Chapter 6: How Cells Harvest Energy From Food Pgs Oxidation-Reduction Reactions (Redox Rxns) Warning: Judge carefully what notes to write down!!! Objective: I can identify oxidation and reduction reactions based on what is happening with electrons and atoms, and relate these concepts to cellular respiration

Oxidation Losing an electron = losing energy Electrons carry energy (remember?) Name comes from oxygen (gets e- in end) Oxygen is highly electronegative To gain e-, will oxidize something else Terminology: Atom A undergoes oxidation (A loses e-) Atom A will be oxidized by Atom B Atom B oxidizes Atom A Atom A reduces Atom B

Reduction Gaining an electron = gaining energy Reducing positive charge Where does electron come from? From oxidation Terminology: Atom B undergoes reduction (B gains e-) Atom B will be reduced by Atom A Atom A reduces Atom B (same as before) Atom B oxidizes Atom A (same as before)

Visualizing Terminology (practice) Xe - + Y  X + Ye - Na + Cl ↔ Na + + Cl - *Note Reaction is reversible… X becomes oxidized Y becomes reduced Y oxidizes X X reduces Y Na becomes oxidized Cl becomes reduced Na reduces Cl Cl oxidizes Na Na + becomes reduced Cl - becomes oxidized Na + oxidizes Cl - Cl - reduces Na +

Putting it all together Mnemonic to Remember: OIL RIG = Oxidation Is Loss; Reduction Is Gain The two reactions are (basically) inseparable: Can’t gain e- if something else did not lose (and vice versa) at some point… Loss/gain of electron typically occurs with hydrogen atom (H carrying e-) So, when you see hydrogen loss/gain, can figure out what is reduced/oxidized

Practice NADP +  NADPH Oxidation or Reduction? NADH  NAD+ Oxidation or Reduction? Cellular Respiration C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O + energy Reactant that is oxidized = Reactant that is reduced = Reactant that oxidizes = Reactant that reduces = NADP+ He- NADPH C 6 H 12 O 6 O2O2 O2O2 +

Redox Energetics One reactant gains energy – reduced One reactant loses energy – oxidized How do you know if overall reaction is exergonic or endergonic? Cellular Respiration C 6 H 12 O 6 + 6O 2  6CO 2 + 6H 2 O Photosynthesis 6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6O 2 Methane combustion (burning natural gas) CH 4 + 2O 2  CO 2 + 2H 2 O (Exergonic) (Endergonic) + Energy Energy + + Energy = Exergonic)

Types of Metabolism Anabolism = Builds up (anabolic reactions) This is an endergonic reaction Requires energy Decreases entropy Example: Photosynthesis Catabolism = Breaks down (catabolic rxns) This is an exergonic reaction Releases energy Increases entropy Example: Cellular Respiration DESTROYS BUILDS are as easy to remember as your ABCD’s

Redox w/ Cellular Respiration Cellular Respiration breaks down glucose Glucose is oxidized  loses electrons Release energy in a controlled manner Oxidize glucose little by little Strip electrons a few at a time Use electron carriers (NADH) via ETC Biochemical pathway with several enzymes How many electrons?  If release energy all at once…