1. Intro. To Cellular Respiration and Redox

2. Big Picture Sun gives energy to plants Plants store energy as organic molecules Animals eat plants Energy eventually leaves as heat Chemical elements are recycled

3. Working Together… Photosynthesis Occurs in chloroplasts Uses CO2 and H2O Generates Oxygen and Organic Molecules Cellular Respiration Occurs in mitochondria Uses Oxygen and Organic molecules Generates CO2 and H2O

4. Catabolism 2 Catabolic Pathways: Fermentation – degradation of sugars without O2 Cellular Respiration – degradation of sugars with O2 Cellular Respiration has 3 Key Pathways: Glycolysis, Citric Acid Cycle, and Oxidative Phosphorylation Uses enzymes to break down (catabolize) complex organic molecules (rich in potential energy); some energy is released to do work, the rest is released as heat

5. Overall Reaction Organic compound + Oxygen  Carbon Dioxide + Water + Energy C6H12O6 + O2  CO2 + H2O + ATP and heat Why does this generate energy? Transfer of electrons releases energy stored in organic molecules and helps make ATP

6. Redox Reactions “Oxidation-Reduction Reactions” = REDOX reactions Transfer of one or more electrons from one reactant to another Loss of Electrons = Oxidation Gain of Electrons = Reduction Reducing agent is oxidized (causes the other reactant to be reduced) Oxidizing agent is reduced (causes the other reactant to be oxidized)

7. Respiration C 6 H12O 6 is oxidized and O2 is reduced When C 6 H12O 6 is oxidized, it releases energy and makes it available for ATP synthesis Energy foods (fats and carbs) have lots of electrons associated with Hydrogen, but require enzymes to lower Activation Energy. Organic fuel is oxidized in a series of steps so energy can be harnessed for work

8. Electron Transport Chain Composed of molecules (mostly proteins) embedded in the inner membrane of the mitochondria Breaks the fall of electrons into several energy-releasing steps on their way to Oxygen Electrons are stripped from glucose at key steps and travel with a proton (as a H atom) A coenzyme NAD+ transports H It is an electron acceptor and oxidizing agent Enzymes take 2 H atoms from the sugar to give their electrons and 1 H to NAD+ (the other H+ is released) NAD+ becomes NADH

9. Electron Transport Chain NADH shuttles electrons to the higher-energy end of the chain and at the lower-energy end, Oxygen captures electrons to form H2O Each carrier is more electronegative than the last Summary of e- pathway: Food  NADH  ETC  Oxygen

10. Stages of Cellular Respiration 1. Glycolysis – occurs in the cytosol, breaks down glucose into 2 pyruvate 2. Citric Acid Cycle – occurs in the mitochondrial matrix, oxidizes a derivative of pyruvate into CO2 3. Oxidative Phosphorylation – occurs at the mitochondrion inner membrane, includes ETC and chemiosmosis, produces most of ATP For every glucose molecule, ~38 molecules of ATP are produced

11. Glycolysis “splitting of sugar” Starts with a 6-C sugar breaking into two 3-C sugars Does not require Oxygen Has an “Energy investment phase” and an “Energy payoff phase” Spends 2 ATP… Produces 4 ATP and 2 NADH Net: 2 ATP and 2 NADH