1. Cellular Respiration: Harvesting Chemical Energy
Chapter 9

2. Life Is Work Living cells require energy from outside sources
Plants  E from ?
Animals  E from ?

3. Energy flows into ecosystem as light
Photosynthesis
in chloroplasts
CO2 + H2O
Cellular respiration
in mitochondria
Organic
molecules
+ O2
ATP powers most cellular work
Heat
ATP
ATP powers work
Energy leaves as heat

4. Photosynthesis Cellular respiration Organelle = ?
Generates O2 and organic molecules
Cellular respiration
Uses organic molecules to generate ATP

5. Catabolic Pathway review
Organic molecules have potential (chemical) energy
Exergonic rxns break down organic molecules
 energy (and heat)

6. Cellular Respiration Aerobic respiration Anaerobic respiration Uses O2
ATP produced
Anaerobic respiration
Does not use O2
ATP produced

7. Cellular respiration Glycolysis Anaerobic
Occurs in cytoplasm
Anaerobic
Glucose + 2NAD+ + 2ATP  2 pyruvate+ 2NADH + 4ATP
1 glucose  2 ATP and 2 pyruvate
Glucose oxidized to pyruvate (loses electron)
NAD+ reduced to NADH (gains electron)

8. Glycolysis CYTOSOL Electron donor mitochondrion Electrons carried
Substrate-level
phosphorylation
ATP
Cytosol
Glucose
Pyruvate
Glycolysis
Electrons
carried
via NADH
Electron donor
mitochondrion
CYTOSOL

9. Glycolysis 1. Energy investment phase uses 2 ATP
2. Energy payoff phase 
4 ATP produced
2NAD+ reduced to 2NADH
1 glucose split to 2 pyruvate
Glucose + 2NAD+ + 2ATP  2 pyruvate+ 2NADH + 4ATP

10. Energy investment phase
Glucose
2 ADP + 2 P
2 ATP
used
formed
4 ATP
Energy payoff phase
4 ADP + 4
2 NAD e– + 4 H+
2 NADH
+ 2 H+
2 Pyruvate + 2 H2O
Net
4 ATP formed – 2 ATP used
2 NADH + 2 H+

11. 10 enzymatic steps in glycolysis

12. 2. Citric acid cycle (Krebs cycle)
mt matrix
Matrix is enclosed by the inner membrane
What’s in the matrix?
Enzymes (acetyl CoA)
mtDNA
Ribosomes

13. Citric acid cycle Where did the pyruvate come from?
2Pyruvate + NAD+ + FADH  2ATP + NADH +
FADH2 + CO2 + H2O
Where did the pyruvate come from?
How did it get into the mt matrix?
# ATP generated?
Waste product? Where does it go?
NADH and FADH2 can donate electrons later
What happened to the sugar?
O2?

14. MITCHONDRION Mitochondrion Substrate-level phosphorylation ATP Cytosol
Glucose
Pyruvate
Glycolysis
Electrons
carried
via NADH
Electrons carried
via NADH and
FADH2
Citric
acid
cycle
MITCHONDRION

15. citric acid cycle 1. Convert 2pyruvate to 2acetyl A (before cycle)
Acetyl CoA links glycolysis to cycle

16. Pyruvate diffuses into mt matrix and is converted to acetyl CoA
CYTOSOL
MITOCHONDRION
NAD+
NADH
+ H+ 2 1 3
Pyruvate
Transport protein
CO2
Coenzyme A
Acetyl CoA
Cellular Respiration: Bioflix animation

17. 2. The citric acid cycle

18. 8 enzymatic steps ATP: For each pyruvate? For each glucose?
NAD+
NADH
+ H+
Acetyl CoA
CO2
CoA
Citric
acid
cycle
FADH2
FAD 2 3
3 NAD+
+ 3 H+
ADP + P i
ATP
8 enzymatic steps
ATP:
For each pyruvate?
For each glucose?
For each turn of cycle?

