First investment — trapping glucose inside the cell
⬡
Glucose
C₆H₁₂O₆
6 carbons0 phosphates
🔄
Hexokinase
−1 ATP
⬡
Glucose-6-Phosphate
G6P
6 carbons+1 phosphate 🔒
💸 Energy Investment
ATP → ADP + Pᵢ | Total spent so far: 1 ATP
🎮 Game Analogy
Theme park ticket stamp! You pay $1 (ATP) to get your ticket stamped (phosphate). The stamp means you can't leave — glucose is permanently trapped inside the cell!
🎯 Key Points
✅ Phosphate = molecular lock (too big/charged to exit)
✅ Enzyme: Hexokinase — rate-limiting step
✅ Investment: 1 ATP spent
✅ Irreversible under cellular conditions
📝 Challenge Questions
QUESTION 1 OF 3
Why does the cell "spend" ATP at the very start of glycolysis?
Think about what a phosphate group does to glucose's ability to cross the cell membrane...
QUESTION 2 OF 3
What would happen if hexokinase was completely missing from the cell?
Stage 1 is the entry gate. If the gate is missing, can anything pass through to Stage 2?
QUESTION 3 OF 3
The phosphate group added to glucose acts most like...
The function is to KEEP something in one place. Which analogy does that?
🎉 Stage 1 Complete! Running XP: 0
STAGE 2 OF 10 · INVESTMENT PHASE
Isomerization Shuffle 🔄
Same atoms, new arrangement — preparing for the big split!
⬡
Glucose-6-Phosphate
G6P · Aldose
6-ringC=O at C1
🎲
PGI Isomerase
No ATP used
⬠
Fructose-6-Phosphate
F6P · Ketose
5+1 ringC=O moved to C2
🎮 Game Analogy
Rearranging furniture! Same room, same pieces — just moved to make room for dancing. The carbonyl group shifts from C1 to C2, which is essential for the upcoming split.
🎯 Key Points
✅ Same atoms, different structure (isomers)
✅ Enzyme: Phosphoglucose Isomerase
✅ Carbonyl group: C1 → C2
✅ Only the fructose form can be split symmetrically in Stage 4
📝 Challenge Questions
QUESTION 1 OF 3
Why is isomerization necessary before the molecule can be split?
Think ahead to Stage 4: which molecular shape allows aldolase to make a clean, equal split?
QUESTION 2 OF 3
What does "isomerization" mean at the molecular level?
"Iso" means equal or same. What stays exactly the same in this reaction?
QUESTION 3 OF 3
What is the key structural difference between G6P and F6P?
Look at the molecule cards above. What tag changed between G6P and F6P?
🎉 Stage 2 Complete! Running XP: 0
STAGE 3 OF 10 · COMMITMENT STEP ⚠️
The Power Boost ⚡
Second ATP investment — the point of no return!
⬠
Fructose-6-Phosphate
F6P · 1 phosphate
P at C6 only
⚡
PFK-1 ⚠️
−1 ATP
⬠
Fructose-1,6-Bisphosphate
F1,6BP · 2 phosphates
+P at C1P at C6
💸 Total Invested: 2 ATP — No Going Back!
PFK-1 is inhibited by high ATP — the cell's built-in energy thermostat. When energy is abundant, glycolysis slows. When energy is scarce, it speeds up. Brilliant regulation!
🎮 Game Analogy
Non-refundable upgrade purchase! You spend gold (2nd ATP) to activate "Mega Weapon" before the boss fight. PFK-1 is the game shopkeeper — once you buy, there's absolutely no refund. You're committed!
🎯 Key Points
⚠️ Irreversible — once F1,6BP forms, no going back
⚠️ Rate-limiting — the most tightly controlled step
✅ Enzyme: Phosphofructokinase-1 (PFK-1)
✅ Total investment: 2 ATP spent
📝 Challenge Questions
QUESTION 1 OF 3
Why is the PFK-1 reaction called the "Commitment Step"?
Think "non-refundable." What makes a purchase truly non-refundable?
QUESTION 2 OF 3
What makes PFK-1 the most important regulatory enzyme in glycolysis?
If the cell already has lots of ATP, should it make more? How does it signal "enough"?
QUESTION 3 OF 3
If PFK-1 was completely blocked by a drug, what happens to glycolysis?
PFK-1 controls the "commitment." Block the commitment and what must happen downstream?
🎉 Stage 3 Complete! Running XP: 0
STAGE 4 OF 10 · THE SPLIT
The Great Split 💥
One 6-carbon molecule becomes two 3-carbon molecules!
⬠
Fructose-1,6-Bisphosphate
6C · 2 phosphates
C3–C4 bond
⚔️
Aldolase
No energy change
△
G3P
3 carbons
Continues! ✅
+
△
DHAP
3 carbons
→ G3P in Stage 5
🎮 Game Analogy
Snapping a 6-piece chocolate bar! You break it exactly in half → two 3-piece halves. Same total chocolate, just separated. No energy gained or lost — pure cleavage!
