Question

(Make your answer worth 100Pts) You are an electron in a glucose molecule. You are digested by a human and through the energy metabolism pathways your ultimate fate is to end up as an electron in a water molecule. Take me on the journey. Include every reaction you participate in (reactants, enzymes, co-enzymes, carrier proteins). There are multiple ways you can do this. If you are smart, you can make this an relatively easy journey.

How do I incorporate the pentode phosphate pathway/ shunt into this?

Answer 1

The pathway involved in metabolism of glucose is called Glycolysis, and consists of sequential steps that ultimately produce Pyruvate , ATP , H+ and NADH. The steps are as follows :

1) The conversion of Glucose to Glucose-6-phosphate takes place by phosphorylation of glucose through Hexokinase enzyme, and ATP is consumed. The cofactor for Hexokinase is Mg2+ ion.

Glucose + ATP ---> Glucose-6-phosphate + ADP + H+

2) Glucose-6-phosphate is then rearranged to Fructose-6-phosphate , and it is mediated by Phosphoglucose Isomerase enzyme.

Glucose-6-phosphate ---> Fructose-6-phosphate

3) After this, Fructose-6-phosphate is converted into Fructose 1,6-bisphosphate by addition of another phosphate group and consuming ATP. The enzyme involved in this conversion is Phosphofructokinase, which is a transferase enzyme and its cofactor is Mg2+ ion again.

Fructose-6-phosphate + ATP ---> Fructose-1,6-bisphosphate + ADP + H+

4) Since Fructose 1,6-bisphosphate is a very unstable molecule due to presence of two phosphate groups, so it splits into two 2 triose sugars. Those two molecules are Dihydroxyacetone phosphate and Glyceraldehyde-3-phosphate. This breakdown is mediated by a lyase enzyme called fructose bisphosphate aldolase. Dihydroxyacetone phosphate interconverts into Glyceraldehyde-3-phosphate by an isomerase enzyme called Triosephosphate Isomerase. The ultimate product in this step will be Glyceraldehyde-3-phosphate.

Fructose 1,6-bisphosphate ---> Dihydroxyacetone phosphate + Glyceraldehyde-3-phosphate

5) Now, Glyceraldehyde-3-phosphate is oxidised into 1,3-bisphosphoglycerate by an oxidoreductase enzyme called Glyceraldehyde phosphate dehydrogenase. Here, hydrogen reduces two NAD+ molecules to yield NADH + H+ for each triose.

Glyceraldehyde-3-phosphate + Pi + NAD+ ---> 1,3-Bisphosphoglycerate + NADH + H+

6) After this, 1,3-bisphosphoglycerate is converted into 3-phosphoglycerate by removal of Phosphate group. Phosphoglycerate Kinase enzyme mediates this reaction, and the released phosphate group converts ADP into ATP. This ATP is then released. The cofactor is Mg2+ ion, which actually binds to ADP & ATP, forming ADPMg- and ATPMg2- respectively.

1,3-Bisphosphoglycerate + ADP ---> 3-Phosphoglycerate + ATP

7) Next step is the rearrangement of 3-phosphoglycerate into 2-phosphoglycerate. This isomerisation is mediated by Phosphoglyceromutase enzyme.

3-Phosphoglycerate ---> 2-Phosphoglycerate

8) Now, this 2-phosphoglycerate is converted into phosphoenolpyruvate by a lyase enzyme called Enolase. Water molecule is also released here. Two Mg2+ ions act as cofactor here, one of them binds to carboxylate group of 2-phosphoglycerate and the other one is involved in dehydration.

2-Phosphoglycerate ---> Phosphoenolpyruvate + H2O

9) The final step is the conversion of phosphoenolpyruvate into Pyruvate along with the release of another ATP molecule. A transferase enzyme called Pyruvate Kinase mediates this reaction. The cofactor is Mg2+ ion again.

Phosphoenolpyruvate + ADP + H+ ---> Pyruvate + ATP

So the above mentioned steps are involved in the metabolism of Glucose through Glycolysis. The overall reaction of Glycolysis is :

D-Glucose + 2 [NAD+] + 2 [ADP] + 2 [Pi] --------> 2 [Pyruvate] + 2 [NADH] + 2 [H+] + 2 [ATP] + 2 [H2O]

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