Redox Potentials and the Proton-Motive Force · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Falling electrons, pumped protons

Science · Biochemistry & Molecular Biology · ages 20-21
Name ______________________   Date ____________

  1. What are the two components of the proton-motive force?

    • Heat and light released by the chain
    • A pH difference and a membrane voltage, with voltage dominant
    • Gravity and friction inside the mitochondrion

  2. In which order do electrons travel along the chain?

    • From NADH down ordered carriers to oxygen as the final acceptor
    • From oxygen upward to NADH against the potential
    • In a circle that never reaches any acceptor

  3. Why does respiration stop without oxygen?

    • Electrons pile up with no final acceptor to take them
    • The membrane dissolves instantly without oxygen
    • NADH refuses to donate electrons ever again

  4. An uncoupler lets protons leak back past ATP synthase. What happens?

    • Electron flow speeds up while ATP production collapses
    • Both electron flow and ATP production stop together
    • ATP production rises while electron flow slows

  5. Two electrons fall across 0.1 volts. Using 96.5 kJ per volt per mole, how much energy per mole is released? Give kJ per mole.

    Answer: ______________

  6. NADH gives its electrons to the next carrier. What is NADH now?

    • Oxygen gas ready to leave the cell
    • NAD plus, the oxidized form after donating
    • A proton stuck inside the membrane

  7. Electrons flow from high to low reduction potential, releasing energy as they climb.

    Circle one:   True   False

  8. A new chemical lets protons leak freely. Flow doubles but ATP halves. What does this prove?

    • The chain makes ATP directly with no intermediate
    • Oxygen is unnecessary for ATP production
    • The gradient is the true intermediate between flow and ATP
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Falling electrons, pumped protons W1-mt_lU8kgepFRN-s1

  1. A pH difference and a membrane voltage, with voltage dominant · Concentration plus voltage push protons home. In mitochondria the voltage push dominates.
  2. From NADH down ordered carriers to oxygen as the final acceptor · Downhill order toward oxygen is the whole design. Reversing it would absorb energy instead of releasing it.
  3. Electrons pile up with no final acceptor to take them · No acceptor means no flow. A chain with a blocked end backs up completely.
  4. Electron flow speeds up while ATP production collapses · The leak removes resistance to flow but bypasses the ATP maker. Flow without harvest is the signature split.
  5. 19.3 · Multiply electrons by the constant by the volts. That product prices the step.
  6. NAD plus, the oxidized form after donating · Donating electrons is oxidation. The donor keeps its oxidized name: NAD plus.
  7. False · They fall from low to high potential toward oxygen. Climbing would absorb energy, not release it.
  8. The gradient is the true intermediate between flow and ATP · Only a gradient in the middle explains the split. Bypassing it keeps flow while killing harvest.
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