🎯 Key Points
✅ Bond broken: between C3 and C4 (exact center)
✅ Products: G3P (aldehyde) + DHAP (ketone)
✅ DHAP converts to G3P in Stage 5
✅ No energy change — cleavage only
📝 Challenge Questions
QUESTION 1 OF 3
What does aldolase do in this reaction?
The stage is called "The Great SPLIT" — that's exactly what aldolase does!
QUESTION 2 OF 3
Which specific carbon-carbon bond is cleaved by aldolase?
To split a 6-carbon chain into TWO EQUAL 3-carbon halves, which bond is right in the middle?
QUESTION 3 OF 3
What is the energy outcome of the aldolase reaction?
Breaking a candy bar doesn't give you more chocolate. The same applies here!
🎉 Stage 4 Complete! Running XP: 0
STAGE 5 OF 10 · TWIN CONVERSION
Two-for-One Deal 🔀
DHAP → G3P: Everything from here happens TWICE!
△
DHAP
Ketone · dead end
⛔ Can't continue
🔀
TPI Isomerase
Fast · Reversible
△
G3P
Aldehyde · active
✅ Continues × 2!
⚡ Critical Insight — Everything Doubles From Here!
After this step we have TWO G3P molecules per glucose. All energy yields in Stages 6–10 happen twice. Every ATP and NADH you see from now on is already multiplied ×2!
🎮 Game Analogy
Two-for-one trade! The split gave you one regular coin (G3P) and one foreign coin (DHAP). The machine only accepts regular coins — so you exchange the foreign one. Now you have two identical coins to spend!
🎯 Key Points
✅ DHAP and G3P are structural isomers
✅ Enzyme: Triose Phosphate Isomerase
✅ Near equilibrium — very fast reaction
✅ Result: 2 G3P per glucose — all future steps × 2
📝 Challenge Questions
QUESTION 1 OF 3
What is the final outcome after Stage 5's conversion?
Stage 4 gave 1 G3P + 1 DHAP. Stage 5 converts DHAP INTO G3P. Count how many G3P you have now!
QUESTION 2 OF 3
Why must DHAP be converted to G3P before continuing?
DHAP's tag says "dead end" — what does that tell you about its options?
QUESTION 3 OF 3
How many G3P molecules exist per glucose after Stage 5?
G3P → 1,3-BPG: Oxidation and first energy capture!
△
G3P
Aldehyde · 3C
1 phosphate
⚗️
G3P Dehydrogenase
+1 NADH
⚡△
1,3-Bisphosphoglycerate
1,3-BPG
2 phosphatesHigh energy!
🔋 First Payoff! Per glucose: 2 NADH
NAD⁺ is reduced to NADH + H⁺. The new phosphate comes from free inorganic phosphate (Pi) in the cytosol — NOT from ATP. This creates a high-energy acyl phosphate bond, primed for ATP synthesis!
🎮 Game Analogy
Charging a power bank! You crack open a glow stick (G3P). The chemical reaction releases light energy that gets captured in a rechargeable battery (NADH) for later use, while also loading a spring (1,3-BPG) ready to release ATP!
Direct phosphate transfer from 1,3-BPG to ADP → ATP. No oxygen needed! Happens ×2 per glucose = 2 ATP. This exactly RECOUPS the 2 ATP invested in Stages 1 and 3!
🎮 Game Analogy
Cashing a high-value check! You have a cashier's check (1,3-BPG). The bank (PGK) transfers the energy into cash (ATP). The check becomes regular paper (3-PG) after cashing. Two checks = 2 cash payments!
🎯 Key Points
✅ Substrate-level phosphorylation — direct transfer
✅ No oxygen required — purely anaerobic!
✅ 1 ATP per G3P × 2 G3P = 2 ATP per glucose
✅ Running total: 2 invested − 2 earned = net zero so far
📝 Challenge Questions
QUESTION 1 OF 3
What exactly is "substrate-level phosphorylation"?
"Substrate" = the organic molecule itself. The phosphate travels FROM the substrate DIRECTLY to ADP.
QUESTION 2 OF 3
How many ATP are produced from Stage 7 per glucose molecule?
×2 rule! Two 1,3-BPG molecules (one per G3P), each donates 1 phosphate to ADP. Total?
QUESTION 3 OF 3
Why is Stage 7 called the "Payday"?
You invested 2 ATP early. This step returns exactly 2 ATP. What does that do to your balance?
🎉 Stage 7 Complete! ⚡ 2 ATP — break even!
STAGE 8 OF 10 · HARVEST PHASE
Phosphate Shuffle 🎲
3-PG → 2-PG: Moving the phosphate for the final payoff!
△
3-Phosphoglycerate
Phosphate at C3
End position
🔄
PG Mutase
No energy change
△
2-Phosphoglycerate
Phosphate at C2
Center position
🎮 Game Analogy
Fine-tuning an engine before the final race! You move a spark plug from the back (C3) to the center position (C2) for better ignition. Same engine, better spark placement — ready for maximum power output in Stage 9!
