Biological Membranes and Energy Production

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Biological Membranes and Energy Production
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Membranes as Energy Transducers
Inner leaflet
Outer leaflet
Asymmetry in chemical environments
Integral membrane proteins allow formation of
asymmetrical environments
Membrane Bilayer
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Electrochemical Gradients can provide Energy
The downhill motion of Na to the left provides
a measureable electrical potential (E) across the
membrane once Na ions reach equilibrium
The magnitude of E can be calculated using Nernst
equation
E RT/ZF ln NaL / NaR
This downhill motion of ions can be translated
into free energy change (?G). The movement of
ions across a selectively permeable barrier is
dependent on 1) voltage and 2) concentration
gradient
?GC -RT ln Nain/ Naout
?GM -nFE
Na channel
?G ?GC ?GM
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H gradients provide the energy necessary to
produce ATP
Chemical Energy
Light Energy
Electrical Energy
H gradient
ATP
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H Gradients Perform a Number of Tasks
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Oxidative Phosphorylation
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Electron Transport Chain (ETC)
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Sequence of e- transport

• complex II no ATP
• Inhibitors discovery of complexes

Redox Potential (V)
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Chemiosmotic Theory

• The process of ATP production is catalyzed by a
  H Translocating ATPase
• Termed chemiosmotic theory
• Chemiosmotic theory requires four parameters
• intact mitochondrial membrane
• impermeable to ions that may dissipate the
  electrochemical gradient
• ?G of electron tranport is stored in a proton
  gradient which is used to produce ATP
• The proton gradient can be sequestered, lowering
  ATP production. This event DOES NOT INHIBIT NADH
  OR SUCCINATE OXIDATION

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Complex V is a Multisubunit Protein

• FOF1 ATPase
• Transmembrane protein (450KDa)
• F0 subunit is the transmembrane H channel with 3
  subunits (a8, b1, c2)
• H translocation depends on Glu
• Determined by DCCD inhibition (prevents H
  translocation
• Oligomycin blocks the F0 pump
• F1 subunit is a soluble peripheral protein in the
  matrix
• a3ß3?de subunits
• ß sudunit catalyzes ATP production

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Protons Propel ATP Production
Conformational change in ß subunit
cap
stalk
Rotation of the ? subunit
Membrane spanners
NOTE this ATPase is reversible
3H
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Uncouplers of Oxidative Phosphorylation

1. Synthetic or Exogenous Uncouplers
2. Valinomycin
3. Ionophores
4. Protonophores (2,4-DNP)

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2) Natural Uncouplersthe protein Thermogenin
(UCP) found in brown adipose tissue