1. Cellular Respiration and Fermentation
Cells break down glucose to produce ATP.
Cellular respiration is aerobic (uses oxygen).
Cellular respiration yields 38 molecules of ATP from every molecule of glucose.
© 2013 Pearson Education, Inc.

2. Cellular Respiration and Fermentation
Cellular respiration occurs in three steps:
Glycolysis
The Krebs cycle
Electron transport
© 2013 Pearson Education, Inc.

3. Cellular Respiration and Fermentation
Glycolysis takes place in the cytoplasm of cells.
The glucose molecule is split into two molecules of pyruvic acid, releasing two molecules of ATP.
© 2013 Pearson Education, Inc.

4. What happens during the process of glycolysis?
Copyright Pearson Prentice Hall

5. Glycolysis
ATP Production
At the beginning of glycolysis, the cell uses up 2 molecules of ATP to start the reaction.
2 ATP
2 ADP
4 ADP
4 ATP
Glycolysis is the first stage in cellular respiration. During glycolysis, glucose is broken down into 2 molecules of pyruvic acid.
Glucose
2 Pyruvic
acid
Copyright Pearson Prentice Hall

6. When glycolysis is complete, 4 ATP molecules have been produced.
2 ADP
4 ADP
4 ATP
Glucose
2 Pyruvic
acid
Copyright Pearson Prentice Hall

7. This gives the cell a net gain of 2 ATP molecules.
Glycolysis
This gives the cell a net gain of 2 ATP molecules.
2 ATP
2 ADP
4 ADP
4 ATP
Glucose
2 Pyruvic
acid
Copyright Pearson Prentice Hall

8. Glycolysis
NADH Production
One reaction of glycolysis removes 4 high-energy electrons, passing them to an electron carrier called NAD+.
2 ATP
2 ADP
4 ADP
4 ATP
Glucose
2NAD+
2 Pyruvic
acid
Copyright Pearson Prentice Hall

9. Glycolysis
Each NAD+ accepts a pair of high-energy electrons and becomes an NADH molecule.
2 ATP
2 ADP
4 ADP
4 ATP
Glucose
2NAD+
2 Pyruvic
acid 2
Copyright Pearson Prentice Hall

10. Glycolysis
The NADH molecule holds the electrons until they can be transferred to other molecules.
2 ATP
2 ADP
4 ADP
4 ATP
2NAD+
2 Pyruvic
acid 2
To the electron transport chain
Copyright Pearson Prentice Hall

11. The Advantages of Glycolysis
The process of glycolysis is so fast that cells can produce thousands of ATP molecules in a few milliseconds.
Glycolysis does not require oxygen.

12. Cellular Respiration and Fermentation
The Krebs cycle occurs in the cell's mitochondria.
In the Krebs cycle, pyruvic acid is converted to acetic acid and bound to a molecule of coenzyme A. The result—acetyl-CoA—is broken down into CO2.
Two molecules of ATP are harvested. Additional energy is stored in the molecules NADH and FADH2.
© 2013 Pearson Education, Inc.

13. What happens during the Krebs cycle?
Copyright Pearson Prentice Hall

14. The Krebs Cycle
During the Krebs cycle, pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions.
Copyright Pearson Prentice Hall

15. The Krebs Cycle
The Krebs cycle begins when pyruvic acid produced by glycolysis enters the mitochondrion.
Copyright Pearson Prentice Hall

16. The Krebs Cycle
One carbon molecule is removed, forming CO2, and electrons are removed, changing NAD+ to NADH.
Copyright Pearson Prentice Hall

17. Coenzyme A joins the 2-carbon molecule, forming acetyl-CoA.
The Krebs Cycle
Coenzyme A joins the 2-carbon molecule, forming acetyl-CoA.
Copyright Pearson Prentice Hall

18. The Krebs Cycle
Acetyl-CoA then adds the 2-carbon acetyl group to a 4-carbon compound, forming citric acid.
Citric acid
Copyright Pearson Prentice Hall

19. The Krebs Cycle
Citric acid is broken down into a 5-carbon compound, then into a 4-carbon compound.
Copyright Pearson Prentice Hall

20. The Krebs Cycle
Two more molecules of CO2 are released and electrons join NAD+ and FAD, forming NADH and FADH2
Copyright Pearson Prentice Hall

21. In addition, one molecule of ATP is generated.
The Krebs Cycle
In addition, one molecule of ATP is generated.
The complete breakdown of glucose through cellular respiration, including glycolysis, results in the production of 36 molecules of ATP.
Copyright Pearson Prentice Hall

22. The energy tally from 1 molecule of pyruvic acid is
The Krebs Cycle
The energy tally from 1 molecule of pyruvic acid is
4 NADH
1 FADH2
1 ATP
Copyright Pearson Prentice Hall

23. Cellular Respiration and Fermentation
In electron transport, electrons carried by NADH and FADH2 are sent down electron transport chains.
In the process, the electrons lose energy, which is used to pump hydrogen ions across a membrane inside the mitochondria.
At the end of the chain, the electrons combine with O2 to make water.
The concentration gradient generated by pumping hydrogen ions is used to make ATP.
© 2013 Pearson Education, Inc.

