1. Cellular Respiration: Harvesting Chemical Energy Figures 6.6 – 6.16
CHAPTER 6
Cellular Respiration: Harvesting Chemical Energy
Figures 6.6 – 6.16

2. NADH and Electron Transport Chains
The path that electrons take on their way down from glucose to oxygen involves many stops
1/2
(from food via NADH)
Energy for
synthesis of
2 H
2 e
Electron transport chain
2 e
1/2
2 H
Figure 6.6

3. The first stop is an electron acceptor called NAD+
The transfer of electrons from organic fuel to NAD+ reduces it to NADH
The rest of the path consists of an electron transport chain
This chain involves a series of redox reactions
These lead ultimately to the production of large amounts of ATP

4. The Metabolic Pathway of Cellular Respiration
Cellular respiration is an example of a metabolic pathway
A series of chemical reactions in cells
All of the reactions involved in cellular respiration can be grouped into three main stages
Glycolysis
The Krebs cycle
Electron transport

5. A Road Map for Cellular Respiration
Cytosol
Mitochondrion
High-energy
electrons
carried
by NADH
High-energy
electrons carried
mainly by
NADH
Glycolysis 2
Pyruvic
acid
Krebs
Cycle
Electron
Transport
Glucose
Figure 6.7

6. Stage 1: Glycolysis
A molecule of glucose is split into two molecules of pyruvic acid

7. Glycolysis breaks a six-carbon glucose into two three-carbon molecules
These molecules then donate high energy electrons to NAD+, forming NADH

8. 2 Pyruvic acid
Glucose
Figure 6.8

9. Glycolysis makes some ATP directly when enzymes transfer phosphate groups from fuel molecules to ADP
Figure 6.9

10. Stage 2: The Krebs Cycle
The Krebs cycle completes the breakdown of sugar

11. In the Krebs cycle, pyruvic acid from glycolysis is first “prepped” into a usable form, Acetyl-CoA2 1
Acetic
acid 3
Pyruvic
acid
Acetyl-CoA
(acetyl-coenzyme A)
CO2
Coenzyme A
Figure 6.10

12. The Krebs cycle extracts the energy of sugar by breaking the acetic acid molecules all the way down to CO2
The cycle uses some of this energy to make ATP
The cycle also forms NADH and FADH2

13. Krebs Cycle Input Output Acetic acid 2 CO2 ADP 3 NAD FAD 2 1 3 4 5 6
Figure 6.11

14. Stage 3: Electron Transport
Electron transport releases the energy your cells need to make the most of their ATP

15. The molecules of electron transport chains are built into the inner membranes of mitochondria
The chain functions as a chemical machine that uses energy released by the “fall” of electrons to pump hydrogen ions across the inner mitochondrial membrane
These ions store potential energy

16. When the hydrogen ions flow back through the membrane, they release energy
The ions flow through ATP synthase
ATP synthase takes the energy from this flow and synthesizes ATP

17. Electron transport chain
Protein
complex
Electron
carrier
Inner
mitochondrial
membrane
Electron
flow
Electron transport chain
ATP synthase
Figure 6.12

18. The Versatility of Cellular Respiration
Cellular respiration can “burn” other kinds of molecules besides glucose
Diverse types of carbohydrates
Fats
Proteins

19. Food Polysaccharides Fats Proteins Sugars Glycerol Fatty acids
Amino acids
Amino groups
Acetyl-
CoA
Krebs
Cycle
Glycolysis
Electron
Transport
Figure 6.13

20. Adding Up the ATP from Cellular Respiration
Cytosol
Mitochondrion
Glycolysis 2
Acetyl-
CoA 2
Pyruvic
acid
Krebs
Cycle
Electron
Transport
Glucose
Maximum
per
glucose: by
direct
synthesis by
ATP
synthase
by direct
synthesis
Figure 6.14

21. FERMENTATION: ANAEROBIC HARVEST OF FOOD ENERGY
Some of your cells can actually work for short periods without oxygen
For example, muscle cells can produce ATP under anaerobic conditions
Fermentation
The anaerobic harvest of food energy

22. Fermentation in Human Muscle Cells
Human muscle cells can make ATP with and without oxygen
They have enough ATP to support activities such as quick sprinting for about 5 seconds
A secondary supply of energy (creatine phosphate) can keep muscle cells going for another 10 seconds
To keep running, your muscles must generate ATP by the anaerobic process of fermentation

23. Glycolysis is the metabolic pathway that provides ATP during fermentation
Pyruvic acid is reduced by NADH, producing NAD+, which keeps glycolysis going
In human muscle cells, lactic acid is a by-product

24. (a) Lactic acid fermentation
2 ADP+ 2
Glycolysis
2 NAD
2 NAD
Glucose
2 Pyruvic
acid
+ 2 H
2 Lactic
acid
(a) Lactic acid fermentation
Figure 6.15a

25. Fermentation in Microorganisms
Various types of microorganisms perform fermentation
Yeast cells carry out a slightly different type of fermentation pathway
This pathway produces CO2 and ethyl alcohol

26. (b) Alcoholic fermentation
2 ADP+ 2
2 CO2 released
2 ATP
Glycolysis
2 NAD
2 NAD
Glucose
2 Ethyl
alcohol
2 Pyruvic
acid
+ 2 H
(b) Alcoholic fermentation
Figure 6.15b

27. The food industry uses yeast to produce various food products
Figure 6.16

28. EVOLUTION CONNECTION: LIFE ON AN ANAEROBIC EARTH
Ancient bacteria probably used glycolysis to make ATP long before oxygen was present in Earth’s atmosphere
Glycolysis is a metabolic heirloom from the earliest cells that continues to function today in the harvest of food energy

29. SUMMARY OF KEY CONCEPTS
Chemical Cycling Between Photosynthesis and Cellular Respiration
Heat
Sunlight
Cellular
respiration
Photosynthesis
Visual Summary 6.1

30. The Overall Equation for Cellular Respiration
Oxidation:
Glucose loses electrons
(and hydrogens)
Glucose
Carbon dioxide
Electrons
(and hydrogens)
Energy
Reduction:
Oxygen gains
electrons (and
hydrogens)
Oxygen
Visual Summary 6.2

31. The Metabolic Pathway of Cellular Respiration
Glucose
Oxygen
Water
Energy
Visual Summary 6.3