Cellular Respiration & Fermentation

1. Cellular Respiration & Fermentation 9.1-9.6

2. Learning Objectives 2.1 The student is able to explain how biological systems use free energy based on empirical data that all organisms require constant energy input to maintain organization, to grow and to reproduce. [SP 6.2] 2.2 The student is able to justify a scientific claim that free energy is required for living systems to maintain organization, to grow or to reproduce, but that multiple strategies exist in different living systems. [SP 6.1] 2.3 The student is able to predict how changes in free energy availability affect organisms, populations and ecosystems. [SP 6.4] 2.4 The student is able to use representations to pose scientific questions about what mechanisms and structural features allow organisms to capture, store and use free energy. [SP 1.4, 3.1] 2.5 The student is able to construct explanations of the mechanisms and structural features of cells that allow organisms to capture, store or use free energy. [SP 6.2] Text: 9.1-9.5

3. Metabolism Overview 9.1

5. Three Pathways for Producing ATP • Aerobic respiration • Anaerobic respiration • Fermentation

6. Catabolic Pathways • Break down larger molecules and release stored energy • Fermentation: partial degradation of sugars • Occurs in the absence of O2 • aka Anaerobic Respiration • Cellular respiration: more efficient degradation of sugars • Occurs in the presence of O2 • aka Aerobic Respiration

7. Redox Reactions • Reactions in which one or more electrons is transferred • Reduction: gaining an electron • Oxidation: losing an electron • Dehydrogenations: When the electron is lost accompanied by a proton (H+ is lost)

8. Examples of Redox Reactions NAD+is an electron carrier. -NAD accepts 2 electrons and 1 proton to become NADH -the reaction is reversible

11. Electron Transport Chains • Controlled release of energy

12. Oxidative Phosphorylation • Production of ATP using energy derived from the redox reactions of an ETC

13. Substrate Level Phosphorylation • Formation of ATP by direct transfer of a phosphate group to ADP from a catabolic intermediate

14. A closer view

15. Oxidative Cellular Respiration 9.2-9.3

16. The Goal • Maximize ATP production The Method • Slowly release the stored energy • Use electron carriers (trucks) • Convert electron energy to ATP

17. Overview of Cellular Respiration

18. Three Stages • Glycolysis (teal) • Pyruvate oxidation and citric acid cycle (salmon) • Oxidative phosphorylation (violet)

19. Respiration C6H12O6 + 6O2 6CO2 + 6H2O DG = -686kcal/mol of glucose DG can be even higher than this in a cell This large amount of energy must be released in small steps rather than all at once.

20. Glycolysis • Sugar cutting • Two phases • Energy investment phase (5 steps) • Energy payoff phase (5 steps) • Occurs in cytosol

21. Investment Payoff • 1 Glucose • 2 ATP • 2 ADP • 2 NAD+ • 2 Pyruvate • 4 ATP • 2 NADH

22. Pyruvate Oxidation & Citrus Acid Cycle

23. Pyruvate Enters Mitochondrion • Via active transport

24. Pyruvate is Broken Down and Converted to Acetyl-CoA • Occurs in the matrix • Three steps • COO- on carboxyl is removed and given off as CO2 • acetate forms from remaining carbons • NAD+ is reduced forming NADH • Coenzyme A is attached

25. Citric Acid Cycle or Krebs Cycle • Occurs in matrix • Three stages • Acetyl-CoA enters the cycle • Oxidation reactions produce NADH (and FADH2)and CO2 • Minimal ATP is also produced via substrate level phosphorylation • Starting product are regenerated

27. Krebs Summary (One Rotation) Enters Exits • 1 acetyl CoA • 3 NAD+ • 1 ADP • 1 FAD • 1 CoA • 3 NADH • 1 ATP • 1 FADH2 • 2 CO2

28. Oxidative Phosphorylation 9.4

29. Oxidative phosphorylation (Electron Transport & Chemiosmosis) • Series of protein complexes embedded in the mitochondrial inner membrane remove high energy electrons from NADH and FADH2 • Each protein complex transfers the electrons to the next protein complex • Protons accumulate in the intermembrane space from the breakdown of acetyl-CoA building a concentration gradient • Protons are pushed into the intermembrane space utilizing energy lost in the transfer of electrons • Oxygen is used to remove the now low energy electrons

30. Electron Transport and Chemiosmosis

31. ATP Synthase aka Chemiosmosis • Proton gradient is used to drive ATP production

32. Phosphorylation In Out • NADH • FADH2 • O2 • ADP • Phosphate • Kinetic energy • NAD+ • FAD • Proton gradient (“Proton-motive force”) • H2O • ATP (chemical energy)

34. Energy Yield • Theoretical • Prokaryotes- 38 ATP • Eukaryotes 36 ATP • Actual • Eukaryotes- 30 ATP (average)

36. Regulation of Respiration Regulation of aerobic respiration is by feedback inhibition. -a step within glycolysis is allosterically inhibited by ATP and by citrate -high levels of NADH inhibit pyruvate dehydrogenase -high levels of ATP inhibit citrate synthetase

37. Fermentation & Anaerobic Respiration 9.5

38. When there is NO O2 Fermentation Anaerobic Respiration • Does not use ETC • Regenerates NAD+ from NADH • Utilizes an ETC • Prokaryotic • Final electron acceptor may be: • Nitrate • Sulfate • Fumarate • Etc

39. Anaerobic Respiration • Obligate anaerobes: cannot survive in the presence of O2 • Facultative anaerobes: can produce sufficient ATP in absence of O2 for survival • Tend to use aerobic pathways if possible

40. Types of Fermentation Lactic Acid Alcoholic/Ethanol • Occurs in animals • Pyruvate reduced directly by NADH to form lactate • Occurs in yeast and bacterial • Pyruvate converted to ethanol in two steps • Carbon dioxide is removed to form acetaldehyde • Acetaldehyde is reduced by NADH to ethanol

42. Glycolysis and Evolution • Evidence for the early evolution of glycolysis • Almost all organisms use it • It occurs in the absence of oxygen • O2 was not present in any quantity when life evolved • Occurs in cytosol • Does not require specialized structures

43. Other Metabolic Pathways

44. Fats, Proteins, and Other Carbohydrates • Non-glucose molecules are broken down for energy • Many of the products of the early breakdown are intermediates in either glycolysis or the citric acid cycle

46. Poisons Often Interfere with Respiration