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OperonBiology
AP BiologyOlympiad

Cellular Respiration

Glycolysis → pyruvate oxidation → Krebs cycle → oxidative phosphorylation, with inhibitors, uncouplers, O₂ supply and ATP demand.

Glycolysis & fermentationPyruvate oxidation & the Krebs cycleOxidative phosphorylation & chemiosmosisEnergy coupling & ATP

1. Glycolysis & fermentation

Cytosol

Glucose is split into two pyruvate in the cytosol, netting 2 ATP and 2 NADH. When mitochondria can't take the electrons, lactate dehydrogenase regenerates NAD⁺ instead.

  • Investment phase: 2 ATP spent (hexokinase, PFK-1)
  • Payoff phase: 4 ATP by substrate-level phosphorylation, 2 NADH
  • PFK-1 is inhibited by ATP and citrate, activated by AMP
  • Fermentation recycles NAD⁺ but makes no extra ATP

cellular-respiration · stage 1/5

CytosolMitochondrial matrixInner membraneIntermembrane space2 pyruvateLDH2 ATPPFK-1GlucoseGlycolysisPyruvateLactatePDH complexAcetyl-CoAKrebs cycleNADHComplex IComplex IIComplex IIIComplex IVO₂H⁺ gradientATP synthaseADP + PᵢATP
  • Carbon / material flow
  • Electron transfer
  • Activation
  • Inhibition
  • Feedback
  • ▲ 12 change vs. baseline (percentage points)
ATP per glucose
30.3ATP
baseline 30.3 ATP
ATP demand met
100%
baseline 100%
O₂ consumption
100% of rest
baseline 100% of rest
Glucose use
100% of rest
baseline 100% of rest
Pyruvate → lactate
0%
baseline 0%
Proton-motive force
170mV
baseline 170 mV
NAD pool reduced
40%
baseline 40%
Respiration uncoupled
6%
baseline 6%

Impact

No changes from baseline.

Change a variable or apply a scenario. This panel then shows what moved, which direction the effect travelled, and why.

Inspect a step

Select any node on the diagram to see what it does, its inputs and outputs, and how it compares with baseline.