19. Summary of citric acid cycle
Per molecule glucose =2 pyruvate
NADH and FADH 2 electron donors
2 ATP (1 per turn) per glucose
CO 2 produced (2 per turn)  out
mt matrix
BIO 231 TCA cycle animation: Acetyl CoA formation
Text Activity: The Citric Acid Cycle

20. 3. oxidative phosphorylation in mt cristae
Cristae compartmentalize mt inner membrane = more surface area

21. What happens? NADH and FADH 2 donate electrons in the series of steps
Oxygen accepts electrons  water
H+ proton gradient
ADP + P  ATP
34 ATP produced
Add up the ATP yield per glucose:
Glycolysis + Citric acid cycle + Ox Phos =

22. Oxidative phosphorylation:  34 ATP
Mitochondrion
Substrate-level
phosphorylation
ATP
Cytosol
Glucose
Pyruvate
Glycolysis
Electrons
carried
via NADH
Electrons carried
via NADH and
FADH2
Oxidative
Citric
acid
cycle
phosphorylation:
electron transport
and
chemiosmosis

23. Stepwise Energy Harvest via Electron Transport Chain
1. Controlled rxns
Free energy, G
(a) Uncontrolled reaction
H2O
H2 + 1/2 O2
Explosive
release of
heat and light
energy
(b) Cellular respiration
Controlled
energy for
synthesis of
ATP
2 H e–
2 H +
1/2 O2
(from food via NADH)
2 H+
2 e–
Electron transport
chain

24. NADH
NAD+ 2
FADH2
FAD
Multiprotein
complexes
Fe•S
FMN Q 
Cyt b 

Cyt c1
Cyt c
Cyt a
Cyt a3 IV
Free energy (G) relative to O2 (kcal/mol) 50 40 30 20 10
(from NADH
or FADH2)
2 H+ + 1/2 O2
H2O e–
2. electron transport is a fall in energy during each step to control release of fuel energy
FADH2 donates its electrons later – so provides less energy than NADH

25. Electron Transport Chain
powered by redox reactions
Overview: Wiley
Electron Transport: Wiley
Watch the electrons
Prokaryotes carry out electron transport in the plasma membrane.
In mitochondria, the proteins are embedded in the crisate – the folds provide surface area. The proteins are numbered I – IV. There are non-protein prosthetic groups which provide function for enzymes.
BIO 231 Electron transport animation
Watch the electrons

26. In addition to electron transfer…….
3. H+ ions pumped out

27. H+ gradient, a proton force
ET chain e- pumps H+ across mt membrane
H+ gradient drives ATP production
Interactive concepts
Watch the H+ ions

28. Mcgraw hill electron transport
Watch the H+, no audio

29. Chemiosmosis couples energy of electron transport to ATP synthesis

30. ATP synthase H+ ion enters for one turn ADP + P  ATP
INTERMEMBRANE SPACE
Rotor H+
Stator
Internal
rod
Catalytic
knob
ADP + P
ATP i
MITOCHONDRIAL MATRIX
ATP synthase
H+ ion enters for one turn
ADP + P  ATP
Virtual Cell: Electron
Transport Chain animation

31. Electron transport chain 2 H+ + 1/2O2 H2O
Protein complex
of electron
carriers H+
Cyt c Q  
 V
FADH2
FAD
NAD+
NADH
(carrying electrons
from food)
Electron transport chain
2 H+ + 1/2O2
H2O
ADP + P i
Chemiosmosis
Oxidative phosphorylation
ATP synthase
ATP 2 1

32. An Accounting of ATP Production by Cellular Respiration
Most energy:
glucose  NADH  electron transport chain  proton-motive force  ATP
= ~38 ATP total

33. Maximum per glucose:
About
36 or 38 ATP
+ 2 ATP ATP
+ about 32 or 34 ATP
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
Citric
acid
cycle 2
Acetyl
CoA
Glycolysis
Glucose
Pyruvate
2 NADH
6 NADH
2 FADH2
CYTOSOL
Electron shuttles
span membrane or
MITOCHONDRION
Glycolysis Citric Acid Cycle Ox. Phos.
Cytosol mt mt

