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  1. 1. Oxidation-Reduction important reaction type in biochemistry Electron transfer reaction many different types of reactions Oxidation and reduction have to occur simultaneously
  2. 2. Definitions <ul><li>Reduction </li></ul><ul><li>Gaining of electrons </li></ul><ul><li>Loss of oxygen </li></ul><ul><li>Gaining of Hydrogen </li></ul><ul><li>Oxidation </li></ul><ul><li>Loss of electrons </li></ul><ul><li>Gaining of oxygen </li></ul><ul><li>Loss of Hydrogen </li></ul>
  3. 3. Loss of electrons/Gaining of electrons
  4. 4. Loss of electrons/Gaining of electrons <ul><li>Which species is being oxidized? </li></ul><ul><li>Which species is being reduced? </li></ul><ul><li>Importance of this reaction? </li></ul><ul><li>One step in gluconeogenesis (formation of glucose) </li></ul><ul><li>The reverse reaction occurs when vigorously contracting muscles function under low oxygen conditions </li></ul>
  5. 5. Thermodynamics <ul><li>Study of energy </li></ul><ul><li>Important to understanding biochemistry </li></ul><ul><li>Two key terms: </li></ul><ul><li>Enthalpy  H : Heat of reaction at constant pressure </li></ul><ul><li>Endothermic: Require heat  +  H </li></ul><ul><li>Exothermic: Releases heat -  H </li></ul><ul><li>Change in Entropy  S : Change in Randomness </li></ul>
  6. 6. First Law of Thermodynamics <ul><li>Energy is conserved during the course of a chemical change </li></ul><ul><li>Energy can be transformed into one form from another </li></ul><ul><li>Energies: Potential, Kinetic, Light, Heat </li></ul><ul><li>Example: What happens when you dive off a diving board into a pool? </li></ul>
  7. 7. Second Law of Thermodynamics <ul><li> S univ > 0 for a Spontaneous Reaction </li></ul><ul><li>What does this mean? </li></ul><ul><li>Reactions happen without outside intervention when the entropy (randomness) of the universe increases.  S univ is the change in entropy </li></ul>
  8. 8. Spontaneous Reactions <ul><li>Spontaneous Reactions are Thermodynamically Favored Reactions </li></ul><ul><li>Entropy of the universe (  S univ )=entropy of the system + entropy of surroundings </li></ul><ul><li>The change in entropy of univ has to be positive </li></ul><ul><li> S univ > 0 for a spontaneous reaction. </li></ul><ul><li>Note that  S system can be negative if  S surroundings is sufficiently positive to overcome it </li></ul><ul><li>Examples: </li></ul>
  9. 9. Spontaneous Reactions <ul><li>Gibbs-Helmhotz equation describes the second law in terms of Free energy (  G) </li></ul><ul><li>Free energy is derived from the Second Law. It is the same thing using different terms. </li></ul><ul><li>It is the amount of work that the system can do or the amount of work needed for the system </li></ul>
  10. 10. <ul><li>Spontaneous Reactions </li></ul><ul><li>Free energy has to be released from the system if the process is spontaneous </li></ul><ul><li>For a spontaneous process: </li></ul><ul><li> Gsys is negative or  Gsys < 0 </li></ul><ul><li>These reactions are thermodynamically favored </li></ul><ul><li>These reactions are said to be exergonic </li></ul><ul><li>Amount of energy available to do work </li></ul>
  11. 11. Non-Spontaneous Process <ul><li>For a non-spontaneous process: </li></ul><ul><li> S univ < 0 </li></ul><ul><li> Gsys is positive or  Gsys > 0 </li></ul><ul><li>These reactions are not thermodynamically favored </li></ul><ul><li>These reactions are said to be endergonic </li></ul>
  12. 12. Exergonic vs. Endergonic Reactions <ul><li>Products have more energy than reactants </li></ul><ul><li>Energy gained by system </li></ul>
  13. 13. Exergonic v. endergonic reactions <ul><li>Products have less energy than reactants </li></ul><ul><li>Energy released </li></ul><ul><li>Available to do work </li></ul><ul><li>spontaneous </li></ul>
  14. 14. Linking of exergonic to endergonic reactions (reaction coupling) <ul><li>In biochemical systems, an exergonic reaction is used to drive an endergonic one </li></ul><ul><li>In other words, the free energy released in one reaction is used as the free energy needed in another reaction </li></ul><ul><li>Example: cooking food </li></ul><ul><li>Example: Hydrolysis of ATP is used in many reactions to drive another reaction such as formation of macromolecules </li></ul>
  15. 15. The Big Picture Energy Interconversion in Living Organisms What is the relationship between energy, metabolism, heat, and entropy?
  16. 16. The Big Picture Energy Interconversion in Living Organisms <ul><li>There is Potential Energy Stored in Nutrients (animal cell) or Sunlight (plant cell) </li></ul><ul><li>Convert some of this potential energy through chemical transformations in the cell to do work </li></ul><ul><li>Macromolecules within the cell are formed: Entropy is decreased in the system </li></ul><ul><li>However, products of metabolism (CO 2 for example) increase the randomness of the surroundings </li></ul><ul><li>Heat is given off increasing the randomness of the surroundings </li></ul><ul><li>Overall,  S univ >0 </li></ul>