Oxidative phosphorylation (ETC)

Question 1

What is the structure of the mitochondria?

Answer 1

🧬 Mitochondria Overview

Structure: Double membrane (evidence of endosymbiosis—origin from a prokaryote).
Outer membrane: Contains porins, is permeable to small molecules.
Inner membrane: Impermeable to polar molecules; crucial for ATP production.
Highly folded into cristae to increase surface area (~14,000 m² in a human body).
Contains ~40 specific transporters/shuttles.

Question 2

What are the 2 NADH shuttles?

Answer 2

NADH from glycolysis cannot cross the mitochondrial membrane directly, so:

Glycerol-3-phosphate shuttle (muscle):
Transfers electrons to FAD → less ATP (~1.5 ATP/NADH).
Malate–aspartate shuttle:
Transfers electrons to NAD+ inside mitochondria → more ATP (~2.5 ATP/NADH).

Question 3

What is ATP-ADP translocase?

Answer 3

Exchanges ATP (more negative) for ADP across inner membrane.
Uses the electrical gradient, consuming ~25% of the proton motive force

Question 4

What are the redox basics?

Answer 4

OILRIG: Oxidation Is Loss, Reduction Is Gain (of electrons).
Standard Reduction Potential (E°):
High E° = more likely to gain electrons (strong oxidiser).
ΔE° = E°(acceptor) - E°(donor).
Related to Gibbs Free Energy:
ΔG = -nFΔE° (F = Faraday’s constant = 96.5 kJ/V·mol).

Question 5

What is Complex I – NADH-CoQ Oxidoreductase?

Answer 5

NADH → Coenzyme Q (CoQ).
Cofactors: FMN (1e⁻ at a time), 6-7 Fe-S clusters.
Pumps protons across inner membrane.

Question 6

What is Complex II – Succinate-CoQ Oxidoreductase?

Answer 6

Linked directly to TCA cycle (via succinate dehydrogenase).
Uses FAD, Fe-S, and cytochrome b560.
Does NOT pump protons.

Question 7

What is Coenzyme Q (Ubiquinone)?

Answer 7

Lipid-soluble electron carrier.
Shuttles electrons from Complex I/II → Complex III.

Question 8

What is Complex III – CoQ-Cytochrome c Oxidoreductase?

Answer 8

Transfers e⁻ to cytochrome c via Fe-S and cytochromes b and c1.
Pumps protons.

Question 9

What is Cytochrome c?

Answer 9

Small, mobile, water-soluble.
Carries e⁻ from Complex III → IV.

Question 10

What is Complex IV – Cytochrome c Oxidase?

Answer 10

Accepts e⁻ from Cyt c → O₂ (forms water).
Cofactors: cytochrome a, a3, CuA and CuB.
Pumps protons.

Question 11

What is the efficiency and ATP yield of the ETC?

Answer 11

💥 Efficiency & ATP Yield

NADH oxidation releases ~220 kJ/mol.
1 ATP = 30.5 kJ/mol.
Yield:
~2.5 ATP per NADH (via malate-aspartate shuttle).
~40% efficiency (remainder lost as heat).

Question 12

What are ☠️ Reactive Oxygen Species (ROS) and what defence is there?

Answer 12

Side-products of incomplete O₂ reduction (e.g., superoxide, H₂O₂).
Damage membranes, proteins, DNA.
Defense:
Superoxide dismutase (SOD): converts superoxide → H₂O₂.
Catalase: converts H₂O₂ → H₂O + O₂.

Question 13

What are ETC inhibitors?

Answer 13

🚫 ETC Inhibitors

Complex I: Rotenone, Amytal.
Complex IV:
Cyanide, azide: inhibit Fe³⁺ in cytochrome a3.
CO: binds to Fe²⁺ in cytochrome a3.

Question 14

What is the overall role of ox-phos?

Answer 14

Proton gradient generated by ETC.
Drives ATP synthesis via ATP synthase.
Chemiosmotic theory: Proton motive force (PMF) powers ATP production.
Gamma subunit rotates inside ATP synthase (50–100x/sec), changing conformation of β-subunits → ATP formation.

Question 15

How is ox-phos controlled?

Answer 15

Driven by ADP availability (i.e., ATP demand).
ETC & ATP synthase are tightly coupled:
No ADP or O₂ = no electron flow = no ATP made.
Most mitochondria are tightly coupled, meaning:
No uncoupling unless intentionally induced (e.g., by uncoupling proteins in brown fat).