1. Biology: Life on Earth Lecture for Chapter 8 Harvesting Energy:
Teresa Audesirk • Gerald Audesirk • Bruce E. Byers
Biology: Life on Earth
Eighth Edition
Lecture for Chapter 8
Harvesting Energy:
Glycolysis and Cellular Respiration
Copyright © 2008 Pearson Prentice Hall, Inc.

2. Chapter 8 Opener
The leg muscles of these racing cyclists require both glucose and oxygen to obtain the energy they need. (inset) Johann Muhlegg is among the elite athletes penalized for artificially boosting the oxygen supply to their cells to increase athletic performance.

3. Chapter 8 Outline 8.1 How Do Cells Obtain Energy? p. 134
8.2 How Is the Energy In Glucose Captured During Glycolysis? p. 135
8.3 How Does Cellular Respiration Capture Additional Glucose Energy From Glucose? p. 138
8.4 Putting It All Together, p. 142

4. Section 8.1 Outline 8.1 How Do Cells Obtain Energy?
Photosynthesis Is the Ultimate Source of Energy
Glucose Is a Key Energy-Storing Molecule
An Overview of Glucose Breakdown

5. Photosynthesis
Photosynthetic organisms capture the energy of sunlight and store it in the form of glucose
The overall equation for photosynthesis is:
6 CO2 + 6H2O  C6H12O6 + 6H2O

6. Glucose Glucose is a key energy-storing molecule:
Nearly all cells metabolize glucose for energy
Glucose metabolism is fairly simple
Other organic molecules are converted to glucose for energy harvesting

7. Glucose
During glucose breakdown, all cells release the solar energy that was originally captured by plants through photosynthesis, and use it to make ATP

8. Overview of Glucose Breakdown
The overall equation for the complete breakdown of glucose is:
C6H12O O2  6CO2 + 6H2O + ATP

9. Overview of Glucose Breakdown
The main stages of glucose metabolism are:
Glycolysis
Cellular respiration

10. FIGURE 8-1 A summary of glucose metabolism

11. Overview of Glucose Breakdown
Glycolysis
Occurs in the cytosol
Does not require oxygen
Breaks glucose into pyruvate
Yields two molecules of ATP per molecule of glucose

12. Overview of Glucose Breakdown
If oxygen is absent fermentation occurs
pyruvate is converted into either lactate, or into ethanol and CO2
If oxygen is present cellular respiration occurs

13. Overview of Glucose Breakdown
Cellular respiration
Occurs in mitochondria (in eukaryotes)
Requires oxygen
Breaks down pyruvate into carbon dioxide and water
Produces an additional 32 or 34 ATP molecules, depending on the cell type

14. Section 8.2 Outline
8.2 How Is the Energy in Glucose Captured During Glycolysis?
Glycolysis Breaks Down Glucose to Pyruvate, Releasing Chemical Energy
In The Absence of Oxygen, Fermentation Follows Glycolysis

15. Glycolysis Overview of the two major phases of glycolysis
Glucose activation phase
Energy harvesting phase

16. FIGURE 8-2 The essentials of glycolysis
(1) Glucose activation: The energy of two ATP molecules is used to convert glucose to the highly reactive fructose bisphosphate, which splits into two reactive molecules of G3P. (2) Energy harvest: The two G3P molecules undergo a series of reactions that generate four ATP and two NADH molecules. Thus, glycolysis results in a net production of two ATP and two NADH molecules per glucose molecule.

17. FIGURE 8-2 (part 1) The essentials of glycolysis
(1) Glucose activation: The energy of two ATP molecules is used to convert glucose to the highly reactive fructose bisphosphate, which splits into two reactive molecules of G3P.

18. FIGURE 8-2 (part 2) The essentials of glycolysis
(2) Energy harvest: The two G3P molecules undergo a series of reactions that generate four ATP and two NADH molecules. Thus, glycolysis results in a net production of two ATP and two NADH molecules per glucose molecule.

19. Glycolysis Glucose activation phase
Glucose molecule converted to highly reactive fructose bisphosphate by two enzyme-catalyzed reactions, using 2 ATPs

20. Glycolysis Energy harvesting phase
Fructose bisphosphate is split into two three-carbon molecules of glyceraldehyde 3-phosphate (G3P)
In a series of reactions, each G3P molecule is converted into a pyruvate, generating two ATPs per conversion, for a total of four ATPs
Because two ATPs were used to activate the glucose molecule there is a net gain of two ATPs per glucose molecule

21. Glycolysis Energy harvesting phase (continued)
As each G3P is converted to pyruvate, two high-energy electrons and a hydrogen ion are added to an “empty” electron-carrier NAD+ to make the high-energy electron-carrier molecule NADH
Because two G3P molecules are produced per glucose molecule, two NADH carrier molecules are formed

22. Glycolysis Summary of glycolysis:
Each molecule of glucose is broken down to two molecules of pyruvate
A net of two ATP molecules and two NADH (high-energy electron carriers) are formed

23. FIGURE 8-2 The essentials of glycolysis
(1) Glucose activation: The energy of two ATP molecules is used to convert glucose to the highly reactive fructose bisphosphate, which splits into two reactive molecules of G3P. (2) Energy harvest: The two G3P molecules undergo a series of reactions that generate four ATP and two NADH molecules. Thus, glycolysis results in a net production of two ATP and two NADH molecules per glucose molecule.

