electron transport chain

In the electron transport chain, are electrons donated to components with more negative or more positive redox potentials?

Electrons are donated from components with more negative redox potentials to components with more positive redox potentials.

Where is the electron transport chain located

• Eukaryotes: Inner mitochondrial membrane

• Prokaryotes (bacteria): Plasma membrane

As electrons move down the electron transport chain, what happens to protons? Is there a higher proton concentration in the matrix or the intermembrane space?

• Protons (H⁺) are pumped from the matrix into the intermembrane space.

• This creates a higher proton concentration in the intermembrane space compared to the matrix.

What is the purpose of the proton gradient? Does the cell need an intact membrane for ATP synthesis?

• The proton gradient powers ATP synthesis via the enzyme ATP synthase.

• Yes, the cell absolutely needs an intact, closed membrane to maintain the gradient. Without it, protons leak and ATP cannot be made efficiently.

• This is the chemiosmotic hypothesis: energy from electron transport is stored in the form of a proton gradient, which drives ATP production.

Why is the complete oxidation of glucose more efficient than glycolysis in terms of energy production?

• Glycolysis alone yields 2 ATP per glucose.

• Complete oxidation (glycolysis + TCA + ETC) yields ~36 ATP per glucose.

• This efficiency comes from:

  • NADH and FADH₂ feeding high-energy electrons into the ETC.

  • Electrons driving proton pumping, which powers ATP synthesis (oxidative phosphorylation).

Where is oxygen used in the electron transport chain?

• Oxygen acts as the final (terminal) electron acceptor at Complex IV (cytochrome a + a₃).

• It combines with electrons and protons to form water (H₂O).

• Without oxygen, electrons back up in the chain, halting ATP production.

What types of molecules cause phosphofructokinase (PFK) to speed up or slow

• Answer:

  • Inhibitors (slow down PFK):

    • ATP (when energy is abundant)

    • Citrate

  • Activators (speed up PFK):

    • ADP and AMP (signals of low energy)

• PFK is a rate-limiting enzyme in glycolysis. It is allosterically regulated to balance energy production with cellular needs.

Can a cell take up lactose in the absence of oxygen?

• Answer: Yes, but only if it can maintain a proton gradient through fermentation.

• In E. coli, lactose uptake depends on a symport mechanism that uses the proton gradient.

• If oxygen is absent, the ETC stops, but fermentation can regenerate NAD⁺ to allow glycolysis to continue, maintaining enough proton motive force for lactose uptake—unless uncouplers like DNP disrupt the gradient.