Master Glycolysis

Step 1: Glucose + ATP → ? Which enzyme?

Hexokinase (glucokinase in liver): glucose + ATP → glucose 6-phosphate + ADP. Irreversible.

Step 2: Glucose 6-phosphate ⇌ fructose 6-phosphate. Which enzyme?

Phosphohexose isomerase (a.k.a. phosphoglucose isomerase): aldose → ketose

Step 3: Fructose 6-phosphate + ATP → fructose 1,6-bisphosphate + ADP. Which enzyme?

Phosphofructokinase-1 (PFK-1). Irreversible, main control point.

Step 4: Fructose 1,6-bisphosphate ⇌ two 3-carbon products. Which enzyme?

Aldolase: gives dihydroxyacetone phosphate (DHAP) + glyceraldehyde 3-phosphate (G3P)

Step 5: DHAP ⇌ glyceraldehyde 3-phosphate. Which enzyme?

Triose phosphate isomerase (TPI)

Step 6: Glyceraldehyde 3-phosphate + NAD⁺ + Pi ⇌ 1,3-bisphosphoglycerate + NADH. Which enzyme?

Glyceraldehyde 3-phosphate dehydrogenase (GAPDH)

Step 7: 1,3-Bisphosphoglycerate + ADP ⇌ 3-phosphoglycerate + ATP. Which enzyme?

Phosphoglycerate kinase (substrate-level phosphorylation)

Step 8: 3-Phosphoglycerate ⇌ 2-phosphoglycerate. Which enzyme?

Phosphoglycerate mutase

Step 9: 2-Phosphoglycerate ⇌ phosphoenolpyruvate + H2O. Which enzyme?

Enolase (dehydration)

Step 10: Phosphoenolpyruvate + ADP → pyruvate + ATP. Which enzyme?

Pyruvate kinase. Irreversible, substrate-level phosphorylation.

What does hexokinase do?

Glucose + ATP → glucose 6-phosphate + ADP (uses ATP, irreversible)

What does phosphohexose isomerase do?

Glucose 6-phosphate ⇌ fructose 6-phosphate (no cofactor)

What does PFK-1 do?

Fructose 6-phosphate + ATP → fructose 1,6-bisphosphate + ADP (uses ATP, irreversible, main control point)

What does aldolase do?

Fructose 1,6-bisphosphate ⇌ DHAP + glyceraldehyde 3-phosphate (C–C cleavage, no cofactor)

What does triose phosphate isomerase do?

DHAP ⇌ glyceraldehyde 3-phosphate (no cofactor)

What does GAPDH do?

Glyceraldehyde 3-phosphate + NAD⁺ + Pi ⇌ 1,3-bisphosphoglycerate + NADH + H⁺ (uses NAD⁺, makes the first high-energy phosphate compound)

What does phosphoglycerate kinase do?

1,3-Bisphosphoglycerate + ADP ⇌ 3-phosphoglycerate + ATP (makes ATP, substrate-level phosphorylation)

What does phosphoglycerate mutase do?

3-Phosphoglycerate ⇌ 2-phosphoglycerate (moves the phosphate from C3 to C2)

What does enolase do?

2-Phosphoglycerate ⇌ phosphoenolpyruvate + H2O (dehydration, creates the high-energy enol phosphate)

What does pyruvate kinase do?

Phosphoenolpyruvate + ADP → pyruvate + ATP (makes ATP, substrate-level phosphorylation, irreversible)

Structural change: glucose → glucose 6-phosphate

Phosphate added on C6

Structural change: glucose 6-phosphate → fructose 6-phosphate

Aldose → ketose: carbonyl moves from C1 to C2, ring goes from 6- to 5-membered

Structural change: fructose 6-phosphate → fructose 1,6-bisphosphate

Second phosphate added on C1

Structural change: fructose 1,6-bisphosphate → DHAP + G3P

Aldolase cleaves the C3–C4 bond, giving two 3-carbon pieces

Structural change: DHAP → glyceraldehyde 3-phosphate

Ketose → aldose: carbonyl moves from C2 to C1

Structural change: glyceraldehyde 3-phosphate → 1,3-bisphosphoglycerate

Aldehyde oxidized to an acyl phosphate (high-energy bond), NAD⁺ → NADH

Structural change: 1,3-bisphosphoglycerate → 3-phosphoglycerate

Acyl phosphate transferred to ADP, leaving a carboxylate

Structural change: 3-phosphoglycerate → 2-phosphoglycerate

Phosphate shifts from C3 to C2

Structural change: 2-phosphoglycerate → phosphoenolpyruvate

Water removed, giving a C2=C3 double bond (enol phosphate)

Structural change: phosphoenolpyruvate → pyruvate

Phosphate transferred to ADP, enol tautomerizes to the ketone

Intermediate after glucose?

Glucose 6-phosphate

Intermediate after glucose 6-phosphate?

Fructose 6-phosphate

Intermediate after fructose 6-phosphate?

Fructose 1,6-bisphosphate

Intermediate after fructose 1,6-bisphosphate?

DHAP + glyceraldehyde 3-phosphate

Intermediate after DHAP?

Glyceraldehyde 3-phosphate

Intermediate after glyceraldehyde 3-phosphate?

1,3-Bisphosphoglycerate

Intermediate after 1,3-bisphosphoglycerate?

3-Phosphoglycerate

Intermediate after 3-phosphoglycerate?

2-Phosphoglycerate

Intermediate after 2-phosphoglycerate?

Phosphoenolpyruvate (PEP)

Intermediate after phosphoenolpyruvate?

Pyruvate

Which 3 glycolysis steps are irreversible in cells?

Hexokinase (step 1), PFK-1 (step 3), pyruvate kinase (step 10)

Which glycolysis step uses NAD⁺?

Step 6, GAPDH

Which 2 steps are substrate-level phosphorylation?

Step 7 (phosphoglycerate kinase) and step 10 (pyruvate kinase)

Which steps use ATP and which make ATP?

Steps 1 and 3 use 2 ATP total. Steps 7 and 10 make ATP.

Net yield of glycolysis per glucose?

2 pyruvate, 2 ATP net (4 made, 2 spent), 2 NADH

Why do steps 6–10 happen twice per glucose?

Aldolase gives two 3-carbon pieces and TPI converts DHAP to G3P, so both halves go through the payoff phase