24. Fermentation
Pyruvate is processed differently under aerobic and anaerobic conditions
Under aerobic conditions, the high energy electrons in NADH produced in glycolysis are ferried to ATP-generating reactions in the mitochondria, making NAD+ available to recycle in glycolysis

25. Fermentation
Under anaerobic conditions, pyruvate is converted into lactate or ethanol, a process called fermentation
Fermentation does not produce more ATP, but is necessary to regenerate the high-energy electron carrier molecule NAD+, which must be available for glycolysis to continue

26. Fermentation Some cells ferment pyruvate to form acids
Human muscle cells can perform fermentation
Anaerobic conditions produced when muscles use up O2 faster than it can be delivered (e.g. while sprinting)
Lactate (lactic acid) produced from pyruvate

27. FIGURE 8-4 Glycolysis followed by lactate fermentation

28. FIGURE 8-4 Glycolysis followed by lactate fermentation

29. FIGURE 8-4 Glycolysis followed by lactate fermentation

30. FIGURE 8-3a Fermentation
(a) During a sprint, a runner's respiratory and circulatory systems cannot supply oxygen to her leg muscles fast enough to keep up with the demand for energy, so glycolysis must provide some of the ATP. In muscles, lactic acid fermentation follows glycolysis when oxygen is unavailable.

31. Fermentation
Some microbes ferment pyruvate to other acids (as seen in making of cheese, yogurt, sour cream)
Some microbes perform fermentation exclusively (instead of aerobic respiration)

32. Fermentation
Yeast cells perform alcoholic fermentation

33. FIGURE 8-5 Glycolysis followed by alcoholic fermentation

34. FIGURE 8-5 Glycolysis followed by alcoholic fermentation

35. FIGURE 8-5 Glycolysis followed by alcoholic fermentation

36. Fermentation Glucose is fermented to ethanol and CO2
Sparkling wine is made by adding yeast with the sugar in grapes; CO2 produces the fizz
Bread is made by adding yeast, sugar, and flour; CO2 bubbles cause the dough to rise

37. FIGURE 8-3b Fermentation
(b) Bread rises as CO2 is liberated by fermenting yeast, which converts glucose to ethanol. The dough on the left rose to the level on the right in a few hours.

38. Section 8.3 Outline
8.3 How Does Cellular Respiration Capture Additional Energy from Glucose?
Cellular Respiration in Eukaryotic Cells Occurs in Mitochondria
Pyruvate Is Broken Down in the Mitochondrial Matrix, Releasing More Energy
High-Energy Electrons Travel Through the Electron Transport Chain
Chemiosmosis Captures Energy Stored in a Hydrogen Ion Gradient and Produces ATP

39. Cellular Respiration
In eukaryotic cells, cellular respiration occurs within mitochondria, organelles with two membranes that produce two compartments
The inner membrane encloses a central compartment containing the fluid matrix
The outer membrane surrounds the organelle, producing an intermembrane space

40. FIGURE 8-6 A mitochondrion
The outer and inner mitochondrial membranes enclose two spaces within the mitochondrion.

41. Cellular Respiration Overview of Aerobic Cellular Respiration:
Glucose is first broken down into pyruvate, through glycolysis, in the cell cytoplasm
Pyruvate is transported into the mitochondrion (eukaryotes) and split into CO2 and a 2 carbon acetyl group

42. Cellular Respiration
The acetyl group is further broken down into CO2 in the Krebs Cycle (matrix space) as electron carriers are loaded
Electron carriers loaded up in glycolysis and the Krebs Cycle give up electrons to the electron transport chain (ETC) along the inner mitochondrial membrane

43. Cellular Respiration
A hydrogen ion gradient produced by the ETC is used to make ATP (chemiosmosis)
ATP is transported out of the mitochondrion to provide energy for cellular activities

44. FIGURE 8-6 A mitochondrion
The outer and inner mitochondrial membranes enclose two spaces within the mitochondrion.

45. Pyruvate Breakdown in Mitochondria
After glycolysis, pyruvate diffuses into the mitochondrion into the matrix space
Pyruvate is split into CO2 and a 2-carbon acetyl group, generating 1 NADH per pyruvate

46. Pyruvate Breakdown in Mitochondria
Acetyl group is carried by a helper molecule called Coenzyme A, now called Acetyl CoA
Acetyl CoA enters the Krebs Cycle and is broken down into CO2

47. Pyruvate Breakdown in Mitochondria
Electron carriers NAD+ and FAD are loaded with electrons to produce 3 NADH & 1 FADH2 per Acetyl CoA
6. One ATP also made per Acetyl CoA in the Krebs Cycle
Figure: 19-2 part a
Title:
Viral structure and replication part a
Caption:
(a) A cross section of the virus that causes AIDS. Inside, genetic material is surrounded by a protein coat and molecules of reverse transcriptase, an enzyme that catalyzes the transcription of DNA from the viral RNA template after the virus enters the host cell. This virus is among those that also have an outer envelope that is formed from the host cell's plasma membrane. Spikes made of glycoprotein (protein and carbohydrate) project from the envelope and help the virus attach to its host cell.

