1. Chapter 07 Cellular Respiration
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2. 7.1 Overview of Cellular Respiration-1
Cellular respiration is the release of energy from molecules such as glucose accompanied by the use of this energy to synthesize ATP molecules.
Aerobic – requires O2
Gives off CO2
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3. 7.1 Overview of Cellular Respiration-2
Glucose is a high-energy molecule, and as it is broken down, energy is released.
This energy is used to produce ATP.
The breakdown of one glucose molecule results in 36 or 38 ATP molecules.
The pathways of cellular respiration allow the energy within a glucose molecule to be released slowly for ATP synthesis.

4. NAD+ and FAD-1
Cellular respiration involves many individual reactions, each requiring its own enzyme.
Certain enzymes utilize two coenzymes.
NAD+ (nicotinamide adenine dinucleotide)
FAD (flavin adenine dinucleotide)
Each carries two electrons and two hydrogen atoms.
They pick up electrons at specific enzymatic reactions and carry these electrons to the electron transport chain.

5. NAD+ and FAD-2 Figure 7.1 Jump to long image description
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6. Phases of Cellular Respiration-1
Glycolysis
Preparatory Reaction
Citric Acid Cycle
Electron Transport Chain

7. Phases of Cellular Respiration-2
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Figure 7.2
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8. Phases of Cellular Respiration-3
Glycolysis is the breakdown of glucose into two molecules of pyruvate.
Oxidation by removal of electrons (e-) and hydrogen ions (H+) provides the energy for the immediate buildup of two ATP.

9. Phases of Cellular Respiration-4
Preparatory (Prep) Reaction
Pyruvate is oxidized to acetyl CoA and carbon dioxide is removed.
One three-carbon molecule becomes one two-carbon molecule.
Prep reaction occurs twice because glycolysis produces two pyruvates.

10. Phases of Cellular Respiration-5
Citric Acid Cycle
Cyclical series of oxidation reactions that produce one ATP and carbon dioxide per turn
Acetyl CoA is converted to citric acid and enters the cycle
Citric acid cycle turns twice because two acetyl CoAs are produced per glucose

11. Phases of Cellular Respiration-6
Electron Transport Chain
Series of electron carrier molecules
Electrons are passed from one carrier to another.
As the electrons move from a higher energy state to a lower one, energy is released to make ATP.
Under aerobic conditions, ATP per glucose molecule can be produced.

12. Phases of Cellular Respiration-7
Figure 7.3
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13. Phases of Cellular Respiration-8
Pyruvate is a pivotal metabolite in cellular respiration
If no oxygen is available, pyruvate is reduced to lactate (in animals) or alcohol and carbon dioxide (in plants) in a process called fermentation.
Fermentation results in a net gain of two ATP/glucose.

14. 7.2 Outside the Mitochondria: Glycolysis-1
Glycolysis is the breakdown of glucose to two molecules of pyruvate.
Takes place in the cytoplasm
Does not require oxygen
Transforms one 6-carbon molecule into two 3-carbon molecules

15. 7.2 Outside the Mitochondria: Glycolysis-2
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16. 7.2 Outside the Mitochondria: Glycolysis-3
Energy Investment Steps
Two molecules of ATP used to activate glucose as glycolysis begins
Energy Harvesting Steps
Oxidation of G3P results in NADH synthesis
Additional chemical changes lead to direct substrate-level phosphorylation, formation of 4 ATP

17. Substrate-level ATP Synthesis
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18. Inputs and Outputs of Glycolysis
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19. Glycolysis: Energy-investment Step-1
Figure 7.4(a)
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20. Glycolysis: Energy-harvesting Steps-2
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Figure 7.4(b)
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21. 7.3 Outside the Mitochondria: Fermentation
If O2 is limited, cells may utilize anaerobic pathways, such as fermentation.
Two basic forms of fermentation:
Lactic acid
Alcohol

22. Lactic Acid Fermentation-1
In animal cells, pyruvate from glycolysis accepts two hydrogen ions and two electrons and is reduced to lactate.
Two NADH pass electrons to pyruvate to reduce it to lactate.

23. Lactic Acid Fermentation-2
Fermentation is essential to humans since it can provide a rapid burst of ATP.
In muscles working vigorously over a short period, fermentation is used to produce ATP as O2 is in limited supply.
Lactate is toxic to cells.
As it accumulates, lactate changes the pH of the muscle cells, causing the “burn” feeling.

