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Energy generation in mitochondria I. The overall scheme is known as the chemiosmotic mechanism: Two questions need to be answered: How does electron transport result in the expulsion of protons? How is the inward flow of protons used to drive ATP synthesis?. Refer to chapter 18, Stryer, 5e.

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slide1

Energy generation in mitochondria I

  • The overall scheme is known as the chemiosmotic mechanism: Two questions need to be answered:
  • How does electron transport result in the expulsion of protons?
  • How is the inward flow of protons used to drive ATP synthesis?

Refer to chapter 18, Stryer, 5e

Lecture 22, Michael Schweizer

slide5

Electron Flow produces heat

All chemical energy from electron transfer converted to heat energy

Bio-wire is the respiratory assembly; electron flow produces ATP

Bio-battery

slide7

Respiratory Chain

Electron transfer from NADH to O2 involves multisubunit inner membranecomplexes I, III & IV, plusCoQ&cyt c. Within each complex, electrons pass sequentially through a series of carriers. Complex II exists attached to flavoprotein enzymes.

CoQ is located in the lipid core of the membrane, and there are CoQ binding sites in protein complexes.

Cytochrome c resides in the intermembrane space. It alternately binds to complex III or IV during e- transfer.

slide8

Vectorial positioned proteins

Proteins in cytoplasm or lumen or organelles are in solution and free-moving

Random orientation of reaction

Proteins in membranes are insoluble and fixed in orientation

Reactions can be directed

Substrates received and products formed vectorially

slide10

Respiratory assembly

  • Located in

plasmamembrane of bacteria

inner mitochondrial membrane

  • Consists of 4 complexes (I to IV)

immobilised multiproteins/cofactors

2 mobile electron shuttles

Ubiquinone (co-enzyme Q) between I/II and III

Cytochrome c between III and IV

  • Accepts

electrons (and H+) from NADH and FADH2 generated

at numerous oxydation steps

  • Donates
  • electrons to terminal acceptor O2
  • electrons to S, NO3- (inorganic respiration), etc

Bio-wire

slide11

Respiratory chain

    • Propel electrons through multi-enzyme complexes
    • Convert released energy (DG) to form a H+-gradient across membrane
    • Establish a H+ cycle back across membrane
    • Use of H+ cycle to drive ADP + Pi ATP
  • Power transmission by proton gradients:
  • Rotate flagella to propel bacterium
  • Active transport of nutrients into cell
  • Heat production
  • =>Proton gradients are a central interconvertible currency of free energy in biological systems