1. PowerLecture: Chapter 8
How Cells Release Stored Energy 1

2. Impacts, Issues: When Mitochondria Spin Their Wheels
More than 100 mitochondrial disorders are known
Friedreich’s ataxia, caused by a mutant gene, results in loss of cordination, weak muscles, and visual problems
Animal, plants, fungus, and most protists depend on structurally sound mitochondria
Defective mitochondria can result in life threatening disorders 2

3. When Mitochondria Spin Their Wheels
Fig. 8-1, p.122 3

4. “Killer” Bees
Descendents of African honeybees that were imported to Brazil in the 1950s
More aggressive, wider-ranging than other honeybees
Africanized bee’s muscle cells have large mitochondria 4

5. ATP Is Universal Energy Source
Photosynthesizers get energy from the sun
Animals get energy second- or third-hand from plants or other organisms
Regardless, the energy is converted to the chemical bond energy of ATP 5

6. Making ATP Plants make ATP during photosynthesis
Cells of all organisms make ATP by breaking down carbohydrates, fats, and protein 6

7. Main Types of Energy-Releasing Pathways
Anaerobic pathways
Evolved first
Don’t require oxygen
Start with glycolysis in cytoplasm
Completed in cytoplasm
Aerobic pathways
Evolved later
Require oxygen
Start with glycolysis in cytoplasm
Completed in mitochondria 7

8. Main Types of Energy-Releasing Pathways
start (glycolysis) in cytoplasm
start (glycolysis) in cytoplasm
completed in cytoplasm
completed in mitochondrion
Anaerobic Energy-Releasing Pathways
Aerobic Respiration
Fig. 8-2, p.124 8

9. Summary Equation for Aerobic Respiration
C6H O CO2 + 6H20
glucose oxygen carbon water
dioxide 9

10. Transfer Phosphorylation Typical Energy Yield: 36 ATP
CYTOPLASM
glucose
ATP 2
ATP 4
Glycolysis
e- + H+
(2 ATP net)
2 NADH
2 pyruvate
Overview of Aerobic Respiration
e- + H+
2 CO2
2 NADH
e- + H+
8 NADH
4 CO2
KrebsCycle
e- + H+ 2
ATP
2 FADH2 e-
Electron
Transfer Phosphorylation 32
ATP H+
water
e- + oxygen
Typical Energy Yield: 36 ATP
Fig. 8-3, p. 135 10

11. The Role of Coenzymes NAD+ and FAD accept electrons and hydrogen
Become NADH and FADH2
Deliver electrons and hydrogen to the electron transfer chain 11

12. Glucose A simple sugar (C6H12O6) Atoms held together by covalent bonds
In-text figure Page 126 12

13. Glycolysis Occurs in Two Stages
Energy-requiring steps
ATP energy activates glucose and its six-carbon derivatives
Energy-releasing steps
The products of the first part are split into three- carbon pyruvate molecules
ATP and NADH form 13

14. Glycolysis glucose to second stage of aerobic
GYCOLYSIS
pyruvate
to second stage of aerobic
respiration or to a different
energy-releasing pathway
GLUCOSE
Fig. 8-4a, p.126 14

15. ENERGY-REQUIRING STEPS fructose–1,6–bisphosphate
Glycolysis
ENERGY-REQUIRING STEPS
OF GLYCOLYSIS
glucose
ATP
2 ATP invested
ADP P
glucose–6–phosphate P
fructose–6–phosphate
ATP
ADP P P
fructose–1,6–bisphosphate
DHAP
Fig. 8-4b, p.127 15

16. ENERGY-RELEASING STEPS 1,3–bisphosphoglycerate 1,3–bisphosphoglycerate
Glycolysis
ENERGY-RELEASING STEPS
OF GLYCOLYSIS P P
PGAL
PGAL
NAD+
NAD+
NADH
NADH Pi Pi P P P P
1,3–bisphosphoglycerate
1,3–bisphosphoglycerate
substrate-level
phsphorylation
ADP
ADP
ATP
ATP
2 ATP invested P P
3–phosphoglycerate
3–phosphoglycerate
Fig. 8-4c, p.127 16

17. Glycolysis P P 2–phosphoglycerate 2–phosphoglycerate H2O H2O P P PEP
substrate-level
phsphorylation
ADP
ADP
ATP
ATP
2 ATP produced
pyruvate
pyruvate
Fig. 8-4d, p.127 17

20. Glycolysis: Net Energy Yield
Energy requiring steps:
2 ATP invested
Energy releasing steps:
2 NADH formed
4 ATP formed
Net yield is 2 ATP and 2 NADH 20

21. Second Stage Reactions
Preparatory reactions
Pyruvate is oxidized into two-carbon acetyl units and carbon dioxide
NAD+ is reduced
Krebs cycle
The acetyl units are oxidized to carbon dioxide
NAD+ and FAD are reduced 21

22. Second Stage Reactions
inner
mitochondrial
membrane
outer
mitochondrial
membrane
inner
compartment
outer
compartment
Fig. 8-6a, p.128 22

23. Preparatory Reactions
pyruvate
coenzyme A (CoA)
NAD+
NADH O O
carbon dioxide
CoA
acetyl-CoA 23

24. The Krebs Cycle Overall Reactants Overall Products Acetyl-CoA 3 NAD+
FAD
ADP and Pi
Overall Products
Coenzyme A
2 CO2
3 NADH
FADH2
ATP 24

