Unit 12: Oxidative Phosphorylation

What do electrons from NADH & FADH₂ move through in oxidative phosphorylation?

4 multienzyme complexes to reduce O₂ to H₂O

What does the electromotive force do?

Moves protons (H+) from mitochondria matrix across inner membrane to intermembrane space

What does the electromotive force create?

Gradient

• Matrix is negative

• Intermembrane space is positive

What does the protomotive force do?

Moves the protons back into matrix through proton channel

What does the protomotive force cause?

ADP to convert to ATP

What are the 2 major electron carriers in oxidative phosphorylation?

• Ubiquinone

  • “Coenzyme Q”

  • Can carry 2 electrons

• Cytochrome c

  • Protein which porphyrin rings bound to central iron atom can change oxidation states

  • Can carry 1 electron

What do the multienzyme complexes do?

All carry out ox/red reactions as electrons are being moved

What complexes does NADH enter?

Complex I, III, & IV

(NOT II)

What complexes does FADH₂ enter?

II, III, & IV

(NOT I)

What happens in complex I?

• NADH → NAD+ (regenerated)

• Electrons are passed to Q (ox) → QH₂ (red)

• 4 protons move across membrane

What happens in complex II?

• FADH₂ → FAD (regenerated)

• Electrons are passed to Q (ox) → QH₂ (red)

• No protons move across membrane

What happens in complex III?

• Electrons move from QH₂ → 2 cytochrome c

• 4 protons are pumped/moved across membrane

What happens in complex IV?

• Electrons move from 2 cytochrome c (red) → oxygen

• H₂O is formed, cytochrome c (ox) are regnerated

• 2 protons move across membrane

What is ATP synthesis catalyzed by?

ATP synthase when 3 protons move across (inward)

Do synthase enzymes require ATP?

No

Do synthetase enzymes require ATP?

Yes

What is F₀?

Proton channel

What is F₁?

Catalytic domain

What does movement of ATP from mitochondrial matrix to cytosol require?

1 additional proton

What is required to synthesize ATP & allow it to be made available?

Inward movement of 4 protons

How many protons to synthesize ATP?

3 H+

What is the purpose of glycerol 3-P shuttle?

• “Bad currency exchange”

• Move NADH made in step 6 of glycolysis into matrix

• NADH exchanges electrons & forms FADH₂

  • 4 less protons are pumped across membrane

What does the Malate-asparate shuttle require?

• 2 reversible reactions

  • Oxaloacetate → Malate

  • Oxaloacetate + Glutamate → Asparate + alpha-ketoglutarate

    • Aminotransferase enzymes required

• Moved NADH into matrix

What is an Aminotransferase reaction?

• Reversible conversion of amino acid to keto acid

• Requires 2 molecules:

  • Pyruvate → oxaloacetate (enzyme carboxylase)

What is a carboxylase reaction?

• Adds carboxylic acid to methyl group

• Requires biotin (prosthetic group bound to Lysine, similar to lipoic acid)

• Seen with pyruvate → oxaloacetate & acetyl CoA → malonyl CoA

What is a lipase reaction?

• Hydrolysis of fatty acid from triacylglycerol