1. Why cellular respiration?
Cells carry out the reactions of cellular respiration in order to produce ATP. ATP is used by the cells for energy.
All organisms need energy, therefore all organisms carry out cellular respiration.
The energy needed to produce ATP comes from glucose. Glucose is produced by photosynthesis.
The equation for cellular respiration is: C6H12O6 + 6O2  6CO2 + 6H2O + 36 ATP Notice that it is the reverse of the equation for photosynthesis.

2. Overview of Cellular Respiration
Glucose
glycolysis
2 ATP
2 Pyruvate
Overview of Cellular Respiration
The first step is called glycolysis. It occurs in the cytosol.
During glycolysis, a glucose molecule (6 carbons) is converted to two pyruvate molecules (3 carbons each).
It does not require oxygen (it is anaerobic).
A total of 2 ATP are gained as a result of these reactions.
Details of these reactions will be discussed later.
Glycolysis 6

3. Aerobic respiration occurs in the mitochondrion.
Glucose
2 ATP
2 Pyruvate
34 more
ATP
Oxygen
Aerobic respiration occurs in the mitochondrion.
It requires oxygen (it is aerobic).
It produces an additional 34 ATP.
Aerobic Respiration
Aerobic respiration 7

4. Fermentation occurs if there is no oxygen present.
Glucose
2 ATP
2 Pyruvate
34 more
ATP
0 ATP
Oxygen
No oxygen
Aerobic respiration
Fermentation
Fermentation occurs if there is no oxygen present.
It does not produce additional ATP.
Fermentation
Alcohol + CO2
(yeast, plants)
Lactate
(animals) 9

5. The waste products of fermentation are alcohol or lactate.
Glucose
2 ATP
2 Pyruvate
34 more
ATP
0 ATP
Oxygen
No oxygen
Aerobic respiration
Fermentation
The waste products of fermentation are alcohol or lactate.
Fermentation
Alcohol + CO2
(yeast, plants)
Lactate
(animals) 9

6. Glycolysis glucose (C6) 2C3
Glycolysis consists of a number of different reactions that produce 2 pyruvate molecules from one glucose molecule.
2 pyruvate (C3) 10

7. Glycolysis glucose (C6)
Several different 3-carbon compounds are produced during the reactions. The designation “C3” is used here to represent all of them. Be aware that in addition to carbon, these compounds also contain oxygen and hydrogen.
2C3
2 pyruvate (C3) 10

8. Glycolysis glucose (C6) 2 ATP 2 ADP
Two ATP are consumed during glycolysis.
P-C6-P
This results in a 6-carbon compound that has 2 phosphate groups.
2C3
2 pyruvate (C3) 11

9. Glycolysis glucose (C6) 2 ATP 2 ADP P-C6-P
The 6-carbon compound is split into two 3-carbon compounds. Each of these 3-carbon compounds has one phosphate group.
2 C3-P
2 pyruvate (C3) 11

10. Glycolysis glucose (C6) 2 ATP 2 ADP P-C6-P 2 C3-P 2 NAD+
NAD+ picks up two electrons to become NADH.
2 NADH
2 pyruvate (C3) 14

11. Glycolysis glucose (C6) 2 ATP 2 ADP P-C6-P
The goal of cellular respiration is to produce ATP. NADH contains energy that can be used to produce ATP. This will be discussed later.
2 C3-P
2 NAD+
2 NADH
2 pyruvate (C3) 14

12. Glycolysis glucose (C6) 2 ATP 2 ADP P-C6-P 2 C3-P 2 NAD+ 2 NADH
Additional phosphorylation also occurs, producing 3-carbon compounds that have 2 phosphate groups each.
2 pyruvate (C3) 14

13. Glycolysis glucose (C6) 2 ATP 2 ADP P-C6-P 2 C3-P 2 NAD+ 2 NADH
Four ATP are produced by substrate-level phosphorylation.
2 ADP
2 ATP
2 pyruvate (C3) 14

14. Glycolysis glucose (C6) 2 ATP 2 ADP P-C6-P 2 C3-P 2 NAD+
2 ATP are consumed and 4 are produced. The net result is 2 ATP produced in glycolysis
2 NADH
2 P-C3-P
2 ADP
2 ATP
2 ADP
2 ATP
2 pyruvate (C3) 14

15. Summary of Glycolysis 4 ATP produced - 2 ATP consumed 2 ATP net
glucose (C6)
4 ATP produced
- 2 ATP consumed
2 ATP net
2 NADH are also produced
2 ATP
2 ADP
2C3
2 NAD+
2 ADP
2 ATP
2 NADH
2 ADP
2 ATP
2 pyruvate (C3) 15