34. Anaerobic respiration (no O2)

35. Anaerobic respiration (cytoplasm)
Prokaryotes
Eukaryotes
Generate ATP without O2
Glycolysis
Fermentation

36. Fermentation
No electron transport chain
NAD+ reused in glycolysis (way to keep generating ATP without O2)

37. Alcohol fermentation
Pyruvate + NADH  ethanol + NAD+ + CO2
Bacteria
Yeast by humans for:

38. (a) Alcohol fermentation 2
2 ADP + 2 P i
2 ATP
Glucose
Glycolysis
2 Pyruvate
2 NADH
2 NAD+
+ 2 H+
CO2
2 Acetaldehyde
2 Ethanol
(a) Alcohol fermentation 2

39. Lactic acid fermentation
Pyruvate + NADH  lactate + NAD+
Bacteria, fungi in cheese making
Human muscle cells use lactic acid fermentation to generate Pyruvate + NADH  lactate + NAD+
ATP when O2 is low.

40. (b) Lactic acid fermentation
Glucose
2 ADP + 2 P i
2 ATP
Glycolysis
2 NAD+
2 NADH
+ 2 H+
2 Pyruvate
2 Lactate
(b) Lactic acid fermentation

41. Fermentation (no O2) vs. Aerobic Respiration
Both use glycolysis to oxidize glucose (and other organic fuels ) to pyruvate
ATP
Cellular respiration  38 ATP per glucose
Fermentation  2 ATP per glucose

42. Facultative anaerobes
Obligate anaerobes
fermentation
cannot survive in the presence of O2
Ex. clostridium botulinum
Facultative anaerobes
Yeast and many bacteria
can survive using either fermentation or cellular respiration (pyruvate can be used either way)
Ex. E. coli, Streptococcus
In a facultative anaerobe, pyruvate is a fork in the metabolic road that leads to two alternative catabolic routes

43. Facultative anaerobe Glucose Glycolysis CYTOSOL Pyruvate O2 present:
No O2 present:
Fermentation
O2 present:
Aerobic cellular
respiration
MITOCHONDRION
Acetyl CoA
Ethanol or
lactate
Citric
acid
cycle

44. The Evolutionary Significance of Glycolysis
Glycolysis occurs in nearly all organisms
Glycolysis probably evolved in ancient prokaryotes before O2 on planet

45. Glycolysis and the citric acid cycle connect to other metabolic pathways

46. The Versatility of Catabolism
Glycolysis and fuel
Carbohydrates – many accepted
Proteins  amino acids;  glycolysis or the citric acid cycle
Fats  glycerol  glycolysis
Fatty acids  acetyl CoA
An oxidized gram of fat produces >2X ATP as oxidized gram of carbohydrate

47. Citric acid cycle Oxidative phosphorylation
Proteins
Carbohydrates
Amino
acids
Sugars
Fats
Glycerol
Fatty
Glycolysis
Glucose
Glyceraldehyde-3-
Pyruvate P
NH3
Acetyl CoA
Citric
acid
cycle
Oxidative
phosphorylation

48. Fermentation and anaerobic respiration enable cells to produce ATP without the use of oxygen
Most cellular respiration requires O2 to produce ATP
Glycolysis can produce ATP with or without O2 (in aerobic or anaerobic conditions)
In the absence of O2, glycolysis couples with fermentation or anaerobic respiration to produce ATP

49. Regulation of Cellular Respiration via Feedback Mechanisms
Feedback inhibition is the most common mechanism for control
If ATP concentration begins to drop, respiration speeds up; when there is plenty of ATP, respiration slows down
Control of catabolism is based mainly on regulating the activity of enzymes at strategic points in the catabolic pathway

50. Biosynthesis (Anabolic Pathways)
The body uses small molecules to build other substances
These small molecules may come directly from food, from glycolysis, or from the citric acid cycle