Glucose metabolism

• Glycolysis: 2 NADH, 2 ATP (net)

• Pre-TCA cycle: 2 NADH

• TCA cycle: 6 NADH, 2 FADH2, 2 A/GTP

Some ATPBig bonus: NADH, FADH2 →

REDUCING POWER

Energy harvest by respiration

• Carbon-carbon bonds: chemical energy

• NADH, FADH2: energy of oxidation

• Proton gradient: potential energy

• ATP synthesis: useable chemical energy

Reducing power/Energy of oxidation

• Not very user-friendly

• How to harvest the energy?

• Electron transport chain– Change energy of oxidation into potential

energy (H+ gradient)– Change potential energy into chemical energy

(F1Fo ATP synthase)

What is energy of oxidation?• Reducing potentials:

NAD+ + H+ + 2e- → NADH E'° ~ -0.414V

ubiquinone + 2H+ + 2e- → ubiquinol E'° ~ +0.045

Electrons (e-) flow spontaneously from NADH to ubiquinone

NADHubiquinone

(reduced form)(oxidized form)

NADH IS A STRONGER REDUCING AGENT THAN UBIQUINOL

Cataloging the red/ox reactionTransfer of e- from NADH to ubiquinone

NADH → NAD+ + H+ + 2e-

ubiquinone + 2H+ + 2e- → ubiquinol

NADH + ubiquinone + H+ → ubiquinol + NAD+

E'° (V)

+0.414

+0.045

+0.459

*extra energy*not yet useableE'° > 0 ~ G'° < 0

Electrons are passed among redox carriers

NADH→NAD+

FMN (↔FMNH2)

Fe-S Cluster

Ubiquinone (coenzyme Q)

Cytochrome C

O2→H2O

REDUCINGSTRENGTH

Couple energetically favorable reactionsto energetically unfavorable reactionsOverall -G

MATRIXGeneration of NADH

INTERMEMBRANESPACE

Redox energy is transformed into potential energy

MATRIX

INTERMEMBRANESPACE

High pH (lower [H+])Electrically negative

Low pH (higher [H+])Electrically positive

Flow of H+ into the matrixIs energetically favorable 1. Input energy to move H+ out 2. Harvest energy

Mitochondria actually look like the cartoons

http://www.tmd.ac.jp/http://faculty.ircc.edu

Redox energy is transformed into potential energy

Establishment of a chemical and electric gradient across the inner membrane

F1Fo ATP synthaseTransforms potentialEnergy into useableChemical energy

Electron transport between electron carriers occurs in protein complexes within the inner

membrane

Complex I• NADH: Ubiquinone

oxidoreductase – 850kDa, 43 subunits– Converts NADH to NAD+

– e- transferred through complex• FMN, Fe-S clusters

– 4 protons are ‘pumped’ from the matrix into the intermembrane space

– Reduces ubiquinone (Q) to ubiquinol (QH2)

Ubiquinol (reduced coenzyme Q)

Complex III• Coenzyme Q:cytochrome c

oxidoreductase– 250 kDa– 11 subunits– 2 coQ oxidized, one CytC

reduced– e- carriers:

• Hemes, Fe-S clusters– Net 4 H+ pumped to

intermembrane space

Complex III, cont.

Cytochrome C

• Heme group carries electrons

• Loosely associated with membrane

• Shuttles e- from complex III to IV

Complex IV• Cytochrome C oxidase

– 160 kDa– 13 subunits– Reduces oxygen

– ½ O2 + 2H+ + 2e- → H2O

Complex II (Use of FADH2)• Succinate dehydrogenase

– Membrane-bound enzyme in the TCA cycle

– 140 kDa– 4 subunits– FAD, Fe-S clusters carry

electrons– e- transferred ubiquinone(Q)

– QH2 carries e- to complex 3

Electron transport

Overall reaction starting with 2 e- from one NADH

NADH + H+ + ½ O2 → NAD+ + H2O

G'° ~ -220 kJ/mol (of NADH)

-highly favorable-coupled to transport of ~10 H+

against a chemical/electrical gradient

Oxidative phosphorylation

• Involves reduction of O2 to H2O by NADH and FADH2

• ATP synthesized through e- transfers

• Inner mitochondrial membrane– Embedded protein complexes

• Succinate dehydrogenase

– Impermeable to most small molecules (and H+)

• Creation of electrochemical gradients

ATP generation• 2 NADH, 2 ATP from glycolysis (glucose)• 1 NADH from pre-TCA (each pyruvate)

• 3 NADH, FADH2 from TCA (each acetyl CoA)– 2 e- from NADH yields 2.5 ATP*

– 2 e- from FADH2 yields 1.5 ATP