16. glucose (C6)
Glycolysis
2 ATP
2 ADP
Summary - Glycolysis
2 C3
2 NAD+
2 ADP
2 NADH
2 ATP
2 ADP
2 ATP
2 pyruvate (C3)
This diagram summarizes glycolysis. As the discussion of cellular respiration proceeds, we will add to this diagram. 11

17. Formation of Acetyl CoA
Coenzyme A
2 pyruvate
(C3)
2 acetyl CoA
(C2)
(C3H3O3)
(C2H3O – S – CoA)
During this step, the pyruvate that was produced by glycolysis is converted to acetyl CoA by the removal of CO2. Pyruvate is a C3, acetyl CoA is a C2. 16

18. Formation of Acetyl CoA
Coenzyme A
2 pyruvate
(C3)
2 acetyl CoA
(C2)
2 NAD+
2 NADH
Two NAD+ molecules pick up two electrons each to become NADH. 17

19. Summary – Glycolysis, Acetyl CoA
glucose (C6)
Glycolysis
2 ATP
2 ADP
2 C3
Summary – Glycolysis, Acetyl CoA
2 NAD+
Formation of
Acetyl CoA
2 ADP
2 NADH
2 ATP
2 ADP
2 CO2
2 ATP
2 pyruvate (C3)
2 acetyl groups (C2)
2 NAD+
2 NADH
This diagram summarizes glycolysis and the formation of acetyl CoA. 11

20. Two Acetyl CoA Molecules
Each glucose molecule that initially began cellular respiration produce two acetyl CoA molecules (previous slide). The two acetyl CoA molecules will now enter the Krebs cycle.
The next several slides show the reactions that occur to one molecule of Acetyl CoA. Remember that the reactions must be repeated two times because there are two molecules of acetyl CoA for each glucose molecule that began cellular respiration.

21. Krebs Cycle C2 (acetyl CoA) Coenzyme A C6 C4 (C6H5O7)
The acetyl portion of acetyl CoA becomes bonded to a C4 molecule to produce a C6 molecule. C4
The above diagram is represented by the equation below:
Acetyl CoA + C4  C6 + Coenzyme A 18

22. Krebs Cycle C2 (acetyl CoA) C6 NADH C4 CO2 C5
A CO2 is removed from the C6 molecule to produce a C5 molecule. 19

23. Krebs Cycle C2 (acetyl CoA) C6 NADH C4 CO2 C5
CO2 has only one carbon (C1). The oxygen in CO2 came from the C6 molecule. 19

24. Krebs Cycle C2 (acetyl CoA) C6 NADH C4 CO2 C5
NADH is also produced from NAD+. 19

25. Krebs Cycle C2 (acetyl CoA) C6 NADH C4 CO2 C5 CO2 NADH ATP NADH FADH2
Another CO2 is then released.
NADH C4
CO2 C5
CO2
NADH
Two more NADH, one FADH2, and one ATP are produced.
ATP
NADH
FADH2 20

26. Krebs Cycle C2 (acetyl CoA) C6 NADH C4 CO2 C5 CO2 NADH ATP NADH FADH2
The ATP is produced by substrate-level phosphorylation. 20

27. Summary of the Krebs Cycle
Acetyl CoA enters the Krebs cycle.
The two carbon atoms are released in the form of CO2. C2 C6
NADH C4
CO2 C5
CO2
NADH
ATP
NADH
FADH2 20

28. Summary of the Krebs Cycle
C2 (acetyl CoA) C6
Three NADH, one FADH2 and one ATP are produced for each acetyl group.
NADH C4
CO2 C5
CO2
NADH
ATP
NADH
FADH2 20

29. Summary – Glycolysis, Acetyl CoA, Kreb’s Cycle
glucose (C6)
Glycolysis
2 ATP
2 ADP
Krebs Cycle
2 C3
2 NAD+
Formation of
Acetyl CoA
2 ADP
Summary – Glycolysis, Acetyl CoA, Kreb’s Cycle
2 NADH
2 ATP
2 C2 (acetyl CoA)
2 ADP
2 C6
2 CO2
2 NADH
2 ATP
2 pyruvate (C3)
2 acetyl groups (C2)
2 C4
2 CO2
2 C5
2 NAD+
2 NADH
2 NADH
2 CO2
2 ATP
2 FADH2
2 NADH 11

30. Electron Transport System
NADH and FADH2 produced during these reactions can be used to produce ATP.
The production of ATP using NADH and FADH2 involves the electron transport system, a system of proteins located on the inner membrane of the mitochondria.

