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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