24. Alcohol Fermentation Yeast generates ethyl alcohol by fermentation.
As with lactic acid fermentation, electrons needed to reduce the pyruvate are supplied by NADH molecules.
Unlike lactic acid fermentation, alcohol fermentation releases small amounts of carbon dioxide.

25. Energy Yield of Fermentation-1
Fermentation yields only two ATP by substrate-level ATP synthesis.
These two ATP represent a small fraction of potential energy stored in glucose.
In cellular respiration, 36 to 38 ATP molecules are produced.
Therefore, most of the potential energy stored in glucose has not been released.

26. Energy Yield of Fermentation-2
Figure 7.5
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27. Energy Yield of Fermentation-3
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28. 7.4 Inside the Mitochondria
Preparatory Reaction
Produces the molecule that will enter the citric acid cycle.
Reaction occurs in the cristae of mitochondria
Cristae are folds of the inner membrane that jut out into the matrix
3C pyruvate is converted to 2C acetyl group

29. Preparatory Reaction Acetyl group attaches to CoA to become acteyl CoA
Carbon dioxide is produced
Hydrogen atoms are removed from pyruvate and picked up to form NADH + H+
This reaction occurs twice per glucose.
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30. Citric Acid Cycle-1 Citric Acid Cycle
Cyclical pathway that occurs in the matrix of mitochondria
A two-carbon acetyl group of Acetyl CoA combines with a C4 molecule (oxaloacetate) to produce C6 citrate.
The CoA is recycled to the preparatory reaction.

31. Citric Acid Cycle-2
Each two-carbon acetyl group is oxidized to two CO2 molecules.
Reactions produce three NADH + H+ and one FADH2 .
One ATP is produced by substrate-level ATP synthesis.
Cycle turns twice per original glucose molecule.

32. Citric Acid Cycle-3 Page 119
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33. Citric Acid Cycle-4 Figure 7.6(a)
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34. Citric Acid Cycle-5 Figure 7.6(b)
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35. Electron Transport Chain-1
Located in cristae of mitochondria
Electrons are passed to a series of electron carriers.
Some carriers are cytochromes, iron-containing proteins.
High-energy electrons enter the system and low-energy electrons leave the system.
Two electrons per NADH + H+ and FADH2 enter the electron transport chain.
Each carrier is reduced and then oxidized.

36. Electron Transport Chain-2
As electrons pass from one carrier to another, energy is captured and stored as a hydrogen ion concentration gradient.
Oxygen combines with hydrogen ions to form water.
NAD+ and FAD are recycled to pick up more electrons from glycolysis, prep reaction, and citric acid cycle.

37. Electron Transport Chain-3
Figure 7.7(a)
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38. Electron Transport Chain-4
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Figure 7.7(b)

39. Generating ATP-1
Electron carriers are located in the cristae of the mitochondria.
NADH pass electrons to the first acceptor of the electron transport chain.
As electrons pass along a series of electron carriers, the energy released is used to pump H+ into the intermembrane space of mitochondrion.
Protons accumulate in the intermembrane space (proton gradient).

40. Generating ATP-2 The cristae also have ATP synthase complexes.
The H+ ions flow through an ATP synthase complex, back into the matrix.
As the H+ pass through the complex, energy is released and captured to form ATP from ADP.
This process is called chemiosmosis.

41. Generating ATP-3 Figure 7.8(a)
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42. Generating ATP-4 Figure 7.8(b)
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Figure 7.8(b)

43. Energy Yield from Cellular Respiration-1
What is the energy yield for the complete breakdown of glucose to CO2 and H2O?
Total of 4 ATP by substrate-level ATP synthesis
2 net from glycolysis
2 from citric acid cycle
32-34 ATP produced by electron transport chain and chemiosmosis
Some cells have to pay to pump NADH from glycolysis into mitochondria

44. Energy Yield from Cellular Respiration-2
Figure 7.9
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45. Efficiency of Cellular Respiration-3
The difference in energy content of reactants (glucose and oxygen) and products (carbon dioxide and water) is 686 kcal.
ATP phosphate bond has 7.3 kcal of energy.
36 ATP are produced in respiration.
36 X 7.3 = 263 kcal
263/686 = 39% efficiency of energy capture
The rest of the energy is lost as heat.