31. Mitochondrion Structure
This drawing shows a mitochondrion cut lengthwise to reveal its internal components.
Intermembrane Space
Cristae Matrix

32. Mitochondrion - 1 outside inside intermembrane space
These red dots represent proteins in the electron transport system
inside
intermembrane
space 25

33. Mitochondrion - 2 H+ H+ H+ H+ H+ H+ NADH e- H+ H+ H+ H+ H+ H+ H+ H+
NADH and FADH2 from cellular respiration bring electrons to the electron transport system.
NADH e- H+ H+ H+ H+ H+ H+ H+ H+ 26

34. Mitochondrion - 3 H+ H+ H+ H+ H+ H+ e- H+ H+ H+ H+ H+ H+ H+ H+
When a carrier is reduced, some of the energy that is gained as a result of that reduction is used to pump hydrogen ions across the membrane into the intermembrane space. e- H+ H+ H+ H+ H+ H+ H+ H+ 27

35. Mitochondrion - 4 H+ H+ H+ H+ H+ e- H+ H+ H+ H+ H+ H+ H+ H+ H+
The electron is then passed to another carrier. e- H+ H+ H+ H+ H+ H+ H+ H+ H+ 28

36. Mitochondrion - 5 H+ H+ H+ H+ H+ e- H+ H+ H+ H+ H+ H+ H+ H+ H+
As before, some of the energy gained by the next carrier as a result of reduction is used to pump hydrogen ions into the intermembrane space. e- H+ H+ H+ H+ H+ H+ H+ H+ H+ 29

37. Mitochondrion -6 H+ H+ H+ H+ e- H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ 30

38. Mitochondrion -7 H+ H+ H+ H+ H+ e- H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ 31

39. Mitochondrion -8 H+ H+ H+ H+ e- H+ H+ H+ H+ H+ H+ H+ H+ H+ H+
Eventually, a concentration gradient of hydrogen ions is established in the intermembrane space (green on the diagram). e- H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ 32

40. Mitochondrion -9 H+ H+ H+ H+ H+ e- H+ H+ H+ H+ H+ H+ H+ H+
The last carrier must get rid of the electron. It passes it to oxygen to form water (next slide). e- H+ H+ H+ H+ H+ H+ H+ H+ H+ 34

41. Mitochondrion -10 H+ H+ H+ H+ 2H+ + 2e- + 1/2 O2  H2O H+ H+ H+ H+ H+
Note that e- + H+  H
Mitochondrion -10 H+ H+ H+ H+
Two electrons are required to form one molecule of water. The process therefore happens twice for each water molecule.
2H+ + 2e- + 1/2 O2  H2O H+ H+ H+ H+ H+ H+ H+ H+ H+ 34

42. Mitochondrion -11 H+ H+ H+ H+ H+ H+ H+ H+ ADP + Pi H+ H+ ATP H+ H+ H+
ATP synthase produces ATP by phosphorylating ADP. The energy comes from hydrogen ions forcing their way into the matrix as they pass through the ATP synthase (due to osmotic pressure).
ADP + Pi H+ H+ H+
ATP H+ H+ H+ H+ 33

43. Summary of Oxidative Phosphorylation
2H+ + 2e- + 1/2 O2  H2O
NADH H+ H+ H+ H+
ADP + Pi H+ H+ H+
ATP H+ H+ H+ H+ 33

44. Summary – Glycolysis, Acetyl CoA, Kreb’s Cycle, Electron Transport
glucose (C6)
Glycolysis
2 ATP
2 ADP
Krebs Cycle
2 C3
Summary – Glycolysis, Acetyl CoA, Kreb’s Cycle, Electron Transport
2 NAD+
Formation of
Acetyl CoA
2 ADP
2 NADH
2 ATP
2 C2 (acetyl CoA)
2 ADP
2 C6
2 CO2
2 NADH
2 ATP
2 pyruvate (C3)
2 acetyl groups (C2)
2 C4
2 CO2
2 C5
2 NAD+
2 NADH
2 NADH
2 CO2
2 ATP
2 FADH2
2 NADH
10 NAD+
2 FAD
electron
transport
1/2 O2
32 ATP
H2O 11

45. Summary of Cellular Respiration
glucose
Glycolysis
2 pyruvate
2 ATP
2 NADH

46. Summary CO2 C C C glucose Glycolysis 2 pyruvate 2 ATP 2 NADH
Acetyl CoA
2 acetyl CoA
2CO2
2NADH

47. Summary CO2 C CO2 C C glucose Glycolysis 2 pyruvate 2 ATP 2 NADH
Acetyl CoA
2 acetyl CoA
2CO2
2NADH
Krebs Cycle
4 CO2
2 ATP
6 NADH
2 FADH2

48. ATP Yield per Glucose Pathway Substrate-Level Phosphorylation
Oxidative Phosphorylation
Total ATP
Glycolysis 2
2 NADH (= 4 ATP) 6
Glycolysis occurs in the cytoplasm of the cell. NADH produced in the cytoplasm must be brought into the mitochondrion before ATP is produced. Each NADH produced in glycolysis results in 2 ATP.

