Ch 9 Part 3: E'T'C' Oxidative Phosphorylation

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Ch 9 (Part 3) E.T.C./ Oxidative Phosphorylation
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• ? So far, in glycolysis the Krebs cycle, 1
  glucose molecule has resulted in
• ? 4 ATPs (2 from glycolysis, 2 from Krebs)
• ? 10 NADH (2 from gly., 2 from acetyl-CoA step,
  6 from Krebs Cycle)
• ? 2 FADH2 (from Krebs Cycle)

x2
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• ? Following glycolysis and the Krebs cycle, NADH
  and FADH2 account for most of the energy
  extracted from food
• ? These two electron carriers donate electrons to
  the electron transport chain, which powers ATP
  synthesis via oxidative phosphorylation

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ELECTRON TRANSPORT CHAIN (E.T.C.)

• ? E.T.C. a collection of molecules (mostly
  protein complexes) embedded in the inner membrane
  of mitochondrion (foldings of inner membrane form
  CRISTAE)

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The Pathway of Electron Transport

• ? the groups along the chain alternate between
  reduced oxidized states as they accept and
  donate electrons
• ? each successive group is more electronegative
  than the group before it, so the electrons are
  pulled downhill towards OXYGEN (the final
  electron carrier!)

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NADH
50
FADH2
Multiprotein complexes
I
FAD
40
FMN
II
FeS
FeS
Q
III
Cyt b
Oxidative phosphorylation electron transport and
chemiosmosis
Citric acid cycle
Glycolysis
FeS
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Cyt c1
IV
Free energy (G) relative to O2 (kcal/mol)
Cyt c
ATP
ATP
ATP
Cyt a
Cyt a3
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10
O2
2 H 1/2
0
H2O
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• ? as molecular oxygen (O2) is reduced, it also
  picks up H from the environment to form water
  (H2O)

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ATP Production of the E.T.C.

• Typically, the ATP produced is as follows
• 1 NADH ? 3 ATP
• 1 FADH2 ? 2 ATP
• (FADH2 is dropped off at a lower point in the
  E.T.C., so it generates fewer ATPs)

exchange rate
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Chemiosmosis The Energy-Coupling Mechanism

• ? Electron transfer in the electron transport
  chain causes proteins to pump H from the
  mitochondrial matrix to the intermembrane space
  (active transport)
• ? H (protons) then move back across the
  membrane, passing through channels in ATP synthase

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Chemiosmosis The Energy-Coupling Mechanism

• ? ATP synthase uses the exergonic flow of H to
  drive phosphorylation of ATP
• ? This is an example of CHEMIOSMOSIS, the use of
  energy in a H gradient to drive cellular work

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• ? The energy stored in a H gradient across a
  membrane couples the redox reactions of the
  electron transport chain to ATP synthesis
• ? The H gradient is referred to as a
  PROTON-MOTIVE FORCE, emphasizing its capacity to
  do work

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(inner matrix)
? protons then diffuse back across the membrane
through the ATP synthase complex which causes
the phosphorylation of ADP to form ATP!
(intermembrane space)
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INTERMEMBRANE SPACE
A rotor within the membrane spins as shown when
H flows past it down the H gradient.
H
H
H
H
H
H
H
A stator anchored in the membrane holds the knob
stationary.
A rod (or stalk) extending into the knob also
spins, activating catalytic sites in the knob.
H
Three catalytic sites in the stationary knob join
inorganic phosphate to ADP to make ATP.
ADP

ATP
P
i
MITOCHONDRAL MATRIX
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Inner mitochondrial membrane
Oxidative phosphorylation electron transport and
chemiosmosis
Citric acid cycle
Glycolysis
ATP
ATP
ATP
H
H
H
H
Cyt c
Protein complex of electron carriers
Intermembrane space
Q
IV
III
I
ATP synthase
II
Inner mitochondrial membrane
H2O
2H 1/2 O2
FADH2
FAD
NAD
H
NADH
ADP
ATP
P
i
(carrying electrons from food)
H
Mitochondrial matrix
Electron transport chain Electron transport and
pumping of protons (H), Which create an H
gradient across the membrane
Chemiosmosis ATP synthesis powered by the flow of
H back across the membrane
Oxidative phosphorylation
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ELECTRON TRANSPORT CHAIN ANIMATION!
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SUMMARY

• ? most energy flows in this sequence
• Glucose ? NADH ? E.T.C. ? proton ? ATP
• 
  motive
• 
  force

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• ? approximately 40 of energy in glucose is
  converted to ATP
• ? the remaining energy is lost as heat

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Electron shuttles span membrane
MITOCHONDRION
CYTOSOL
2 NADH
or
2 FADH2
2 FADH2
2 NADH
6 NADH
2 NADH
Oxidative phosphorylation electron
transport and chemiosmosis
Glycolysis
2 Acetyl CoA
Citric acid cycle
2 Pyruvate
Glucose
2 ATP
2 ATP
about 32 or 34 ATP
by substrate-level phosphorylation
by substrate-level phosphorylation
by oxidation phosphorylation, depending on which
shuttle transports electrons form NADH in cytosol
About 36 or 38 ATP
Maximum per glucose