Cellular respiration harvests chemical energy from organic compounds like glucose to produce ATP. It occurs in three main stages: glycolysis, the Krebs cycle in the mitochondria, and the electron transport chain. During these stages, electrons are transferred through electron carriers like NADH and FADH2 to oxygen, releasing energy used to synthesize ATP through oxidative phosphorylation. The overall reaction oxidizes glucose and reduces oxygen to produce carbon dioxide, water, and 38 ATP per glucose molecule. When oxygen is limited, fermentation allows glycolysis to continue by reducing pyruvate to ethanol or lactic acid instead of entering the Krebs cycle.

1. Chapter 9~ Cellular Respiration: Harvesting Chemical Energy

2. Cells need energy to perform cellular work: Growth Metabolism Movement Contraction Cell division Transport

3. Principles of Energy Harvesting Respiration is a Catabolic pathway Organic compounds such as glucose are broken down releasing the energy stored in the chemical bonds

5. Cellular Respiration C 6 H 12 O 6 + 6O 2 ---> 6CO 2 + 6H 2 O + ATP

6. Cellular respiration has 3 components: Glycolysis: occurs in the cytosol; degrades glucose into pyruvate Kreb’s Cycle: occurs in mitochondrial matrix; pyruvate into carbon dioxide Electron Transport Chain: occurs in inner membrane of mitochondrion; electrons passed to oxygen

8. Respiration is a Redox reaction Oxidation-reduction Oxidation is e-loss; reduction is e-gain Reducing agent: e-donor Oxidizing agent: e-acceptor

9. “ Leo says Ger”

10. Na + Cl Na+ + Cl- Sodium is ______________? Chlorine is _____________?

11. Some redox reactions change the degree of sharing between covalent bonds

12. C 6 H 12 O 6 + 6O 2 ---> 6CO 2 + 6H 2 O + ATP

13. Oxidizing agent in respiration NAD+ (nicotinamide adenine dinucleotide) Removes electrons from food (series of reactions) NAD+ is reduced to NADH Enzyme action: dehydrogenase Oxygen is the eventual e- acceptor

15. Glycolysis 1 Glucose 2 pyruvate molecules C 6 2C 3 molecules

16. Energy investment phase : cell uses ATP to phosphorylate fuel Energy payoff phase : ATP is produced by substrate-level phosphorylation and NAD+ is reduced to NADH by food oxidation Net energy yield per glucose molecule : 2 ATP plus 2 NADH; no CO2 is released.

18. Other compounds can be converted to simple sugars and consumed during glycolysis Proteins are hydrolyzed into amino acids Fats are digested into glycerol and fatty acids

19. Krebs Cycle (Citric Acid Cycle) Completes the energy yielding oxidation of organic molecules

20. If molecular oxygen is present……. Each pyruvate is converted into acetyl CoA (begin w/ 2): CO2 is released; NAD+ ---> NADH; coenzyme A (from B vitamin), makes molecule very reactive

21. For each pyruvate that enters: 3 NAD+ reduced to NADH 1 FAD+ reduced to FADH 2 1 ATP molecule

23. Electron Transport Chains Couple electron transport (exergonic) to ATP synthesis (endergonic) Oxygen is the terminal (final) electron receptor, therefore the process produces ATP by “Oxidative Phosphorylation” Produces 32-34 molecules of ATP per molecule of glucose

24. Electron transport chains Involve electron carrier molecules (membrane proteins) Shuttle electrons that release energy used to make ATP Sequence of reactions that prevents energy release in 1 explosive step

26. Electron route: food NADH electron transport chain oxygen

27. Electron transport chain Cytochromes carry electron carrier molecules (NADH & FADH2) down to oxygen Chemiosmosis : energy coupling mechanism ATP synthase : produces ATP by using the H+ gradient (proton-motive force) pumped into the inner membrane space from the electron transport chain; this enzyme harnesses the flow of H+ back into the matrix to phosphorylate ADP to ATP (oxidative phosphorylation)

30. Review: Cellular Respiration Glycolysis: 2 ATP (substrate-level phosphorylation) Kreb’s Cycle: 2 ATP (substrate-level phosphorylation) Electron transport & oxidative phosphorylation: 2 NADH (glycolysis) = 6ATP 2 NADH (acetyl CoA) = 6ATP 6 NADH (Kreb’s) = 18 ATP 2 FADH2 (Kreb’s) = 4 ATP 38 TOTAL ATP/glucose

31. FERMENTATION When oxygen is not available, glycolysis is followed by : Alcohol fermentation pyruvate to ethanol lactic acid fermentation pyruvate to lactate Occurs in muscle of animals when insufficient oxygen is present

32. Fermentation Does not produce any additional ATP Does regenerate oxidized NAD, to keep glycolysis operating