Electron Transport Chain (ETC) Flashcards
Describe the Structure + Function of Mitochondria (Only relevant to ETC)
Matrix:
-Site of Oxidative Metabolism pathways
Cristae:
- Increase SA
-Allows more ETC complexes to be packed in the membrane, boosts ATP production.
Intermembrane Space:
- Semi-permeable compartment, retains proteins + large ions
Inner membrane:
- Impermeable to ions
-Contains transporters for metabolites e.g. Pyruvate, Citrate
Can Energy be stored in Ion Gradients?
Yes
What is the Concept of Oxidative Phosphorylation?
Chemiosmotic Theory: Using ionic gradients to produce energy
- Electrons from NADH + FADH2 flow through complexes in inner mitochondrial membrane
- Electrons drive proton export to intermembrane space
- Proton gradient established
- Proton Gradient used by ATP Synthase
- ADP Phosphorylated = ATP Produced
How does the ETC allow energy to be obtained?
It allows energy to be obtained in small amounts from NADH/FADH2 in a series of redox reactions.
What Enzymes are involved in the ETC? (Give the Correct Order)
Complex I: NADH-CoQ Reductase
Complex II: Succinate-CoQ Reductase
Complex III: CoQ-Cytochrome C Oxireductase
Complex IV: Cytochrome C Oxidase
How many Protons does each Complex Pump?
NADH-CoQ Reductase: 4 for every 2e-
Succinate-CoQ Reductase: none
CoQ-Cytochrome C Oxireductase: 4 for every 2e-
Cytochrome C Oxidase: 2 for every 2e-
Order of Complexes In Terms Of Size (kDA), Biggest to Small.
Complex I: 880 kDa
Complex II: 140 kDa
Complex III: 250 kDa
Complex IV: 160 kDa
What is the Role Of Complex I?
Accepts 2 electrons from NADH produced in TCA Cycle/Glycolysis
Transfers Electrons to CoQ, converts it to CoQH2
CoQ: Ubiquinone
CoQH2: Ubiquinol
What Is the role Of Complex II (Succinate Co-Q Reductase) ?
- Accepts 2 electrons from FADH2
- Transfers electrons to CoQ
- Complex I bypassed
- Electrons fed into Complex III
What Is The Role of Complex III?
Accepts electrons from CoQH2, transfers them to Cytochrome C
Pumps 4 protons per 2 electrons
What is the Role Of Complex IV?
Accepts 2 electrons from Cytochrome C, transfers them to Oxygen, forming Water
2 Protons pumped per 2 electrons
Name the ETC Mobile Co-Factors and their function.
Co-enzyme Q:
- Hydrophobic, lipid soluble
- Carries Protons (H)
- Transfers electrons from C1-C2 to C3
Cytochrome C:
- Polar, Water Soluble small Protein
- Carries Electrons from C3 to C4
- it does not carry Protons (H)
What are the ETC Embedded Co-Factors?
FAD/FMN:
- Water-soluble, protein bound (sometimes)
- Carries Electrons and Hydrogens
Iron-Sulfur Clusters (Fe-S):
- Always protein-bound
- Carries electrons.
Which Electron carriers /Co-Factors are Lipophilic?
CoQ (Ubiquinone) is the lipophilic electron carrier/cofactor in the electron transport chain (ETC).
Explanation:
CoQ (Ubiquinone):
Small, lipid-soluble molecule that freely diffuses within the inner mitochondrial membrane’s lipid bilayer.
Shuttles electrons between Complex I/II → Complex III.
Lipophilicity allows it to act as a mobile electron carrier in hydrophobic membrane environment.
Which electron carriers / cofactors carry hydrogens and which carry only electrons?
FAD,FMN and CoQ Carry Enzymes
What is the correct pathway for passage of electrons through the electron transport chain?
Complex I > Complex II > Complex III > Complex IV
Complex II > Complex I > Complex III > Complex IV
Complex I or Complex II > Complex III > Complex IV
Complex I or Complex II > Complex III > Complex IV
Which end of the chain is most reducing (-ve redox potential)?
Complex I
Complex II
Complex IV
Complex I
Describe the journey of an electron starting from NADH (produced in TCA Cycle) all the way to its final destination (O2).
List the specific ETC complexes + carriers it passes through.
NADH → Complex I (NADH Dehydrogenase) →
CoQ (Ubiquinone) → Complex III (Cytochrome bc₁) → Cytochrome c → Complex IV (cytochrome c oxidase) → Oxygen (final acceptor).
Protons pumped: 4 (Complex I) + 4 (Complex III) + 2 (Complex IV) = 10 protons total.
How does the journey of an electron from FADH₂ differ from NADH’s?
FADH₂ → Complex II (succinate dehydrogenase) → CoQ → Complex III → Cytochrome c → Complex IV → Oxygen.
Protons pumped: 0 (Complex II) + 4 (Complex III) + 2 (Complex IV) = 6 protons total.
Why does FADH₂ Yield less ATP?
- Complex I Pumps 4 protons
- FADH₂ skips Complex I
- Fewer Protons added to the gradient
- Less ATP Synthesized