48. FIGURE 8-7 The reactions in the mitochondrial matrix
(1) Pyruvate reacts with CoA, forming CO2 and acetyl CoA. During this reaction, an energetic electron is added to NAD+ to form NADH. (2) When acetyl CoA enters the Krebs cycle, coenzyme A is released. The Krebs cycle produces one ATP, three NADH, one FADH2 and two CO2 for each acetyl CoA. Because each glucose molecule yields two pyruvates, the total energy harvest per glucose molecule in the matrix is two ATP, eight NADH, and two FADH2.

49. FIGURE 8-7 The reactions in the mitochondrial matrix
(1) Pyruvate reacts with CoA, forming CO2 and acetyl CoA. During this reaction, an energetic electron is added to NAD+ to form NADH. (2) When acetyl CoA enters the Krebs cycle, coenzyme A is released. The Krebs cycle produces one ATP, three NADH, one FADH2 and two CO2 for each acetyl CoA. Because each glucose molecule yields two pyruvates, the total energy harvest per glucose molecule in the matrix is two ATP, eight NADH, and two FADH2.

50. Electron Transport Chain
Most of the energy in glucose is stored in electron carriers NADH and FADH2
Only 4 total ATP produced per glucose after complete breakdown in the Krebs Cycle

51. Electron Transport Chain
NADH and FADH2 deposit electrons into electron transport chains in the inner mitochondrial membrane
Electrons join with oxygen gas and hydrogen ions to made H2O at the end of the ETCs

52. FIGURE 8-8 The electron transport chain of mitochondria
NADH and FADH2 donate their energetic electrons to the carriers of the transport chain. As the electrons pass through the transport chain, some of their energy is used to pump hydrogen ions from the matrix into the intermembrane space. This creates a hydrogen ion gradient that is used to drive ATP synthesis. At the end of the electron transport chain, the energy-depleted electrons combine with oxygen and hydrogen ions in the matrix to form water.

53. Chemiosmosis
Energy is released from electrons as they are passed down the electron transport chain
Released energy used to pump hydrogen ions across the inner membrane
Hydrogen ions accumulate in intermembrane space

54. Chemiosmosis
Hydrogen ions form a concentration gradient across the membrane, a form of stored energy
Hydrogen ions flow back into the matrix through an ATP synthesizing enzyme
Process is called chemiosmosis

55. Chemiosmosis
Flow of hydrogen ions provides energy to link molecules of ADP with phosphate, forming ATP
ATP then diffuses out of mitochondrion and used for energy-requiring activities in the cell

56. FIGURE 8-8 The electron transport chain of mitochondria
NADH and FADH2 donate their energetic electrons to the carriers of the transport chain. As the electrons pass through the transport chain, some of their energy is used to pump hydrogen ions from the matrix into the intermembrane space. This creates a hydrogen ion gradient that is used to drive ATP synthesis. At the end of the electron transport chain, the energy-depleted electrons combine with oxygen and hydrogen ions in the matrix to form water.

57. Section 8.4 Outline 8.4 Putting It All Together
A Summary of Glucose Breakdown in Eukaryotic Cells
Glycolysis and Cellular Respiration Influence the Way Organisms Function

58. Summary of Glucose Breakdown
Figure 8-9, p. 142, summarizes the process of glucose metabolism in a eukaryotic cell with oxygen present…

59. FIGURE 8-9 A summary of glycolysis and cellular respiration

60. Summary of Glucose Breakdown
Figure 8-10, p. 143, shows the energy produced b each stage of glucose breakdown…

61. FIGURE 8-10 Energy harvest from the breakdown of glucose
Why do we say that glucose breakdown releases "36 or 38 ATP molecules," rather than one specific number? Glycolysis produces two NADH molecules in the cytosol. The electrons from these two NADH molecules must be transported into the matrix before they can enter the electron transport chain. In most eukaryotic cells, the energy of one ATP molecule is used to transport the electrons from each NADH molecule into the matrix. Thus, the two "glycolytic NADH" molecules net only two ATPs, not the usual three, during electron transport. The heart and liver cells of mammals, however, use a different transport mechanism, one that does not consume ATP to transport electrons. In these cells, the two NADH molecules produced during glycolysis net three ATPs each, just as the "mitochondrial NADH" molecules do.

62. Influence on How Organisms Function
Metabolic processes in cells are heavily dependent on ATP generation (cyanide kills by preventing this)
Muscle cells switch between fermentation and aerobic cell respiration depending on O2 availability