Glycolysis Steps

Step 1: Phosphorylation

Investment/Payoff Step or Neither: Investment

Enzyme: Hexokinase

Substrate: Glucose

Product: Glucose-6-P

What it Does: “Activation” of glucose for glycolysis, traps it in the cell

Other: Coupled to ATP Hydrolysis, essentially irreversible

Step 2: Isomerization

Investment/Payoff Step or Neither: Neither

Enzyme: Phosphoglucoisomerase

Substrate: Glucose-6-P

Product: Fructose-6-P

What it does: Converts an aldose to a ketose

Step 3: Phosphorylation

Investment/Payoff Step or Neither: Investment

Enzyme: Phosphofructokinase-1

Substrate: Fructose-6-P

Product: Fructose-1,6-BP

What it does: Phosphorylates the Fructose-6-P

Other: Coupled with ATP hydrolysis, essentially irreversible; First committed step

Step 4: Cleavage

Investment/Payoff Step or Neither: Neither

Enzyme: Aldolase

Substrate: Fructose-1,6-BP

Product: Glyceraldehyde-3-P and Dihydroxyacetone-P

What it does: Reverse aldol condensation - yields an aldose and ketose

Step 5: Isomerization

Investment/Payoff Step or Neither: Neither

Enzyme: Triose Phosphate Isomerase (TPI)

Substrate: Dihydroxyacetone-P

Product: Glyceraldehyde-3-P

What it does: C1-3 is now chemically the same as C6-4

Step 6: Oxidation

Investment/Payoff Step or Neither: Payoff (with NADH)

Enzyme: Glyceraldehyde 3-phosphate dehydrogenase (GAPDH)

Substrate: Glyceraldehyde-3-P

Product: 1,3-Biphosphoglycerate

What it does: Oxidation and substrate level phosphorylation

Other: There is a lot of stored energy in the new phosphoanhydride bond; coupled with step 7

Step 7: Dephosphorylation

Investment/Payoff Step or Neither: Payoff (with ATP)

Enzyme: Phosphoglycerate kinase

Substrate: 1,3-Bisphosphoglycerate

Product: 3-Phosphoglycerate

What it does: Makes a more stable product

Other: Coupled with step 6

Step 8: Isomerization

Investment/Payoff Step or Neither: Neither

Enzyme: Phosphoglycerate mutase (PGM)

Substrate: 3-Phosphoglycerate

Product: 2-Phosphoglyerate

What it does: Move the functional group from the 3 position to the 2 position to set up the remaining reactions

Step 9: Dehydration

Investment/Payoff Step or Neither: Neither

Enzyme: Enolase

Substrate: 2-Phosphoglycerate

Product: Phosphoenolpyruvate (PEP)

What it does: Continuing to set up for energy harvest

Other: PEP has 3 times the phosphoryl potential as 2-PG

Step 10: Dephosphorylation

Investment/Payoff Step or Neither: Payoff (with ATP)

Enzyme: Pyruvate kinase (PK)

Substrate: Phosphoenolpyruvate

Product: Pyruvate

What it does: Dephosphorylates the substrate

Other: Tautomerization from enol to more stable keto form is what makes this reaction so favorable