49. These NADH result in the production of 2 ATP each because they are produced outside the mitochondrion and must be transported in.
ATP Yield per Glucose
Pathway
Substrate-Level Phosphorylation
Oxidative Phosphorylation
Total ATP
Glycolysis 2
2 NADH (= 4 ATP) 6
Formation of Acetyl CoA
2 NADH (= 6 ATP)
Acetyl CoA is formed in the mitochondrion. Because the NADH produced is already in the mitochondrion, each NADH results in the production of 3 ATP.

50. ATP Yield per Glucose Pathway Substrate-Level Phosphorylation
Oxidative Phosphorylation
Total ATP
Glycolysis 2
2 NADH (= 4 ATP) 6
Formation of Acetyl CoA
2 NADH (= 6 ATP)
Krebs Cycle
6 NADH (= 18 ATP)
2 FADH2 (= 4 ATP) 24

51. ATP Yield per Glucose Pathway Substrate-Level Phosphorylation
Oxidative Phosphorylation
Total ATP
Glycolysis 2
2 NADH (= 4 ATP) 6
Formation of Acetyl CoA
2 NADH (= 6 ATP)
Krebs Cycle
6 NADH (= 18 ATP)
2 FADH2 (= 4 ATP) 24
Total 4 32 36

52. Glycolysis Krebs Cycle Formation of Acetyl CoA electron transport
Fermentation does not involve the formation of acetyl CoA, the Krebs Cycle, or oxidative phosphorylation.
glucose (C6)
Glycolysis
2 ATP
2 ADP
Krebs Cycle
2 C3
Fermentation
2 NAD+
Formation of
Acetyl CoA
2 ADP
2 NADH
2 ATP
2 C2 (acetyl CoA)
2 ADP
2 C6
2 CO2
2 NADH
2 ATP
2 pyruvate (C3)
2 acetyl groups (C2)
2 C4
2 CO2
2 C5
2 NAD+
2 NADH
2 NADH
2 CO2
2 ATP
2 FADH2
2 NADH
10 NAD+
2 FAD
electron
transport
1/2 O2
32 ATP
H2O 11

53. Fermentation includes glycolysis plus several additional steps.
glucose (C6)
Glycolysis
2 ATP
2 ADP
2 C3
Fermentation
2 NAD+
2 ADP
2 NADH
2 ATP
2 ADP
2 ATP
2 pyruvate (C3) 11

54. Fermentation 2 ADP 2 NAD+ 2 ATP 2 NADH
Glycolysis requires a supply of NAD+.
2 ADP
2 ATP
2 NAD+
2 NADH
NADH must reduce (donate its electrons) to another molecule in order to regenerate NAD+.
Otherwise, all of the NAD+ will be used up as it is converted to NADH and glycolysis will stop. 42

55. Fermentation glucose 2 ADP 2 NAD+ 2 ATP pyruvate 2 NADH lactate or
alcohol
2 ADP
2 ATP
2 NAD+
2 NADH
NADH gives its electron to pyruvate, which is reduced to form either lactate or alcohol.
(animals, bacteria)
(plants, fungi) 43

56. Substrate-Level Phosphorylation
Phosphate groups
High-energy molecule
ADP
Enzyme

57. Substrate-Level Phosphorylation

58. Substrate-Level Phosphorylation
Low-energy molecule
ATP

59. NAD+ (Nicotinamide Adenine Dinucleotide)
Organic Molecule
Organic Molecule
NAD+ + + +
NAD+ + 2H  NADH + H+
NAD+ functions in cellular respiration by carrying two electrons. With two electrons, it becomes NADH.
NAD+ oxidizes its substrate by removing two hydrogen atoms. One of the hydrogen atoms bonds to the NAD+. The electron from the other hydrogen atom remains with the NADH molecule but the proton (H+) is released. 
NAD+ + 2H ® NADH + H+
NADH then donate the two electrons (one of them is a hydrogen atom) to another molecule.

60. Review: NAD+ + 2H  NADH + H+
Energy + 2H
Energy + 2H
NAD+
NAD+ is an electron carrier. 53

61. Review: A Cyclic Metabolic Pathway
A + F  B
B  C  D
D  F + E F C D E 7