Lecture 3B.1: Respiration: Electron Transport Chain (ETC) & ATP Production Flashcards
Energy Production and Primary Metabolism
Respiration: Electron transport chain
REDOX REACTIONS: low-potential electron donors (more __) are and the resulting electrons are driven through ___ by their affinity for a high-potential __
- electronegative
- electron transport chain
- electron acceptor
This measures the tendency of a molecule to gain or lose electrons in a redox reaction.
Redox Potential (E₀’)
Additional Info:
* A more negative E₀’ means the substance is a good electron donor (it wants to give up electrons).
* A more positive E₀’ means the substance is a good electron acceptor (it wants to gain electrons).
- This tells us whether a reaction releases energy (exergonic, spontaneous, ΔG < 0) or requires energy input (endergonic, non-spontaneous, ΔG > 0).
- It is related to redox reactions because when electrons flow from a donor to an acceptor with a higher redox potential, energy is released.
Gibbs Free Energy (ΔG)
Relationship of Gibb’s Free energy and Redox Potential in an equation
ΔG′=−nFΔE₀’
ΔG’ = Gibbs free energy change (J/mol)
n = Number of electrons transferre
F = Faraday’s constant (96,485 J/V·mol)
ΔE₀’ = Difference in redox potential between donor and acceptor (V)
What determines electron flow in redox reactions?
Electrons move from a donor with a lower redox potential (E₀’) to an acceptor with a higher redox potential.
What type of molecules serve as low-potential electron donors?
E₀’
Molecules with a more negative E₀’, meaning they readily donate electrons.
What type of molecules serve as high-potential electron acceptors?
E₀’
Molecules with a more positive E₀’, meaning they readily accept electrons.
Give examples of common electron acceptors.
In aerobic and anaerobic conditions
- O₂ (aerobic respiration)
- NO₃⁻, SO₄²⁻, Fe³⁺, CO₂ (anaerobic respiration)
Example for Redox Potential:
NADH (E₀’ ≈ -0.32 V) is a good electron __.
O₂ (E₀’ ≈ +0.82 V) is a good electron __.
Electrons naturally flow from __ → __
- donor
- acceptor
- NADH → O₂
Aerobic/Anaerobic respiration
- Aerobic respirations = __ as the terminal electron acceptor
- Anaerobic respirations = electron acceptors other than __
Oxygen
Why does anaerobic respiration yield less energy than aerobic respiration?
In terms of electron acceptors
Because alternative electron acceptors have a lower redox potential than the O₂/H₂O redox couple, resulting in less energy release.
O₂/H₂O, Em, 7 = +815 mV
Key Differences: Anaerobic Respiration vs. Fermentation
Differentiate in terms of:
* Electron Transport Chain (ETC)
* External Electron Accepto
* Proton Motive Force (PMF)
* ATP Production
* Energy Yield
Anaerobic Respiration:
* YES - Electron Transport Chain (ETC)
* YES (NO₃⁻, SO₄²⁻, etc.) - External Electron Acceptor
* YES - Proton Motive Force (PMF)
* Oxidative phosphorylation (diff e- acceptor) - ATP Production
* Higher (but less than aerobic respiration) - Energy Yield
Fermentation:
* NO - Electron Transport Chain (ETC)
* NO - External Electron Acceptor
* NO - Proton Motive Force (PMF)
* Substrate-level phosphorylation - ATP Production
* Lower - Energy Yield
What determines the amount of ATP produced in an ETC?
The difference in __ between the electron donor and the final electron acceptor. A __ difference generates __ ATP.
- redox potential (ΔE₀’)
- larger
- more
Redox Midpoint Potentials (E₀’, mV) of Key Electron Donors & Acceptors
Determine each role of the redox pair given in Electron Transport Chain (ETC):
1. H₂ / H⁺ (-420 mV)
2. Formate (HCO₂⁻) / CO₂ (-420 mV)
3. NADH / NAD⁺ (-320 mV)
4. FADH₂ / FAD (+31 mV)
5. Succinate / Fumarate (+31 mV)
6. O₂ / H₂O (+815 mV)
7. NO / N₂O (+1,300 mV)
- Strong electron donor
- Electron donor
- Major electron donor
- Intermediate electron carrier
- Intermediate in the ETC
- Final electron acceptor (Aerobic Respiration)
- Alternative acceptor (Anaerobic Respiration)
How much energy can be harvested in bacterial ETC?
Some bacterial ETCs span more than __ (e.g., from NADH to O₂), creating a large __ for __.
- 1V
- proton motive force (PMF)
- ATP synthesis
refers to the difference in redox potential between the initial electron donor (e.g., NADH) and the final electron acceptor (O₂).
Redox span
Aerobic Bacterial Electron Transport Chain:
What is the redox span in aerobic bacterial ETCs?
eV, kcal mol⁻¹, kJ mol⁻¹
More than 1 eV, which corresponds to about 23 kcal mol⁻¹ (96 kJ mol⁻¹).
Aerobic Bacterial Electron Transport Chain:
What is the thermodynamic cost of transporting one proton?
Around 4.6 kcal mol⁻¹ (19.2 kJ mol⁻¹) when PMF is high (~200 mV).
Aerobic Bacterial Electron Transport Chain:
How many protons are pumped per electron in a ~1V redox span?
Up to five protons per electron transferred from donor (e.g., NADH) to acceptor (O₂).
Why does the ETC have a stepwise drop in potential?
- Instead of a single, large energy drop, electron transfer occurs in a stepwise manner through multiple redox centers (e.g., cytochromes, iron-sulfur clusters, quinones) in the ETC.
- This prevents energy from being lost as heat and allows respiratory enzymes to operate at high thermodynamic efficiency
Additional info:
- The stepwise electron flow helps generate and sustain the PMF, ultimately driving ATP production via oxidative phosphorylation.
How does the bacterial cell membrane contribute to respiration?
It serves as an integral part of the __, isolating and storing the __.
- proton-motive machinery
- proton motive force (PMF).
Aerobic Bacterial Electron Transport Chains:
__ help establish __ along the membrane surface and aid in proton uptake in respiratory complexes.
- Lipid headgroups
- proton conduction pathways
Aerobic Bacterial Electron Transport Chains:
Are the exact mechanisms of lipid-mediated proton conduction known?
No, the precise principles are still not fully understood.
Aerobic Bacterial Electron Transport Chains:
It is an assembly of multiple respiratory enzyme complexes that may improve efficiency and regulate activity.
respiratory supercomplex