BIOC 460 - DR. TISCHLER

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BIOC 460 - DR. TISCHLER LECTURE 29
OXIDATION PHOSPHORYLATION-2
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OBJECTIVES

1. How pH and charge gradients form across
   mitochondrial inner membrane
2. Electroneutral vs electrogenic transport
   significance of electrogenic transport for
   adenine nucleotide transporter role of this
   transporter.
3. Chemiosmotic model.
4. Components of the ATP synthase complex
   describe their roles.
5. How the malate-aspartate and ?-glycerol
   phosphate electron shuttles generate energy from
   NADH produced by glycolysis.
6. Define respiratory control and uncoupling
   physiological importance of these processes.

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High H
High H






H
-
-
-
-
Inner Membrane
-
-
-
-
-
_
-
Low H
_
Intermembrane Space

Matrix


H





Cytoplasm



H
H
Figure 1. Generation of a pH gradient (H) and
charge difference (negative in the matrix) across
the inner membrane constitute the protonmotive
force that can be used to drive ATP synthesis and
transport processes
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MITOCHONDRIAL TRANSPORT SYSTEMS
Examples of Electroneutral Transport Pyruvate1-
moves into matrix and OH1- moves out Phosphate1-
moves into matrix and OH1- moves out Citrate3-
H exchanges with malate2-
Adenine nucleotide transporter

Figure 2. Electrogenic transport system in
mitochondria.
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INTERMEMBRANE SPACE
ATP4-
OH-
ADP3-
ADP3-
4H
ATP4-
OH-
ADP3-
ADP3-
complex I
NADH H
FMNH2
e-
4H
ATP4-
OH-
e-
ADP3-
e-
ADP3-
inner membrane
e-
3H
ATP4-
CoQ
Pi-
ADP3-
ADP3-
complex III
4H
2H
e-
cyt b
e-
2H
C1
F1
½O2
e-
cyt
MATRIX
C
e-
a-a3
e-
stalk
e-
4H
Fo
complex IV
Proton gradient/ Charge gradient
3H
Figure 3. Oxidative Phosphorylation
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FEATURES OF THE CHEMIOSMOTIC MODEL

• mitochondrial inner membrane is impermeable to
  protons by simple diffusion
• measurable proton (pH) gradient exists across
  the inner membrane
• collapse of the proton gradient (uncoupling)
  abolishes ATP synthesis but accelerates O2
  consumption
• inhibition of the respiratory chain prevents
  ATP synthesis because pumping of protons ceases

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e? electrons
INNER MEMBRANE
OUTER MEMBRANE
CYTOPLASM
MATRIX
Figure 4. The malate-aspartate shuttle.
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e? electrons
INNER MEMBRANE
OUTER MEMBRANE
CYTOPLASM
MATRIX
DHAP
Glycerol-3-phosphate dehydrogenase
(2)
FAD
Figure 5. Glycerol phosphate shuttle.
Cytoplasmic glycerol 3-phosphate dehydrogenase
(1) oxidizes NADH. Glycerol 3-phosphate
dehydrogenase in the inner membrane (2) reduces
FAD to FADH2.
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RESPIRATORY CONTROL

• depends on the availability of ADP
• increased ADP in matrix opens proton channel
• protons move through channel down pH gradient
• respiration increases to compensate for decline
  in pH gradient oxygen consumption (respiration)
  controlled
• at low ADP, ATP synthesis ceases, pH gradient
  builds up, oxygen use diminishes
• as ATP needs rise (i.e., ADP increases)
  respiration is again accelerated
• inhibition of respiratory chain causes loss of
  control

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UNCOUPLER EFFECTS

• hydrophobic molecules that bind protons
• take protons into matrix to collapse pH
  gradient
• without pH gradient, synthesis of ATP ceases
• electron transport chain operates at high rate
  protons are pumped out rapidly in attempt to
  restore pH gradient
• energy is released as heat and the body
  temperature rises
• respiratory control is lost
• uncoupled brown fat mitochondria generates body
  heat in infants until shivering reflex develops