Pentose Phosphate Pathway Tournament
Two onboarding diagrams place the PPP in carbohydrate metabolism. Then eight MCAT-DoK quiz rounds: why NADPH (and not NADH) keeps glutathione reduced, the cascade behind fava-bean hemolysis, the three-step oxidative phase, what transketolase has to do with thiamine deficiency, and which classic PPP outputs you should recognize.
Where the Pentose phosphate pathway fits in Metabolism of carbohydrates
The PPP branches off glucose-6-phosphate from glycolysis to make NADPH (the cell's reducing power for biosynthesis and antioxidant defense) and ribose-5-phosphate (the sugar backbone of every nucleotide). To enter the tournament, click the highlighted Pentose phosphate pathway box.
Click the highlighted Pentose phosphate pathway box to continue.
What this tournament tests
Each task maps to a distinct MCAT cognitive demand. The first two orient you in the broader topology; the next eight test the high-yield mechanism, regulation, sequence and quantitative reasoning that consistently appear on test day.
The Bigger Picture
Locate the PPP inside Reactome's Metabolism of Carbohydrates overview.
Whole-Pathway Overview
Pan and zoom the curated WikiPathways PPP figure before you play.
Fill in the Blank
Recall NADPH as the cell's universal reducing power for biosynthesis and antioxidant defense.
Disruptor
Walk the G6PD-deficiency / fava bean / Heinz-body / hemolysis chain.
Sequence Ordering
Order G6P -> 6PGL -> 6PG -> Ru5P -> R5P through the oxidative phase.
Match the Pairs
Pair each PPP enzyme with its specific job - oxidative vs non-oxidative phase.
Numeric Input
Count the NADPH yield per G6P consumed by the oxidative phase.
Select All That Apply
Identify the true PPP statements from common MCAT confusions.
Odd One Out
Spot the molecule that is NOT a PPP product.
Thiamine Cofactor
Recall transketolase as the TPP-dependent enzyme - the basis of the RBC thiamine assay.
Public leaderboard
Your score posts to a global, persistent leaderboard scored by points first, time as tiebreaker.
Pentose phosphate pathway in 60 seconds
The PPP is a cytosolic detour off glucose-6-phosphate. The oxidative phase (G6PD, lactonase, 6PGD) makes 2 NADPH + 1 CO2 + 1 ribulose-5-P per G6P. The non-oxidative phase (transketolase, transaldolase) reshuffles 5-carbon sugars to/from glycolysis - reversible, runs whichever way the cell needs.
G6PD is rate-limiting and feedback-regulated by NADPH/NADP+. Its deficiency is the most common human enzymopathy and shows up as oxidant-triggered hemolysis (favism, primaquine, sulfas) - because RBCs depend entirely on PPP-derived NADPH to keep glutathione reduced.
Different cell states use the PPP differently. Lipogenic liver / adipose: oxidative phase HIGH (NADPH-hungry FAS), non-oxidative phase REVERSED to recycle excess R5P back to F6P/G3P. Proliferating cells: more R5P than NADPH, non-oxidative phase runs FORWARD. RBCs: NADPH-only, both phases bent toward antioxidant defense.
Transketolase is TPP (thiamine)-dependent - its activity in RBCs is the gold-standard biomarker for B1 deficiency (Wernicke encephalopathy). Transaldolase, by contrast, has no cofactor.
FAQ
Why is NADPH (and not NADH) the antioxidant currency?
NADPH/NADP+ ratio is kept high (~100:1, REDUCED) so it can drive thermodynamically uphill reductions like GSSG -> 2 GSH. NADH/NAD+ is kept low (~1:1000, OXIDIZED) to drive catabolic dehydrogenation. The cell deliberately runs these two pools in opposite redox states.
Why are RBCs so vulnerable to G6PD deficiency?
RBCs have NO mitochondria, NO nuclei, and NO new protein synthesis. They cannot upregulate residual G6PD or replace damaged enzyme. The PPP is their only NADPH source. Any oxidant load that exceeds residual GSH causes Heinz-body formation and hemolysis.
Do I need an account to play?
No. The tournament is fully public. You get a randomized handle and your score posts to the public leaderboard at the bottom of this page.
Keep going
Where the G6P that feeds the PPP comes from - and the regulatory switch that decides 'glycolysis vs PPP'.
The biggest customer of PPP-derived NADPH: each palmitate costs 14 NADPH.
Overview diagram: Reactome Pathway R-HSA-71387, licensed CC BY 4.0.