Glucose metabolism Some ATP Big bonus: NADH, FADH2 → REDUCING POWER Glycolysis: 2 NADH, 2 ATP (net) Pre-TCA cycle: 2 NADH TCA cycle: 6 NADH, 2 FADH2, 2 A/GTP Some ATP Big 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 NADH IS A STRONGER REDUCING AGENT THAN UBIQUINOL ubiquinone NADH (oxidized form) (reduced form)

Cataloging the red/ox reaction Transfer of e- from NADH to ubiquinone E'° (V) NADH → NAD+ + H+ + 2e- +0.414 ubiquinone + 2H+ + 2e- → ubiquinol +0.045 NADH + ubiquinone + H+ → ubiquinol + NAD+ +0.459 *extra energy* not yet useable DE'° > 0 ~ DG'° < 0

Electrons are passed among redox carriers REDUCING STRENGTH NADH→NAD+ FMN (↔FMNH2) Fe-S Cluster Ubiquinone (coenzyme Q) Cytochrome C Couple energetically favorable reactions to energetically unfavorable reactions Overall -DG O2→H2O

Redox energy is transformed into potential energy MATRIX Generation of NADH INTERMEMBRANE SPACE

INTERMEMBRANE SPACE MATRIX Flow of H+ into the matrix Is energetically favorable 1. Input energy to move H+ out 2. Harvest energy INTERMEMBRANE SPACE Low pH (higher [H+]) Electrically positive MATRIX High pH (lower [H+]) Electrically negative

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 synthase Transforms potential Energy into useable Chemical 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 DG'° ~ -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