Oxidation to Release…

1. Cellular Respiration Oxidation to Release… Energy

2. Matter is recycled Energy is not (Entropy) Cells use energy for work and growth Chemical products (CO2, H2O) are recycled

3. Concept 9.1: Catabolic pathways yield energy by oxidizing organic fuels

4. Catabolic Pathways and Production of ATP • The breakdown of organic molecules is exergonic • Two methods: • Cellular respiration • Fermentation

5. Catabolic Pathways and ATP • Cellular respiration • Aerobic • Most prevalent and efficient catabolic pathway • Consumes oxygen and organic molecules • Yields ATP (coupled reaction) • Fermentation - partial degradation of sugars • Anaerobic

6. ATP and Cellular Work • Lots of energy in C-H bonds • Carbos are primary source of C-H, but lipids, proteins can be used • Alternative metabolic pathways

7. Redox Reactions: Oxidation and Reduction • Catabolic pathways yield energy due to the transfer of electrons • Redox reactions transfer electrons from one reactant to another • Oxidation - substance loses electrons, (oxidized), gains oxygen • Reduction - substance gains electrons, (reduced), gains hydrogen

8. Methane combustion is a redox reaction

9. Electrons ‘Fall’ During Respiration • From high potential energy to low potential energy

10. Electrons ‘Fall’ Via Steps • Electrons passed to COENZYME first • Nicotinamide adenine dinucleotide (NAD+) • Dehydrogenase removes a pair of hydrogen atoms (2 protons; 2 electrons) from the substrate (sugar)

11. NAD+ • NAD+ keeps the two electrons and 1 hydrogen proton • NADH becomes a ‘taxi’ carrying H and electrons to the ETC

12. Coupled reaction

13. Steps of Respiration 1.Glycolysis 2. Kreb’s Citric Acid Cycle 3. Electron Transport Chain (ETC)

14. Steps of Respiration • Mitochondria = site of Kreb’s and ETC • Formation of acetyl CoA ?

15. Cellular Respiration • What you need to know: • Where does each step take place? • What are the reactants and products? • How is ATP produced? • How does the structure of the mitochondria enable respiration to take place?

16. Acetyl CoA

17. Where Do the Reactions Take Place? • Glycolysis = cytosol • Formation of Acetyl CoA = cytosol/mitochondria • Kreb’s = mitochondrial matrix • ETC = mitochondrial inner membrane (cristae)

19. Glycolysis: ‘Split Sugar’ • In the cytosol • Anaerobic • ATP produced by Substrate-level phosphorylation • Exergonic; captured by ATP and NAD (coupling) • Two major phases • Energy investment phase • Energy payoff phase

20. Substrate-level phosphorylation: Phosphate group is enzymatically transferred to ATP

21. 2 ATP are USED to initiate the reaction (activation energy) 4 ATP are FORMED near the end of glycolysis (coupled reaction)

22. Glucose is phosphorylated

24. Substrate-level phosphorylation

25. S-L phosphorylation

26. Reactants: Glucose; C6H12O6 2ATP 4 ADP + P 2 NAD + H Products: (2) pyruvate 3C Pyruvic acid 4 ATP 2 NADH 2 H2O Glycolysis:

27. Glycolysis

28. Glycolysis • ATP used for work • NADH goes to ETC • H2O = metabolic water (?) • (2) Pyruvate go into mitochondria and formation of Acetyl CoA

29. Concept 9.3: The citric acid cycle completes the energy-yielding oxidation of organic molecules

30. Formation of Acetyl Coenzyme A • Transition between glycolysis (anaerobic) and Kreb’s (aerobic) • Pyruvate enters mitochondrion: • Oxidized to form acetate (2C); 3 enzymes • Multienzyme complex

31. Acetyl CoA • CO2 removed; (1st) • 6C to 4C • NAD reduced to NADH (2x) • Coenzyme A is added to acetate group • Acetyl Coenzyme A

32. Reactants 2 Pyruvate 2 NAD + H Products 2 Acetyl CoA (2C) 2 NADH 2 CO2 Acetyl CoA

33. Acetyl CoA • CO2 is waste • (out of cell) • NADH is transferred to ETC • Acetyl CoA goes into Kreb’s

34. Krebs • Cyclical • Citric acid cycle • Hans Krebs; 1930’s • 2 turns of Krebs for each glucose to be oxidized • Enzymes are in the mitochondrial matrix

35. Acetyl CoA transfers acetate (2C) to OAA (4C) CoA remains present and reusable Water removed and re-added: rearranges the citric acid

36. Isocitrate loses CO2 2H are picked up by NAD

37. aKetoglutarate loses the last CO2 molecule 2 H (electrons and proton) picked up by NAD

38. ATP generated by s-l phosphorylation

39. 2 H picked up by FAD

40. 1 more H picked up by NAD Water added

41. Krebs • Exergonic; 8 steps • Energy used to reduce coenzymes • NAD to NADH • FAD to FADH • 2 ATP produced (substrate-level phosphorylation) • Oxaloacetate is regenerated

42. Reactants: 2 Acetyl (2C) 2 ADP + P 6 NAD + H 2 FAD + H2 Products: 4 CO2 2 ATP; substrate-level phosphorylation 6 NADH 2 FADH2 Krebs

44. Krebs • H is ‘carried’ by NADH/FADH to ETC to generate ATP by… • OXIDATIVE PHOSPHORYLATION • CHEMIOSMOSIS

45. Kreb’s ETC

46. Concept 9.4: During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis • NADH and FADH2 donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation

47. ETC • Most ATP created during ETC; • Oxidative phosphorylation • Energy from Krebs is stored in NADH and FADH2 • Exergonic transfer of electrons to ETC generates 32 ATP

48. ETC • Electron carrier molecules (proteins) are embedded within the inner membrane • Each successive carrier has a higher electronegativity than the previous one • Electrons are ‘pulled’ downhill toOxygen • Strongest electronegativity • Final acceptor (inorganic)

49. Coupled reaction

50. ETC • Ubiquinone = lipid • Prosthetic groups = nonprotein cofactors on the carrier molecules that accept and donate electrons as they are passed down the ETC - FMN, iron/sulfur, hemes • Cytochrome= protein carrier in the ETC with a heme group • Iron transfers electrons • Several different cytochromes (similarity suggests evolution)