Lect13_Redox

Lect13_Redox - Redox Reactions Life is nothing but an...

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1 Redox Reactions ‘Life is nothing but an electron looking for a place to rest.’ Nobel Laureate Albert Szent-György Day 13 1. A high enough kinetic barrier to prevent reaction -- so the fuel can be stored until needed. 2. A low enough barrier that you can somehow get over it when necessary. How can life overcome the kinetic barrier in a variable way? Properties of a good fuel . -- the match (heat, kinetic energy) OR … -- a catalyst (in living systems) The barrier can be overcome by: When a match burns, the released energy • A. Comes mainly from the match • B. Comes mainly from the air • C. Is created by the fire • D. Comes from the energy that you used to strike the match • E. None of the above Review: •H 2 + ½ O 2 Æ H 2 O G = -237 kJ Spontaneous, downhill, exergonic reaction Releases energy, which a cell can capture to do work This reaction can power work within a cell (e.g., formation of organic molecules, movement of materials or the entire cell, etc)
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2 Review: •H 2 + ½ O 2 Æ H 2 O G = -237 kJ Spontaneous, downhill, exergonic reaction But if we mix hydrogen and oxygen gas and wait to see water . . . A measurable amount will not form in our lifetime! Why? • Why won’t a “spontaneous” reaction occur immediately? – A. Chemical bonds in the reactants must be broken – B. New chemical bonds must form – C. A molecule must reach a high energy “transition state” before (A) and (B) can occur Today’s Topics A. What types of fuels / reactions do cells use to obtain energy? An introduction to Electron transfers or Oxidation- reduction chemistry (redox) B. How do cells capture the energy released from fuels and transfer it to drive useful reactions? – (i) Why is an internal electron acceptor useful (NAD)? – (ii) How does ATP capture and release energy? Redox Reactions • AH2 loses electrons (and protons) to become A • B gains electrons (and protons) to form BH2 • At equilibrium, products are strongly favored AH 2 + B BH 2 +A <--- donor acceptor Electrons release energy as they drop into more stable states. The closer to the nucleus, the more stable (less energetic) the electron is.
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3 AH 2 + B BH 2 +A <--- donor acceptor At equilibrium, products are strongly favored. This means that … A. The reaction occurs rapidly B. The reaction is exergonic C. The reaction has a positive G D. The concentration of products = reactants at equilibrium E. At equilibrium, the products are less common than reactants AH 2 + B BH 2 +A <--- donor acceptor At equilibrium, the products are strongly favored EXERGONIC reaction - G Tends to increase entropy (disorder) Much more product than reactant at equilibrium AH2 loses electrons to become A B gains electrons to form BH2
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Lect13_Redox - Redox Reactions Life is nothing but an...

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