🎯 Key Points
✅ Phosphate moves from C3 → C2
✅ Enzyme: Phosphoglycerate Mutase
✅ Near equilibrium — very fast reaction
✅ No energy change — pure preparation step
📝 Challenge Questions
QUESTION 1 OF 3
What does phosphoglycerate mutase do?
A "mutase" moves a functional group within the same molecule. Look at the molecule tags!
QUESTION 2 OF 3
Why is moving the phosphate from C3 to C2 necessary?
Stage 9 is dehydration. Removing water from C2 creates the high-energy bond. Why does position matter?
QUESTION 3 OF 3
What is the energy change in this mutase reaction?
Moving furniture around doesn't cost or produce energy. Same idea here!
🎉 Stage 8 Complete! Ready for the final stretch!
STAGE 9 OF 10 · HARVEST PHASE
Power Concentration 💧→🔥
2-PG → PEP: Removing water concentrates maximum energy!
△
2-Phosphoglycerate
Phosphate-ester bond
Low energy bond
💧
Enolase
−H₂O removed
🔥△
Phosphoenolpyruvate
PEP
🔥 HIGHEST energy bond!
🔥 PEP = Highest Energy Phosphate Bond in Glycolysis!
Removing H₂O creates an enol phosphate bond — extremely unstable and packed with potential energy. This is the most energetic bond in the entire pathway, perfectly primed for the final ATP jackpot!
🎮 Game Analogy
Concentrating fuel! Start with dilute juice (2-PG) and boil off the water → super-concentrated syrup (PEP). Same substance, but now packed with enormous potential energy. Ready to explode into ATP!
🎯 Key Points
✅ Dehydration: H₂O removed from molecule
✅ Creates enol phosphate — highest energy bond
✅ Enzyme: Enolase (requires Mg²⁺ cofactor)
✅ Irreversible under cellular conditions
📝 Challenge Questions
QUESTION 1 OF 3
What makes PEP unique compared to other molecules in glycolysis?
The 🔥 icon on PEP represents fire — massive energy potential. What makes it special?
QUESTION 2 OF 3
What small molecule is removed by enolase to create PEP?
"De-HYDR-ation" — break it down: de = remove, HYDR = water. What is removed?
QUESTION 3 OF 3
Why is removing water so critical at this step?
Removing water = concentrating energy, like reducing juice to syrup. More concentrated = ?
🎉 Stage 9 Complete! 🔥 PEP is charged and ready!
STAGE 10 OF 10 · GRAND FINALE 🏆
Grand Finale 💥
PEP → Pyruvate: The ultimate ATP jackpot!
🔥△
PEP
Max energy bond
Loaded and ready!
💥
Pyruvate Kinase
+2 ATP total!
🎯
Pyruvate
3-carbon end product
🏆 Final product!
🎰 JACKPOT! Net gain = +2 ATP per glucose!
PEP's phosphate transfers directly to ADP → ATP. Irreversible (ΔG ≈ −31 kJ/mol — massive!). Happens ×2 per glucose = 2 more ATP. Final tally: 4 produced − 2 invested = NET +2 ATP per glucose!
🎮 Game Analogy
Cashing lottery jackpot tickets! You have two super-prize tickets (PEP). The lottery office (pyruvate kinase) cashes them — each gives you $2 (ATP). Two tickets = $4 total! The used tickets become pyruvate.
🎯 Final Tally
✅ 4 ATP produced (2 Stage 7 + 2 Stage 10)
⚡ −2 ATP invested (Stages 1 and 3)
🏆 NET GAIN: +2 ATP per glucose
🔋 2 NADH → up to 6 more ATP in mitochondria!
📝 Final Challenge Questions
QUESTION 1 OF 3
Why is the pyruvate kinase reaction irreversible?
Think of an explosion — massive energy release makes it impossible to reverse. Same principle!
QUESTION 2 OF 3
What is the NET ATP gain per glucose molecule from all of glycolysis?
Stage 7: 2 ATP + Stage 10: 2 ATP = 4 gross. Minus 2 invested (Stages 1 & 3). Net = ?
QUESTION 3 OF 3
What happens to the phosphate group from PEP?
Substrate-level phosphorylation: P moves FROM PEP DIRECTLY to ADP. ADP + P = ?
🏆 GLYCOLYSIS MASTERED! All 10 Stages Complete!
🏆 Glycolysis Grand Master!
All 10 stages conquered — you know glycolysis inside out!
4
ATP Produced
−2
ATP Invested
+2
Net ATP
2
NADH Made
0
Your XP
0%
Accuracy
Stages 1–3 Investment: spent 2 ATP to activate and trap glucose
Stage 10 Pyruvate Kinase: 2 more ATP = NET +2 ATP per glucose!
🚀 What Happens Next?
The 2 NADH enter the electron transport chain in mitochondria, each producing ~2.5 more ATP. Pyruvate enters the Krebs cycle — that's where the massive energy harvest (26–28 more ATP per glucose!) really begins!
