reaction.

Here glucose is phosphorylated to glucose 6 phosphate with the help of enzyme hexokinase and 1 ATP is utilized.

STEP 2 : ISOMERISATION

The isomerization of Glucose-6-phosphate to Fructose-6-phosphate, done with the help of enzyme phosphoglucoisomerase.

STEP 3 : SECOND PHOSPHORYLATION

Fructose-1,6-bisphosphate is phosphorylated to Fructose 1,6 bisphosphate  which is catalyzed by  phosphofructokinase and cost another ATP.

STEP 4: BREAKDOWN

The fructose-1,6 bisphosphate  is breaken down too produce two 3carbon molecules -  Glyceraldehyde-3-phosphate, or GADP, and a molecule of Dihydroxyacetone phosphate or DHAP.

The reaction is catalyzed by aldolase.

STEP 5 : CONVERSION OF DHAP INTO GADP

DHAP is oxidized to form GADP.

The reaction is catalyzed by triose phosphate isomerase enzyme.

STEP 6: OXIDATION

Here 2 mol. of GADP are oxidized.The GDAP is converted to 1,3 bisphosphoglycerate with the help of  glyceraldehyde phosphate dehydrogenase. This requires NAD+ and a free phosphate.

STEP 7: DEPHOSPHORYLATION

First substrate level phosphorylation ( addition of phosphate to ADP to give ATP )

1,3 bisphosphoglycerate with the help of Phosphoglycerate kinase become 3-phosphoglycerate and will produce 1 ATP.

STEP 8: PHOSPHATE TRANSFER

The phosphate ester linkage in 3 phosphoglycerate is moved from 3 C to 2 , because of low free energy to form 2 phosphoglycerate  with the help of phosphoglycerate mutase .

STEP 9: DEHYDRATION

2 phopshoglycerate is dehydrated by enolase to form Phosphoenolpyruvate ( PEP)

This is reversible reaction.

STEP 10: SECOND DEPHOSPHORYLATION

2 substrate level phosphorylation which gives out ATP.

Non - oxidative phosphorylation.

Here Phosphoenolpyruvate ( PEP) is converted to last product of glycolysis pyruvate releasing ATP by pyruvate kinase.

The first five step is production of GADP, And usage of ATP and the next five steps are the formation of ATP and pyruvate. The net formation of ATP is 2 mol. of ATP and 2 mol. of NADH.  This pyruvate then move to the TCA cycle.

To know more about glycolysis -

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