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Unit 4 • Energetics & Respiration

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Do first
Redox bookkeeping: track carbons and electron carriers per glucose across stages.
ETC inhibition intuition: cyanide/rotenone stop at specific complexes → upstream NADH buildup, no gradient.
Respiratory control: high ATP or citrate feedback inhibits phosphofructokinase (PFK).
Chemiosmosis universality: compare mitochondria, chloroplasts, bacteria (pmf across membranes).

Thermo & ∆G

1st Law: energy conserved. 2nd Law: every transfer increases entropy (heat loss). ∆G < 0 → spontaneous/exergonic; ∆G > 0 → endergonic.

Energy coupling: ATP hydrolysis drives endergonic steps via phosphorylation; phosphorylated intermediates become more reactive.

Enzymes & Inhibition

Enzymes lower Ea; do not change ∆G or equilibrium.

Regulation: allosteric effectors, covalent mods (phosphorylation), feedback inhibition.

Temperature/pH and substrate concentration shift rate; carriers saturate similar to enzymes.

Competitive

  • • Binds active site; resembles substrate
  • • High substrate can outcompete
  • • Vmax unchanged; Km increases (need more substrate)

Noncompetitive/allosteric

  • • Binds other site → shape change
  • • Adding substrate cannot restore full rate
  • • Lowers effective enzyme concentration; Vmax drops

Respiration Flow

Track electrons
Glycolysis (cytosol): glucose → 2 pyruvate + 2 NADH + net 2 ATP.
Link reaction (matrix): pyruvate → acetyl-CoA + NADH + CO₂.
Citric acid cycle (matrix): per acetyl-CoA → 3 NADH + FADH₂ + GTP/ATP + 2 CO₂.
ETC + oxidative phosphorylation (inner membrane): electron flow pumps H⁺ to intermembrane space; ATP synthase uses gradient to make ATP (~26-28). O₂ is final e⁻ acceptor → H₂O.
Anaerobic: fermentation regenerates NAD⁺ (lactate or ethanol + CO₂); yields 2 ATP per glucose.

NAD⁺ → NADH

Reduced with H⁻; carries high-energy electrons to ETC (3 ATP per pair theoretical).

FAD → FADH₂

Enters ETC at complex II; yields ~2 ATP per pair theoretical.

Inhibitor logic: block complex IV (cyanide) → no O₂ reduction → no gradient → ATP synthase stops. Uncouplers leak H⁺ → heat instead of ATP.