Electron Transport Chain Tournament
Two onboarding diagrams orient you in aerobic respiration. Then eight MCAT-DoK quiz rounds: where FADH2 enters, why DNP kills, which complex each classic inhibitor targets, the canonical 10 H+ per NADH, and how cytochrome c moonlights as an apoptosis signal.
Where the Respiratory electron transport fits in Aerobic respiration & respiratory electron transport
The electron transport chain is the inner-membrane endpoint of aerobic respiration. NADH and FADH2 produced by glycolysis, pyruvate oxidation, and the TCA cycle all converge here, dropping electrons through Complexes I/III/IV (and II for FADH2) so the freed energy can be stored as a proton gradient. To enter the tournament, click the highlighted Respiratory electron transport box.
Click the highlighted Respiratory electron transport 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
Anchor the ETC in aerobic respiration on the live Reactome overview map.
Whole-Pathway Overview
Pan and zoom the curated WikiPathways ETC figure before you start answering.
Fill in the Blank
Recall that FADH2 enters at Complex II, bypassing Complex I and one pumping site.
Disruptor
Predict why DNP uncoupling collapses ATP while spiking heat and O2 demand.
Sequence Ordering
Order NADH -> Complex I -> Q -> Complex III -> cyt c -> Complex IV -> O2.
Match the Pairs
Pair each classic ETC inhibitor with the complex (or membrane site) it disables.
Numeric Input
Sum the H+ pumped by Complexes I + III + IV per pair of NADH electrons.
Select All That Apply
Discriminate true ETC facts from common MCAT confusions (Q is a lipid, not a protein).
Odd One Out
Tell electron carriers apart from the F1 catalytic rotor of ATP synthase.
Cell Death Crossover
Recognize cytochrome c's second job: triggering apoptosis once it leaves the IMS.
Public leaderboard
Your score posts to a global, persistent leaderboard scored by points first, time as tiebreaker.
ETC in 60 seconds
The electron transport chain runs along the inner mitochondrial membrane and converts the reducing power of NADH and FADH2 into a proton gradient. Electrons travel NADH -> I -> Q -> III -> cyt c -> IV -> O2 while H+ is pumped at Complexes I, III, IV.
Complex II never pumps protons - it just feeds FADH2 electrons into Q. That single fact is why FADH2 gives ~1.5 ATP and NADH ~2.5 ATP. Per NADH the chain pumps ~10 H+ total: 4 (I) + 4 (III) + 2 (IV).
The MCAT loves the inhibitor toolbox: rotenone at I, antimycin A at III, cyanide / CO at IV, oligomycin at ATP synthase, and DNP as a membrane-permeabilizing uncoupler.
Cytochrome c moonlights: it shuttles electrons between Complex III and IV during respiration AND triggers the intrinsic apoptosis pathway when Bax/Bak permeabilize the outer membrane. One molecule does the work of life and death.
FAQ
How many ATP does one NADH ultimately yield via the ETC?
Roughly 2.5 ATP per NADH and 1.5 ATP per FADH2 under canonical chemiosmotic stoichiometry. NADH enters at Complex I (4 H+), FADH2 at Complex II (0 H+), so FADH2 misses one full pumping site.
Why does cyanide kill so quickly?
Cyanide binds Fe3+ in heme a3 of Complex IV with high affinity, blocking the terminal electron transfer to O2. The entire ETC stalls within seconds, ATP collapses, and O2 cannot be reduced no matter how much is inhaled.
Why is Complex II not numbered like the others if it doesn't pump protons?
Numbering follows the order of mitochondrial isolation, not function. Complex II = succinate dehydrogenase, the only TCA enzyme physically embedded in the inner membrane. It transfers electrons to Q but contributes nothing to the proton gradient.
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
ATP synthase mechanics, P/O ratios, chemiosmotic coupling and the proton motive force.
TCA enzymology, NADH/FADH2/GTP/CO2 yield per turn - feeding the ETC you just played.
Overview diagram: Reactome Pathway R-HSA-1428517, licensed CC BY 4.0.