CELLULAR RESPIRATION & FERMENTATION

1. CELLULAR RESPIRATION &FERMENTATION CAMPBELL & REECE CHAPTER 9

2. CATABOLIC PATHWAYS • metabolic pathways that released stored nrg by breaking down complex molecules

3. Fermentation • a catabolic pathway • partial degradation of sugars or other organic fuel • anaerobic • not as efficient as aerobic respiration

4. Cellular Respiration • generally means aerobic • cells mostly use glucose as fuel • energy released: ATP + heat (so is exergonic)

5. Cellular Respiration • nrg released: • ΔG = -686 kcal/mol [2870kJ]

6. How does degradation of glucose yield energy? • answer based on transfer of e- during chemical reactions • moving e- releases nrg stored in organic molecules which is ultimately used to synthesize ATP

7. Redox Reactions

8. Redox Reactions

9. Redox Reactions

10. Redox Reactions are Always Coupled

11. Redox Reactions • substance giving away e- is called the reducing agent • substance taking e- is called the oxidizing agent

12. Redox Reactions • some do not involve complete transfer of e- (as in forming ions)

13. Redox Reactions during Cellular Respiration: Glucose is Oxidized & O2 is Reduced

14. What Organic Molecules Make Great Sources of Fuel? • *generally, organic molecules that have lots of hydrogen make excellent fuels because their bonds are source of “hilltop” e- whose nrg will be released as the e- “fall” down nrg gradient when transferred to O2

15. Cellular Respiration • H is transferred from glucose  O2 • as e- transferred nrg state of e- is lowered • that released nrg is available for ATP synthesis

16. Activation Energy • without EA barrier, glucose or other foods would spontaneously combine with O2 in air • body temperature not high enough to initiate combustion of glucose, enzymes required to lower EA

17. Oxidation Mini-Steps Release nrg slowly • glucose & other molecules are broken down in series of steps (each w/own enzyme) • @ key steps e- are stripped from glucose • each oxidation step involves e- traveling with H atom  NAD+  NADH • oxidized reduced • state state

18. NAD+ / NADH • Nicotinamide Adenine Dinucleotide • derivative of niacin

19. NAD+ / NADH • enzymes called dehydrogenases remove a pair of H atoms (with 2 e-) from substrate (glucose) thereby oxidizing it. • dehydrogenase then delivers the 2 e- along with 1 H (1 proton) to its coenzyme NAD+ • 2nd H+ is released to surroundings

20. NAD+ / NADH • by receiving 2 e- & 1 H+, NAD+ loses its (+) charge • NAD+ most versatile e- acceptor in cellular respiration (used in several redox reactions)

21. NAD+ / NADH • When e- passed from glucose  NAD+ they lose very little of their nrg • cellular respiration uses e- transport chain to break fall of e-  O2 into several nrg-releasing steps

22. Electron Transport Chain • consists of a # of molecules (proteins mostly) in inner membrane of mitochondria & plasma membrane of those prokaryotes that have aerobic respiration • @ “top” of chain NADH carries higher nrg e- removed from glucose   “bottom” of chain lower nrg e- passed to O2

23. Electron Transport Chain • e- transfer from NADH  O2 is exergonic reaction with a free energy change of : -53 kcal/mol (-222 kJ/mol) • instead of releasing all that nrg in 1 explosive step, e- cascade down the chain from 1 carrier molecule to next in series of redox reactions • each carrier is more electronegative than previous molecule

24. Electron Transport Chain • O2 is final e- acceptor because it is the most electronegative • can think of it as O2 pulling e- down the chain in nrg-yielding tumble

25. Electron Transport Chain

26. 3 Stages of Cellular Respiration • Glycolysis • Pyruvate Oxidation & Citric Acid Cycle • Oxidative Phosphorylation • e- transport chain • chemiosmosis

28. GLYCOLYSIS • 2 parts: • Energy Investment Phase • Energy Payoff Phase

29. Glycolysis • anaerobic • in cytoplasm • no CO2 released • uses 2 ATP, makes 4 ATP • 2 NAD+ + 4 e- + 4H+  2 NADH + 2H+ • glucose  2 pyruvate + 2 H2 O

34. Citric Acid Cycle • pyruvate mitochondria via active transport (eukaryotic cells) • pyruvate stays in cytoplasm in prokaryotes that perform aerobic respiration

35. Linking Glycolysis & Citric Acid Cycle • Pyruvate’s carboxyl group (already oxidized so has little chemical nrg) is removed as CO2 • Remaining 2 C fragment is oxidized  acetate (ionized form of acetic acid) with e-  NAD+  NADH • CoA (derived from vit. B) attached via S atom to acetic acid  acetyl CoA

36. Fate of Pyruvate in Mitochondria

37. Pyruvate Enters Mitochondria

38. Citric Acid Cycle • aka: Krebs Cycle • tricarboxylic acid cycle • functions as metabolic furnace that oxidizes organic fuel derived from pyruvate

39. Summary of Krebs Cycle

41. Energy-Rich Molecules Produced in Citric Acid Cycle • for each acetyl group entering cycle: • 3 NAD+  3NADH • 1 FAD + 2 e- + 2H+  1 FADH2 • * 1 GDP + 1ATP  1GTP + 1ADP • * GTP made in many animal cell mitochondria: GTP similar to ATP in structure & function /example of substrate-level phosphorylation

43. Oxidative Phosphorylation • @ end of Citric Acid Cycle only have 4 ATP made (counting glycolysis) • also have NADH & FADH2 (hi nrg e- carriers) which accounts for most of nrg extracted form glucose

44. Electron Transport • collection of molecules embedded in inner membrane of mitochondria (prokaryotes have them embedded in their plasma membrane) • inner membrane has multiple folds allowing for multiple copies of e- transport chain to be working at same time

45. Electron Transport Chain • most of the molecules are proteins, rest are nonprotein components necessary for catalytic functions of certain enzymes • there is a drop in free nrg as e- move thru e- transport chain alternating reduced state  oxidized state

47. Electron Transport Chain Animations • http://www.johnkyrk.com/mitochondrion.html • http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter25/animation__electron_transport_system_and_formation_of_atp__quiz_1_.html • http://www.science.smith.edu/departments/Biology/Bio231/etc.html

48. Electron Transport Chain Animations • http://www.dnatube.com/video/2354/Detailed-ElectronTransport-Chain • http://vcell.ndsu.nodak.edu/animations/etc/movie-flash.htm

49. What does e- transport chain accomplish? • e- transport chain makes no ATP directly • it does break the fall of e- from food to O2 into a series of smaller steps that releases nrg in manageable amts • for every 4 e- 1 O2 + 4 H+  2 H2 O • (O2 is final e- acceptor)

50. Chemiosmosis • inner membrane protein ATP Synthase makes ADP + Pi  ATP using the proton (H+) gradient as nrg source • chemiosmosisis the process in which nrg stored in H+ gradient across membrane is used to drive cellular work (see animations)