1. How Cells Release Chemical Energy
Chapter 7

2. Impacts, Issues When Mitochondria Spin Their Wheels
Mitochondria are the organelles responsible for releasing the energy stored in foods
In Luft’s syndrome, the mitochondria are active in oxygen consumption, but with little ATP formation to show for it
In Friedreich’s ataxia, too much iron in the mitochondria causes an accumulation of free radicals that attack valuable molecules of life

3. The Impact
Proper, or improper, functioning of mitochondria is the difference between health and disease

4. Overview of Energy-Releasing Pathways
Section 7.1
Overview of
Energy-Releasing Pathways

5. Producing the Universal Currency of Life
All energy-releasing pathways:
require characteristic starting materials
yield predictable products and by-products
produce ATP

6. 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

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

8. 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

9. Energy-Releasing Pathways

10. Overview of Aerobic Respiration
C6H O CO2 + 6H20
glucose oxygen carbon dioxide water

11. Overview of Aerobic Respiration

12. Main Pathways Start with Glycolysis
Glycolysis occurs in cytoplasm
Reactions are catalyzed by enzymes
Glucose 2 Pyruvate
(six carbons) (three carbons)

13. p.106a

14. Three Series of Reactions Are Required for Aerobic Respiration
Glycolysis is the breakdown of glucose to pyruvate
Small amounts of ATP are generated

15. Three Series of Reactions Are Required for Aerobic Respiration
The Krebs cycle degrades pyruvate to CO2 and water;
NAD and FAD accept H+ ions and electrons to be carried to the electron transfer chain
Small amounts of ATP are generated

16. Three Series of Reactions Are Required for Aerobic Respiration
Electron transfer phosphorylation processes the H+ ions and electrons to generate lots of ATP
Oxygen is the final electron acceptor

17. The Role of Coenzymes
NAD+ and FAD accept electrons and hydrogen from intermediates during the first two stages
When reduced, they are NADH and FADH2
In the third stage, these coenzymes deliver the electrons and hydrogen to the transfer chain

18. Overview of Aerobic Respiration

19. The First Stage: Glycolysis
Section 7.2
The First Stage: Glycolysis

20. Glucose
A simple sugar
(C6H12O6)
Atoms held together by covalent bonds

21. Glycolysis Occurs in Two Stages
Energy-requiring steps
ATP energy activates glucose and its six-carbon derivatives

22. Glycolysis Occurs in Two Stages
Energy-releasing steps
The products of the first part are split into 3-carbon pyruvate molecules
ATP and NADH form

23. Energy-Requiring Steps

24. Energy-Releasing Steps
ATP
PGAL
NADH
2 ATP produced
ENERGY -
RELEASING STEPS
OF GLYCOLYSIS
NAD + P i 3
phosphoglycerate 2
PEP
ADP
1,3
bisphosphoglycerate
pyruvate
to second set of reactions
substrate
level
phosphorylation H O

25. Glycolysis in a Nutshell
Glucose is first phosphorylated in energy-requiring steps, then split to form two molecules of PGAL
Enzymes remove H+ and electrons from PGAL to change NAD+ to NADH (which is used later in electron transfer
PGAL is converted eventually to pyruvate
By substrate-level phosphorylation, four ATP are produced

26. Substrate-level What?
Substrate-level phosphorylation means that there is a direct transfer of a phosphate group from the substrate of a reaction to some other molecule – in this case, ADP
Substrate is a reactant in a reaction – the substance being acted upon, for example, by an enzyme

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

28. Second Stage of Aerobic Respiration
Section 7.3
Second Stage of Aerobic Respiration

29. Second-Stage Reactions
Occur in the mitochondria
Pyruvate is broken down to carbon dioxide
More ATP is formed
More coenzymes are reduced

30. Fig. 7-5b, p.112

31. Second Stage of Aerobic Respiration

32. Two Parts of Second Stage
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

33. Preparatory Reactions
pyruvate + coenzyme A + NAD+
acetyl-CoA + NADH + CO2
One of the carbons from pyruvate is released in CO2
Two carbons are attached to coenzyme A and continue on to the Krebs cycle

34. What Is Acetyl-CoA? A two-carbon acetyl group linked to coenzyme A CH3

35. Second Stage of Aerobic Respiration

36. =CoA KREBS CYCLE acetyl-CoA CoA oxaloacetate citrate NAD+ NADH H2O H2O
malate
isocitrate O
NAD+
NADH
FAD
FADH2
fumarate
a-ketoglutarate
succinyl-CoA O
CoA
NAD+
NADH
succinate
ADP + phosphate group
ATP
Stepped Art
Fig. 7-7a, p.113

37. 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

38. 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 is formed
Four-carbon oxaloacetate is regenerated

39. 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. 7-6, p.112

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

41. Third Stage of Aerobic Respiration – The Big Energy Payoff
Section 7.4
Third Stage of Aerobic Respiration – The Big Energy Payoff

42. Electron Transfer Phosphorylation
Occurs in the mitochondria
Coenzymes deliver electrons to electron transfer chains
Electron transfer sets up H+ ion gradients
Flow of H+ down gradients powers ATP formation

43. Electron Transfer Phosphorylation
Electron transfer chains are embedded in inner mitochondrial compartment
NADH and FADH2 give up electrons that they picked up in earlier stages to electron transfer chain
Electrons are transferred through the chain
The final electron acceptor is oxygen

