Electron Transport

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Electron Transport

• Markus Krummenacker
• Bioinformatics Research Group
• SRI International
• kr_at_ai.sri.com

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What is the Electron Transport System ?

• The overall purpose of the electron transport
  system is to re-generate ATP using energy
  contained in high-energy electrons.
• Gradually extract energy from high-energy
  electrons in a series of redox steps.
• This energy is used to pump protons across the
  membrane, creating an electrochemical gradient.
• The proton gradient drives ATP synthase.
• The electron transport system consists of a
  series of membrane-associated electron carriers
  and membrane-associated enzyme systems.

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Theme Q-Loop

• Membrane-localized quino redox cofactors

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Internal Representation

• ETRs are Composite-Reactions
• Slots similar to pathways refer to sub-reactions
• Involve 2 Redox-Half-Reactions
• RHRs contain explicit electrons, which can not
  occur freely
• Therefore, 2 RHRs are paired up, connected by the
  electrons
• The electrons are not visible outside of the ETR
• The LEFT and RIGHT substrates of the ETR are
  computed from the RHRs
• Additional vectoral proton transport can be added
  as another sub-reaction

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Redox Half Reactions

• They are the building blocks for ETRs
• STD-REDUCTION-POTENTIAL slot, units of V
• Always written in direction
• Ox. e- --gt Red.
• This allows redox potentials to be compared, to
  derive reaction directionality
• Compartments are important, even for PROTON
• Convention e- has no compartment
• Convention Quino factors (in Membrane-Electron-C
  arriers) have no explicit compartment, and are
  always presumed to reside in the membrane

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Reaction Editor Support

• First, the appropriate Redox Half Reactions need
  to be created
• In a second step, an ETR can be constructed by
  selecting
• a Quino Half Reaction
• a Non-Quino Half Reaction
• optionally, a vectoral proton transport reaction