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Flashcards in Mitochondrial Shuttles and ETC Deck (18)
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give a summary of the electron transport

  • Complex I (NADH dehydrogenase) and Complex II (succinate dehydrogenase) can donate electrons to the lipid-mobile electron carrier Coenzyme Q (found within the inner-mitochondrial membrane)
  • CoQ can donate electrons to Complex III (cytochrome reductase)
  • Complex III can donate electrons to the mobile protein cytochrome C (foud within the inner-membrane space)
  • cytochrome C will donate electrons to complex IV (cytochrome oxidase)
  • complex IV will donate electrons to oxygen


name the prosthetic groups of each complex

  • Compex I: FMN (riboflavin derivative)
  • Complex II: FAD (riboflavin derivative)
  • Complex III: heme groups (Fe3+)
  • Complex IV: Cu2+ and heme groups (Fe3+)


where did the NADH electrons come from?

  • NADH oxidized by CoQ at complex I
  • pyruvate dehydrogenase
  • isocitrate dehydrogenase
  • a-KG dehydrogenase
  • malate dehydrogenase


where did the FADH electrons come from?

  • FADH electrons came from succinate dehydrogenase activity 
  • FADH oxidized by CoQ at Complex II


describe the oxidative phosphorylation and the chemiosmotic gradient

  • as electrons flow down the electrochemical potential, protons are pumped into the intramembrane space
  • protons are pumped into intramembrane space at complexes I, III and IV
  • this creates a pH gradient that is relieved by pumping protons back through complex V
    • the energy released in this process is coupled to ATP synthesis from ADP + P


describe the function of rotenone, piericidin A (antibiotic) and the barbituate amytal 

  • inhibit NADH dehydrogenase in complex I


describe the function of antimycin A (antibiotic) 

  • inhibits cytochrome b of cytochrome reductase (complex III)


describe the function of CO, azide, hydrogen sulfide (H2S) and cyanide (CN-)

  • inhibit cytochrome oxidase (complex IV)


describe the function of oligomycin (antibiotic)

  • inhibits ATP synthase


describe the transport of ATP and ADP

  • adenine nucleotide translocase (ANT): unidirectional exchange of ATP for ADP (antiport) 
  • symport of Pi and H+ is electroneutral


name inhibitors of ANT

  • atractyloside: toxic glycoside from plant
    • binds the outward facing (inter-membrane space) portion of the adenosine nucleotide transporter
  • bongkrekic acid: respiratory toxin produced in coconuts
    • binds the inward facing (matrix) portion of the ANT


describe uncouplers of oxidative phosphorylation

  • certain uncouplers (dinitrophenol, DNP), ASA (aspirin), thermogenin, ionophores act by destroying the proton gradient
  • uncouplers decrease ATP synthesis and increase ETC and O2 consumption


describe thermogenin (aka UCP1)

  • uncoupling protein
  • found exclusively in brown adipocytes in mammals
    • found in newborns in neck and upper back
  • the H+ gradient generated from electron transport is uncoupled from ATP synthesis and generates heat
  • this is the physiological function of brown adipose tissue


describe ionophores

  • compounds that make the inner-membrane permeable to compounds that cannot usually cross
  • both uncouplers and ionophores allow for dissipation of the proton gradient


name examples of ionophores

  • gramicidin is a channel forming ionophore 
  • valinomycin is a mobile carrier
    • associated with carrying K+ across bilayers


describe the 2 shuttle mechanisms

  • cells needs a mechanism to shuttle electrons from NADH (from glycolysis in the cytosol) across inner mt membrane
  • 2 shuttle mechanisms:
    • glycerophosphate shuttle results in the synthesis of 2 ATPs per cytosolic NADH oxidized (lower because NADH -> FADH)
    • malate-aspartate shuttle results in the synthesis of 3 ATPs per cytosolic NADH oxidized (higher bc NADH stays as NADH)


describe the malate-aspartate shuttle


describe the glycerophosphate shuttle