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 IComplex 1: NADH

Dehydrogenase

2 e- from NADH are transferred to Complex I

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

ETC Components: Qe- are transferred from

Complex I to ubiquinone (Q)

Q is a mobile component within the IMM

ETC Components: Complex IIIComplex III:

Cytochrome b-c1

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 IVComplex IV:

Cytochrome Oxidase

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

Oxidativephosphorylation.

electron transportand chemiosmosis

Glycolysis

ATP ATP ATP

H+

H+H+

Protein complexof electron carners

Cyt c

I

II

III

IV

(Carrying electronsfrom, food)

NADH+

FADH2

NAD+

FAD+ 2 H+ + 1/2 O2

H2O

Electron transport chainElectron transport and pumping of protons (H+),

which create an H+ gradient across the membrane

Q

Intermembranespace

Innermitochondrialmembrane

Mitochondrialmatrix

Figure 9.15

FADH2 Pathway2e- are transferred from

FADH2 to Complex II

no protons are pumped across the IMM

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

ETC Thermodynamics

H2O

O2

NADH

FADH2

FMN

Fe•S Fe•S

Fe•S

O

FAD

Cyt b

Cyt c1

Cyt c

Cyt a

Cyt a3

2 H + + 12

I

II

III

IV

Multiproteincomplexes

0

10

20

30

40

50

Free

ene

rgy

(G) r

elati

ve to

O2 (k

cl/m

ol)

FADH2 enters the chain at a lower energy than NADH

2 electrons from NADH produce a max of 3 ATP

2 electrons from FADH2 produce a max of 2 ATP

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

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.proton channel / rotor

embedded in IMM

2.catalytic sites that phosphorylate ADP to ATP

This is an example of facilitated diffusion (passive transport)

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

Oxidative Decarboxylation

Krebs Cycle

ATP Production– Aerobic RespirationCellular

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

Why 36-38 ATP?

Electron shuttlesspan membrane

CYTOSOL 2 NADH

2 FADH2

2 NADH 6 NADH 2 FADH22 NADH

Glycolysis

Glucose2

Pyruvate

2AcetylCoA

Citricacidcycle

Oxidativephosphorylation:electron transport

andchemiosmosis

MITOCHONDRION

by substrate-levelphosphorylation

by substrate-levelphosphorylation

by oxidative phosphorylation, dependingon which shuttle transports electronsfrom NADH in cytosol

Maximum per glucose:About

36 or 38 ATP

+ 2 ATP + 2 ATP + about 32 or 34 ATP

or

Figure 9.16