Glycolysis

Stage 1

Investment phase (steps 1-5)

Stage 2

“payoff” phase (steps 6-10)

Yield of glycolysis

net 2 ATP

2 NADH

2 pyruvate

Step 1

phosphorylation of glucose to glucose-6-phosphate (G6P)

What enzyme phosphorylates glucose (step 1)?

hexokinase (Mg is a cofactor)

Which steps require an input of ATP?

Steps 1 and 3

Step 2

Isomerization of glucose-6-phosphate (G6P) to fructose-6-phosphate (F6P)

What enzyme isomerizes G6P to F6P?

phosphoglucose isomerase (PGI)

Step 3

phosphorylation of fructose-6-phosphate (F6P) to fructose-1,6-bisphosphate (FBP)

What enzyme phosphorylates F6P?

phosphofructokinase (Mg is a cofactor)

Step 4

cleavage of fructose-1,6-bisphosphate (FBP) to glyceraldehyde-3-phosphate (GAP/G3P) and dihydroxyacetone phosphate (DHAP)

What enzyme cleaves FBP into GAP and DHAP?

aldolase

Step 5

dihydroxyacetone phosphate (DHAP) converted to glyceraldehyde-3-phosphate (GAP/G3P)

What enzyme converts DHAP to GAP?

triose phosphate isomerase

At the end of Step 5, what has been created?

2 GAP/G3P

Step 6

phosphorylation of glyceraldehyde-3-phosphate (GAP/G3P) to 1,3-bisphosphoglycerate (1,3-BPG)

What enzymes phosphorylates GAP?

glyceraldehyde-3-phosphate dehydrogenase (GAPDH)

What kind of reaction is Step 6? What else is required/made?

oxidation-reduction reaction; NAD+ is required and NADH is made

Step 7

Dephosphorylation of 1,3-bisphosphoglycerate (1,3-BPG) to produce 3-phosphoglycerate (3PG) and ATP

What two steps make ATP?

Steps 7 and 10

What enzyme dephosphorylates 1,3-BPG?

phosphoglycerate kinase (PGK); ADP is needed and Mg is a cofactor

Step 8

3-phosphoglycerate (3PG) is rearranged to 2-phosphoglycerate (2PG)

What enzyme rearranges 3PG to 2PG?

phosphoglycerate mutase (PGM)

Step 9

elimination of H2O from 2-phosphoglycerate (2PG) to produce phosphoenolpyruvate (PEP)

What enzyme eliminates water from 2PG?

enolase

Step 10

dephosphorylation of phosphoenolpyruvate (PEP) to form ATP and pyruvate

What enzyme dephosphorylates PEP?

pyruvate kinase (ADP is needed)

Which steps of glycolysis are reversible?

2, 4-9 — these steps are common to the gluconeogenesis pathway

Which steps of glycolysis are irreversible?

1,3,10

Which steps of glycolysis are regulated?

1,3,10 (irreversible!!)