1. Chapter 9: Respiration

2. In open systems, cells require E to perform work (chemical, transport, mechanical)
E flows into ecosystem as Sunlight Autotrophs transform it into chemical E O2 released as byproduct Cells use some of chemical E in organic molecules to make ATP E leaves as heat

3. Catabolic Pathway Simpler waste products with less E
Complex organic molecules
Some E used to do work and dissipated as heat

4. Respiration: exergonic (releases E) C6H12O6 + 6O2  6H2O + 6CO2 + ATP (+ heat) Photosynthesis: endergonic (requires E) 6H2O + 6CO2 + Light  C6H12O6 + 6O2

5. Redox Reactions (oxidation-reduction)
oxidation (donor) lose e-
Xe- + Y  X + Ye-
Oxidation = lose e-
Reduction = gain e-
C6H12O O2  6CO2 + 6H2O +
reduction
reduction (acceptor) gain e-
OiLRiG or LeoGer
oxidation
ATP

7. Food (Glucose)  NADH  ETC  O2
Energy Harvest
Energy is released as electrons “fall” from organic molecules to O2
Broken down into steps:
Food (Glucose)  NADH  ETC  O2
Coenzyme NAD+ = electron acceptor
NAD+ picks up 2e- and 2H+  NADH (stores E)
NADH carries electrons to the electron transport chain (ETC)
ETC: transfers e- to O2 to make H2O ; releases energy

8. NAD+ as an electron shuttle

9. Electron Transport Chain

10. Stages of Cellular Respiration
Glycolysis
Pyruvate Oxidation + Citric Acid Cycle (Krebs Cycle)
Oxidative Phosphorylation (electron transport chain (ETC) & chemiosmosis)

11. Overview of Cellular Respiration

12. Stage 1: Glycolysis
Cellular Respiration

13. Glycolysis “sugar splitting”
Believed to be ancient (early prokaryotes - no O2 available)
Occurs in cytosol
Partially oxidizes glucose (6C) to 2 pyruvates (3C)
Net gain: 2 ATP + 2NADH
Also makes 2H2O
No O2 required

14. Glycolysis Stage 1: Energy Investment Stage
Cell uses ATP to phosphorylate compounds of glucose
Stage 2: Energy Payoff Stage
Two 3-C compounds oxidized
For each glucose molecule:
2 Net ATP produced by substrate-level phosphorylation
2 molecules of NAD+  NADH

15. Substrate-Level Phosphorylation
Generate small amount of ATP
Phosphorylation: enzyme transfers a phosphate to other compounds
ADP + Pi  ATP P
compound

17. Glycolysis (Summary) glucose 2 ATP 2 pyruvate 2 NAD+ ADP P
2 NADH + 2H+
2 ATP
2H2O
2 pyruvate
(3-C)
C3H6O3

18. Stage 2: Pyruvate Oxidation + Citric Acid Cycle
Cellular Respiration

19. Mitochondrion Structure
Citric Acid Cycle
(matrix)
ETC
(inner membrane)

21. Pyruvate Oxidation Pyruvate  Acetyl CoA (used to make citrate)
CO2 and NADH produced

22. Citric Acid Cycle (Krebs)
Occurs in mitochondrial matrix
Acetyl CoA  Citrate  released
Net gain: 2 ATP, 6 NADH , 2 FADH2 (electron carrier)
ATP produced by substrate-level phosphorylation
CO2

24. Summary of Citric Acid Cycle

25. Stage 3: Oxidative Phosphorylation
Cellular Respiration

26. Oxidative Phosphorylation
Electron Transport Chain
Chemiosmosis
Occurs in inner membrane of mitochondria
Produces ATP by oxidative phosphorylation via chemiosmosis
H+ ions pumped across inner mitochondrial membrane
H+ diffuse through ATP synthase (ADP  ATP)

27. Electron Transport Chain (ETC)
Collection of molecules embedded in inner membrane of mitochondria
Tightly bound protein + non-protein components
Alternate between reduced/oxidized states as accept/donate e-
Does not make ATP directly
Ease fall of e- from food to O2
2H+ + ½ O2  H2O

28. As electrons move through the ETC, proton pumps move H+ across inner mitochondrial membrane

29. Chemiosmosis: Energy-Coupling Mechanism
Chemiosmosis = H+ gradient across membrane drives cellular work
Proton-motive force: use proton (H+) gradient to perform work
ATP synthase: enzyme that makes ATP
Use E from proton (H+) gradient – flow of H+ back across membrane

30. Chemiosmosis couples the ETC to ATP synthesis

31. ATP yield per molecule of glucose at each stage of cellular respiration

32. Cellular Respiration

33. Final e- acceptors: sulfate (SO4), nitrate, sulfur (produces H2S)
Anaerobic Respiration: generate ATP using other electron acceptors besides O2
Final e- acceptors: sulfate (SO4), nitrate, sulfur (produces H2S)
Eg. Obligate anaerobes: can’t survive in O2
Facultative anaerobes: make ATP by aerobic respiration (with O2 present) or switch to fermentation (no O2 available)
Eg. human muscle cells

34. Fermentation = glycolysis + regeneration of NAD+

35. Glycolysis Fermentation Respiration
Without O2
O2 present
Fermentation
Respiration
Keep glycolysis going by regenerating NAD+
Occurs in cytosol
No oxygen needed
Creates ethanol [+ CO2] or lactate
2 ATP (from glycolysis)
Release E from breakdown of food with O2
Occurs in mitochondria
O2 required (final electron acceptor)
Produces CO2, H2O and up to 32 ATP

36. Types of Fermentation Pyruvate  Ethanol + CO2 Ex. bacteria, yeast
Alcohol fermentation
Lactic acid fermentation
Pyruvate  Ethanol + CO2
Ex. bacteria, yeast
Used in brewing, winemaking, baking
Pyruvate  Lactate
Ex. fungi, bacteria, human muscle cells
Used to make cheese, yogurt, acetone, methanol
Note: Lactate build-up does NOT causes muscle fatigue and pain (old idea)

37. Various sources of fuel
Carbohydrates, fats and proteins can ALL be used as fuel for cellular respiration
Monomers enter glycolysis or citric acid cycle at different points

38. Phosphofructokinase:
Allosteric enzyme that controls rate of glycolysis and citric acid cycle
Inhibited by ATP, citrate
Stimulated by AMP
AMP+ P + P ATP

39. Respiration: Big Picture

40. aerobic cellular respiration
ENERGY
aerobic cellular respiration
(with O2)
anaerobic (without O2)
glycolysis
(cytosol)
mitochondria
Fermentation
(cytosol)
pyruvate oxidation
ethanol + CO2
(yeast, some bacteria)
citric acid cycle
substrate-level phosphorylation
lactic acid
(animals)
ETC
oxidative phosphorylation
chemiosmosis

41. Glycolysis & Citric Acid Cycle

42. Oxidative Phosphorylation
Electron Transport Chain
Chemiosmosis