24. Electron Transport
Electron Transport
The electron transport chain uses the high-energy electrons from the Krebs cycle to convert ADP into ATP.
Copyright Pearson Prentice Hall

25. Electron Transport
High-energy electrons from NADH and FADH2 are passed along the electron transport chain from one carrier protein to the next.
Copyright Pearson Prentice Hall

26. Electron Transport
At the end of the chain, an enzyme combines these electrons with hydrogen ions and oxygen to form water.
Copyright Pearson Prentice Hall

27. Electron Transport
As the final electron acceptor of the electron transport chain, oxygen gets rid of the low-energy electrons and hydrogen ions.
Copyright Pearson Prentice Hall

28. Electron Transport
When 2 high-energy electrons move down the electron transport chain, their energy is used to move hydrogen ions (H+) across the membrane.
Copyright Pearson Prentice Hall

29. Electron Transport
During electron transport, H+ ions build up in the intermembrane space, so it is positively charged.
Copyright Pearson Prentice Hall

30. Electron Transport
The other side of the membrane, from which those H+ ions are taken, is now negatively charged.
Copyright Pearson Prentice Hall

31. Electron Transport
The inner membranes of the mitochondria contain protein spheres called ATP synthases.
ATP synthase
Copyright Pearson Prentice Hall

32. Electron Transport
As H+ ions escape through channels into these proteins, the ATP synthase spins.
Channel
ATP synthase
The electron transport chain uses high-energy electrons from the Krebs cycle to convert ADP to ATP.
Copyright Pearson Prentice Hall

33. Electron Transport
As it rotates, the enzyme grabs a low-energy ADP, attaching a phosphate, forming high-energy ATP.
Channel
ATP synthase
The electron transport chain uses high-energy electrons from the Krebs cycle to convert ADP to ATP.
ATP
Copyright Pearson Prentice Hall

34. The Totals
The Totals
Glycolysis produces just 2 ATP molecules per molecule of glucose.
The complete breakdown of glucose through cellular respiration, including glycolysis, results in the production of 36 molecules of ATP.
Copyright Pearson Prentice Hall

35. The Totals
The complete breakdown of glucose through cellular respiration, including glycolysis, results in the production of 36 molecules of ATP.
Copyright Pearson Prentice Hall

36. Comparing Photosynthesis and Cellular Respiration
The energy flows in photosynthesis and cellular respiration take place in opposite directions.
Copyright Pearson Prentice Hall

37. Comparing Photosynthesis and Cellular Respiration
On a global level, photosynthesis and cellular respiration are also opposites.
Photosynthesis removes carbon dioxide from the atmosphere and cellular respiration puts it back.
Photosynthesis releases oxygen into the atmosphere and cellular respiration uses that oxygen to release energy from food.
Copyright Pearson Prentice Hall

38. Cellular Respiration and Fermentation
In certain cells, under certain conditions, glycolysis is followed by fermentation.
Fermentation uses no oxygen and generates no ATP.
But, fermentation regenerates the molecules necessary to keep glycolysis going, so cells can continue to obtain energy through glycolysis.
Alcoholic fermentation by yeast is used to bake bread and make beer and wine.
Lactic acid fermentation occurs in muscle cells when there is not enough oxygen for cellular respiration to continue. It is also used by red blood cells. Lactic acid fermentation by bacteria and yeast is used to make yogurt and cheese.
© 2013 Pearson Education, Inc.

39. Fermentation
Fermentation
When oxygen is not present, glycolysis is followed by a different pathway. The combined process of this pathway and glycolysis is called fermentation.
Fermentation releases energy from food molecules by producing ATP in the absence of oxygen.
Copyright Pearson Prentice Hall

40. Fermentation does not require oxygen—it is an anaerobic process.
During fermentation, cells convert NADH to NAD+ by passing high-energy electrons back to pyruvic acid.
This action converts NADH back into NAD+, and allows glycolysis to continue producing a steady supply of ATP.
Fermentation does not require oxygen—it is an anaerobic process.
Copyright Pearson Prentice Hall

41. History of Science: Cell Theory
In 1665, Hooke found chambers (actually dried cell walls) in cork and named them cells.
The cell theory states:
All living things are made up of one or more cells.
All cells come from other cells.
© 2013 Pearson Education, Inc.

42. The Discovery of the Cell
The cell theory states:
All living things are composed of cells.
Cells are the basic units of structure and function in living things.
New cells are produced from existing cells.
Copyright Pearson Prentice Hall

43. Math Connection: Why Does Diffusion Limit the Size of Cells?
For a cell with a radius of 1 micrometer,
Surface area πr π(1) π
Volume /3πr /3π(1) /3π
For a cell with a radius of 2 micrometers,
Surface area πr π(2) π(4)
Volume 4/3πr /3π(2) /3π(8)
For a cell with a radius of 3 micrometers,
Surface area πr π(3) π(9)
Volume 4/3πr /3π(3) /3π(27) = = =
= 3 = = =
= 1.5 = = =
= 1
© 2013 Pearson Education, Inc.

44. Science and Society: Stem Cells
Embryonic stem cells come from human embryos that have yet to differentiate into distinct types of cells. These cells have the capacity to develop into all of the kinds of cells in the body.
Although stem cells have great promise for treating many medical conditions, the use of human embryos is controversial.
© 2013 Pearson Education, Inc.