44. Creating an H+ Gradient
OUTER COMPARTMENT
NADH
INNER COMPARTMENT

45. ATP Formation
ATP
INNER
COMPARTMENT
ADP + Pi

46. Summary of Transfers glycolysis e electron transfer phosphorylation
glucose
glycolysis e –
electron
transfer
phosphorylation
2 PGAL 2
pyruvate
2 NADH
2 CO
ATP
2 FADH H +
6 NADH
2 acetyl -
CoA
Krebs
Cycle
4 CO 36
ADP
+ P i

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

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

49. Energy Harvest from Coenzyme Reductions
What are the sources of electrons used to generate the 32 ATP in the final stage?
4 ATP - generated using electrons released during glycolysis and carried by NADH
28 ATP - generated using electrons formed during second-stage reactions and carried by NADH and FADH2

50. 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+

51. Energy Harvest Varies Skeletal muscle and brain cells
Liver, kidney, heart cells
Electrons from first-stage reactions are delivered to NAD+ in mitochondria
Total energy harvest is 38 ATP
Skeletal muscle and brain cells
Electrons from first-stage reactions are delivered to FAD in mitochondria
Total energy harvest is 36 ATP

52. Fermentation Pathways
Section 7.5
Fermentation Pathways

53. Anaerobic Pathways Do not use oxygen
Produce less ATP than aerobic pathways
Two types of fermentation pathways
Alcoholic fermentation
Lactate fermentation

54. 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+

55. Alcoholic Fermentation

56. Yeasts Single-celled fungi Carry out alcoholic fermentation
Saccharomyces cerevisiae
Baker’s yeast
Carbon dioxide makes bread dough rise
Saccharomyces ellipsoideus
Used to make beer and wine

57. Lactate Fermentation

58. Lactate Fermentation 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

59. Lactate Fermentation
Lactobacillus and some other bacteria produce lactate
This produces cheeses, yogurt, buttermilk and other dairy products
Fermenters also are used to cure meats and in pickling
Sauerkraut is an example
Sour taste due to lactic acid (form of lactate)

60. Slow-twitch v. Fast-twitch muscles
Slow-twitch muscles make ATP only by aerobic respiration (no fermentation)
Slow-twitch muscles are for light, steady, prolonged activity
Slow-twitch muscles are red because they have lots of myoglobin, a pigment used to store oxygen
They also have many mitochondria

61. Fast-twitch Muscles
These pale (lighter colored) muscles have few mitochondria and no myoglobin
Fast-twitch muscles, which are used for immediate and intense energy demands, use lactate fermentation to produce ATP
It works quickly, but not for long
Chickens have fast-twitch breast muscles used for quick flights (white meat)
Ducks fly long distances – what color is their breast meat?

62. Alcoholic Fermentation

63. Lactate Fermentation

64. Alternative Energy Sources in the Body
Section 7.6
Alternative Energy Sources
in the Body

65. The Fate of Glucose After eating, glucose is absorbed into the blood
Insulin levels rise, causing greater uptake of glucose by cells
Glycolysis will follow
Excess glucose is converted into glycogen
Glycogen is known as “animal starch,” and is the main storage polysaccharide in animals
Stored in the muscles and the liver

66. Between Meals
When blood levels of glucose decline, pancreas releases glucagon, a hormone
Glucagon stimulates liver cells to convert glycogen back to glucose and to release it to the blood
Glycogen levels are adequate, but can be depleted in 12 hours
(Muscle cells do not release their stored glycogen)

67. Energy Reserves
Glycogen makes up only about 1 percent of the body’s energy reserves
Proteins make up 21 percent of energy reserves
Fat makes up the bulk of reserves (78 percent)

68. Energy from Fats Most stored fats are triglycerides in adipose tissue
Triglycerides are “three-tailed” fats
Triglycerides are broken down to glycerol and fatty acids
Glycerol is converted to PGAL, an intermediate of glycolysis
Fatty acids are broken down and converted to acetyl-CoA, which enters Krebs cycle

69. glycolysis e electron transfer phosphorylation glucose 2 PGAL 2–
electron
transfer
phosphorylation
2 PGAL 2
pyruvate
2 NADH
2 CO
ATP
2 FADH H +
6 NADH
2 acetyl -
CoA
Krebs
Cycle
4 CO 36
ADP
+ P i

70. Energy from Proteins Proteins are broken down to amino acids
Amino acids are broken apart
Amino group is removed, ammonia forms, is converted to urea and excreted
Carbon backbones can enter the Krebs cycle or its preparatory reactions

71. Reaction Sites

72. Section 7.7
Perspective on Life

73. Evolution of Metabolic Pathways
When life originated, atmosphere had little oxygen
Earliest organisms used anaerobic pathways
Later, cyclic pathway (simple form) of photosynthesis increased atmospheric oxygen
Much more efficient cells arose that used oxygen as final acceptor in electron transfer

74. Processes Are Linked Aerobic Respiration Photosynthesis Reactants
Sugar
Oxygen
Products
Carbon dioxide
Water
Photosynthesis
Reactants
Carbon dioxide
Water
Products
Sugar
Oxygen

75. Life Is System of Prolonging Order
Powered by energy inputs from sun, life continues onward through reproduction
Following instructions in DNA, energy and materials can be organized, generation after generation
With death, molecules are released and may be cycled as raw material for next generation