Electron Transport Chain

Electron Transport Chain

Mitochondrial Structure

Electron Transport Chain Overview

The ETC removes energy stored in the NADH and FADH2 molecules to:

1. create a proton gradient across the inner mitochondrial membrane

2. convert O2 to H2O.

All reactions are redox reactions.

Electron Transport Chain Animation

ETC Animation

ETC Components

ETC Components: Complex I2 e- from NADH are

transferred to Complex I

Protons are pumped across the inner mitochondrial membrane (IMM) by Complex I

ETC Components: Qe- are transferred from

Complex I to ubiquinone (Q)

Q is a mobile component within the IMM

ETC Components: Complex III

e- are transferred from Q to Complex III

Protons are pumped across the IMM by Complex III

ETC Components: Cyt Ce- are transferred from

Complex III to cytochrome c (cyt c)

cyt c is a mobile component on the surface of IMM, in the intermembrane space

ETC Components: Complex IV

e- are transferred from cyt c to Complex IV

Protons are pumped across the IMM by Complex IV

ETC Components: O2

O2 is the final electron acceptor of the ETC

enough e- pass through the ETC to produce full H2O molecules

FADH2 Pathway

FADH2 FAD

ETC Components: Complex II2e- are transferred from

FADH2 to Complex II – can think of them passing directly to Ubiquinone

no protons are pumped across the IMM

e- are transferred from Complex II to Q and proceed through the rest of ETC

FADH2 FAD

ETC Thermodynamics

Each electron transfer step is energetically favourable.

Electrochemical Proton Gradient

ETC Summary

1. NADH e- transferred to O2; three proton pumps activated

2. FADH2 e- transferred to O2; two proton pumps activated

3. electrochemical proton gradient formed across IMM

Electron Transport Chain Animation

ETC Animation

Oxidative Phosphorylation

Proton Motive Force: ChemiosmosisThe electrochemical gradient (chemiosmosis)

produced by the ETC can now be used to generate ATP through the process of oxidative phosphorylation (OXPHOS).

OXPHOS occurs through the enzyme complex ATP synthase.

OXPHOS Animation

ATP Synthase ComplexTwo components:

1. F0 – proton channel / rotor embedded in IMM

2. F1 – catalytic sites that phosphorylate ADP to ATP

ATP synthase rotation

ATP Productionoxidative phosphorylation - ATP is produced as

protons flow through ATP synthase.

In general:

1. 1 NADH 2.5 – 3 ATP molecules

2. 1 FADH2 1.5 – 2 ATP molecules

The ETC is coupled with ATP synthesis. The latter is dependent on the former.

ATP ProductionCellular

Respiration Step

Energy Molecules Produced

ATP Totals

Glycolysis 2 ATP2 NADH

2 ATPspecial case

Oxidative Decarboxylation

2 NADH 6 ATP

Krebs Cycle 6 NADH2 FADH2

2 ATP

18 ATP4 ATP2 ATP

Glycolysis NADHNADH produced in glycolysis must be transported

from the cytoplasm into the mitochondria to enter the ETC.

Two shuttle mechanisms:

1. glycerol phosphate shuttle

2. malate-aspartate shuttle

Glycerol Phosphate Shuttle

Malate-Aspartate Shuttle

ATP Production SummaryCellular

Respiration Step

Energy Molecules Produced

ATP Totals

Glycolysis 2 ATP2 NADH

2 ATP4-6 ATP

Oxidative Decarboxylation

2 NADH 6 ATP

Krebs Cycle 6 NADH2 FADH2

2 ATP

18 ATP4 ATP2 ATP

TOTAL 36-38 ATP