OXIDATIVE PHOSPHORYLATION

9/25/07

ATP _ Universal Carrier of Free Energy

_ Chemical_ Ionic

Provides Energy for:_ Mechanical

Work

Role of ATP in Metabolism

Know this structure

It is the most important molecule in biochemistry.

The Concept

Energy rich molecules donateelectrons to specific coenzymesto form energy-rich reducedcoenzymes

1 pair of electrons is donatedper each reduced coenzyme

H2 = H + H

H = 1 electron + 1 proton

:H¯ = 2 electrons + 1 proton

(Hydride ion)+

H+ = 1 proton

These electrons aredonated to the electrontransport chain to formATP

Electrochemical gradient

Oxidized Reduced

Glycolysis

Cytoplasm

Electron Transport

• Inner mitochondrial membrane

• Is the final common pathway by which electrons from food molecules are used to make ATP and molecular oxygen acts as the final acceptor of the electrons

Carriers and transport systemsare used to move ions andmolecules across this membrane

• Membrane convoluted or folded

= ↑ Surface Area

(Cristae)

Contains the ATP Synthetasecomplex

ATP Synthetase complex

50% protein

NADHDehydrogenase

Citric acid cycle

2 e¯

Citric acid cycle 2 e¯

Final acceptor of e-s is molecular oxygen

Cytochrome oxidase(Iron + copper)

Complex V contains ATP Sythase

• Series of Oxidation/Reduction reactions

Electron transport chain ▬ 3 components

• Flavoprotein ▬ NADH Dehydrogenase • CoQ (Quinone) ▬ Ubiquinone • Cytochromes ▬ Heme group ▬ Iron

▬ Ferric (Fe3+) ▬ Ferrous (Fe2+)

Each one of these inhibitors will completely stop electron transportand thus all ATP production

Cyanide

Three Main Tenets of the Mitchell Theory

ATP Synthase

This dissipatesgradient

Blocked by atractyoside(Plant toxin)

FADH2

FAD+

Lower pH

pH gradient

Oligomycinblocks

ADP

ATP

ATP

More protons

Electricalgradient

1 NADH = 3 ATP1 FADH2 = 2 ATP

Chemiosmotic Hypothesis of Electron Transport coupled to ADP Phosphorylation▬ “Mitchell Hypothesis”Features:

• Protons transported from the matrix to the inner mitochondrial space results in an electric gradient and a pH gradient• As the protons flow through the membrane channel back into the matrix they drive ATP synthesis

Occurs with energy utilized by ATP synthaseThis proton transport couples electron transport to oxidative phosphorylation

Cytoplasm

Uncoupling of Oxidative Phosphorylation

Electron Transport

ADP

ATP

ADP

ATP

ADP

ATP

O2

H2O

Electron transport coupled tophosphorylation of ADP ATP

Electron Transport

O2

H2O

+ Dinitrophenol (DNP) breaks down proton gradientHigh doses of aspirin ▬ results in fever

Introduced in 1932 as weight reduction drug= Fatal hyperthermia

Electron transport continues

No ADP phosphorylation

Energy dissipated as heat

HEAT

Brown adipose tissue creates heat by thermogenesis

Thermogenin = uncoupling protein ▬ UCP1

The energy is given offas heat

Mechanism is to↑ FA oxidation whichuncouples oxidationphosphorylation

Breaks down proton gradient

Inherited Diseases of Oxidative Phosphorylation

LIBER’S HEREDITARY OPTIC NEUROPATHY

Bilateral loss of central vision occurs because ofNeuroretinal degeneration

Mutation in mitochondrial DNA

Mitochondrial DNA is maternally inheritedbecause all mitochondria come from the mother

None come from the sperm because none from sperm enter the egg during fertilization

Some mitochondrial myopathies caused bymutations in mtDNA

13 of the ~100 proteins in the mitochondrion arecoded for by mtDNA

Has mutation rate > 10x that of nuclear DNA

Malate-Aspartate shuttle

3 ATP for each NADH

Glycerophosphate shuttle

2 ATP for each NADH transported into mitochondrionfrom the cytoplasm

1

2 3

4

6

75

8

2 Shuttle systems to bring cytosolic NADH intomitochondria for oxidative phosphorylation

1) Glycerophosphate shuttle = 36 ATP

2) Malate-aspartate shuttle = 38 ATP

Count ATPs: Anerobic glycolysis = 2 Glycolysis + CAC + oxidative phosphorylation = 38

NADH FADH2 ATP

1 Glycolysis 2

2 Glycolysis (G-3-P 1,3,BisP) 2 6

3 Pyruvate Acetyl CoA 2 6

4, 5, 6 CAC 6 18

7 CAC-FADH2 2 4

8 CAC – substrate level ATP 2

Total 38

Revolves at 100 Hz (revolutions/s)

This is sufficient to produce a turnover ofThe weight of our body of ATP each day!

ATP synthase:

• 2 Domains

F1

F0

• Rotates in 120° stages

• 100 Hz one complete revolution = 3 ATP

• Need 10 H+

1 ATP = 3.3 H+...