1. Chapter 9: Respiration

2. What you need to know: The summary equation of cellular respiration.
The difference between fermentation and cellular respiration.
The role of glycolysis in oxidizing glucose to two molecules of pyruvate.
The process that brings pyruvate from the cytosol into the mitochondria and introduces it into the citric acid cycle.
How the process of chemiosmosis utilizes the electrons from NADH and FADH2 to produce ATP.

3. 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

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

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

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

8. 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

9. NAD+ as an electron shuttle

10. Electron Transport Chain

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

12. Overview of Cellular Respiration

13. Cellular Respiration
Stage 1: Glycolysis

14. 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

15. 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

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

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

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

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

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

23. 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

25. Summary of Citric Acid Cycle

26. BioVisions at Harvard: The Mitochondria
BioVisions at Harvard: The Mitochondria

27. Stage 3: Oxidative Phosphorylation
Cellular Respiration
Stage 3: Oxidative Phosphorylation

28. 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)

29. 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

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

31. 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

32. Chemiosmosis couples the ETC to ATP synthesis

33. H+ pumped from matrix to intermembrane space
oxidative phosphorylation
uses
generates
chemiosmosis
which couples
proton gradient
ATP
uses E
to produce
called
redox reactions
H+ pumped from matrix to intermembrane space
proton motive force of
ETC
drives
in which H+
e- passed down E levels
through
ATP synthase
to final e- acceptor
O2  H2O

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

35. BioFlix: Cellular Respiration

36. 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

37. Fermentation = glycolysis + regeneration of NAD+

38. 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

39. 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)

40. 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

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

42. Respiration: Big Picture

43. 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

44. Glycolysis & Citric Acid Cycle

45. Oxidative Phosphorylation
Electron Transport Chain
Chemiosmosis