25. Preparatory Reactions
Acetyl-CoA
Formation
pyruvate
Preparatory Reactions
coenzyme A
NAD+
(CO2)
NADH
CoA
acetyl-CoA
Krebs Cycle
CoA
oxaloacetate
citrate
NAD+
NADH
NADH
NAD+
FADH2
NAD+
FAD
NADH
ADP +
phosphate
group
ATP
Fig. 8-7a, p.129 25

27. Results of the Second Stage
All of the carbon molecules in pyruvate end up in carbon dioxide
Coenzymes are reduced (they pick up electrons and hydrogen)
One molecule of ATP forms
Four-carbon oxaloacetate regenerates 27

28. Two pyruvates cross the inner mitochondrial membrane.
outer mitochondrial
compartment 2
NADH
inner mitochondrial
compartment 6
NADH
Krebs
Cycle
Eight NADH, two FADH 2, and two ATP are the payoff from the complete break-down of two pyruvates in the second-stage reactions. 2
FADH2
ATP 2
The six carbon atoms from two pyruvates diffuse out
of the mitochondrion, then out of the cell, in six CO
6 CO2
Fig. 8-6b, p.128 28

29. Coenzyme Reductions during First Two Stages
Glycolysis 2 NADH
Preparatory
reactions NADH
Krebs cycle FADH NADH
Total FADH NADH 29

30. Phosphorylation glycolysis e– KREBS CYCLE electron transfer
glucose
Phosphorylation
ATP
2 PGAL
ATP
2 NADH
2 pyruvate
glycolysis
2 FADH2
2 CO2 e–
2 acetyl-CoA
2 NADH H+ H+ 2
6 NADH
KREBS
CYCLE
ATP
Krebs
Cycle
ATP H+
2 FADH2
ATP H+
4 CO2 36
ATP H+ H+
ADP + Pi
electron
transfer
phosphorylation H+ H+ H+
Fig. 8-9, p.131 30

31. Electron Transfer Phosphorylation
Occurs in the mitochondria
Coenzymes deliver electrons to electron transfer chains 31

32. Creating an H+ Gradient
Electron transfer sets up H+ ion gradients
OUTER COMPARTMENT
NADH
INNER COMPARTMENT 32

33. Making ATP: Chemiosmotic Model
Flow of H+ down gradients powers ATP formation
ATP
INNER
COMPARTMENT
ADP + Pi 33

34. Importance of Oxygen
Electron transport phosphorylation requires the presence of oxygen
Oxygen withdraws spent electrons from the electron transfer chain, then combines with H+ to form water 34

35. Anaerobic Pathways Do not use oxygen
Produce less ATP than aerobic pathways
Two types
Fermentation pathways
Anaerobic electron transport 35

36. Fermentation Pathways
Begin with glycolysis
Do not break glucose down completely to carbon dioxide and water
Yield only the 2 ATP from glycolysis
Steps that follow glycolysis serve only to regenerate NAD+ 36

37. Alcoholic Fermentation
glycolysis
C6H12O6
Alcoholic Fermentation 2
ATP
energy input
2 ADP
2 NAD+ 2
NADH 4
ATP
2 pyruvate
energy output
2 ATP net
ethanol formation
2 H2O
2 CO2
2 acetaldehyde
electrons, hydrogen from NADH
2 ethanol
Fig. 8-10d, p.132 37

38. Lactate Fermentation glycolysis C6H12O6 ATP 2 energy input 2 ADP
2 NAD+ 2
NADH 4
ATP
2 pyruvate
energy output
2 ATP net
lactate fermentation
electrons, hydrogen from NADH
2 lactate
Fig. 8-11, p.133 38

39. Anaerobic Electron Transport
Carried out by certain bacteria
Electron transfer chain is in bacterial plasma membrane
Final electron acceptor is compound from environment (such as nitrate), not oxygen
ATP yield is low 39

40. Summary of Energy Harvest (per molecule of glucose)
Glycolysis
2 ATP formed by substrate-level phosphorylation
Krebs cycle and preparatory reactions
Electron transport phosphorylation
32 ATP formed 40

41. Energy Harvest Varies
NADH formed in cytoplasm cannot enter mitochondrion
It delivers electrons to mitochondrial membrane
Membrane proteins shuttle electrons to NAD+ or FAD inside mitochondrion
Electrons given to FAD yield less ATP than those given to NAD+ 41

42. Efficiency of Aerobic Respiration
686 kcal of energy are released
7.5 kcal are conserved in each ATP
When 36 ATP form, 270 kcal (36 X 7.5) are captured in ATP
Efficiency is 270 / 686 X 100 = 39 percent
Most energy is lost as heat 42

43. complex carbohydrates electron transfer phosphorylation
Alternative Energy Sources
FOOD
fats
glycogen
complex carbohydrates
proteins
fatty acids
glycerol
simple sugars
(e.g., glucose)
amino acids
NH3
carbon backbones
glucose-6-phosphate
urea
PGAL 2
ATP
glycolysis 4
ATP
(2 ATP net)
NADH
pyruvate
acetyl-CoA
NADH
CO2
NADH,
FADH2
Krebs
Cycle 2
ATP
CO2 e–
ATP
ATP
electron transfer phosphorylation
ATP
many ATP H+
water
e– + oxygen
Fig. 8-13b, p.135 43

44. Evolution of Metabolic Pathways
When life originated, atmosphere had little oxygen
Earliest organisms used anaerobic pathways
Later, noncyclic pathway of photosynthesis increased atmospheric oxygen
Cells arose that used oxygen as final acceptor in electron transport 44

45. Processes Are Linked
p.136b 45