1. The process by which cells harvest the energy stored in food
Cellular respiration
The process by which cells harvest the energy stored in food

2. SAVING FOR A Rainy Day

3. Feel the Burn

4. How do living organisms fuel their actions
How do living organisms fuel their actions? Cellular respiration: the big picture

5. ATP
Adenine
Ribose
3 Phosphate groups

6. ATP ATP Adenosine diphosphate (ADP) + Phosphate
Energy
Adenosine diphosphate (ADP) + Phosphate
Adenosine triphosphate (ATP)
Partially
charged
battery
Fully

7. Fermentation (without oxygen)
Chemical Pathways
Section 9-1
Glucose
Glycolysis
Krebs cycle
Electron transport
Fermentation (without oxygen)
Alcohol or lactic acid

8. Cellular Respiration: The Big Picture
Energy (ATP)
C6H12O6 + 6O2 →↑→ 6CO2 + 6H2O
Glucose + 6 Oxygen →↑→ 6 Carbon dioxide Water

9. Cellular Respiration: The big picture
All living organisms extract energy from the chemical bonds of molecules (which can be considered “food”) through a process called cellular respiration.
To generate energy, fuels such as glucose and other carbohydrates, proteins, and fats are broken down in three steps: (1) glycolysis, (2) the Krebs cycle, and (3) the electron transport chain.
Figure 4-34 The steps of cellular respiration: from glucose to usable energy. 9

10. Cellular Respiration: The Big Picture
Section 9-1
Mitochondrion
Electrons carried in NADH
Electrons carried in NADH and FADH2
Pyruvic acid
Glucose
Electron Transport Chain
Krebs Cycle
Glycolysis
Mitochondrion
Cytoplasm

11. Four-Step Process
Glycolysis (terribly inefficient) occurs in the cytoplasm; the Krebs cycle and the electron transport chain occur in the mitochondria. Acetyl-CoA production is a necessary preparatory step to the Krebs cycle.
Figure 4-34 The steps of cellular respiration: from glucose to usable energy. 11

12. Electron Transport Chain
Cellular Respiration
Section 9-2
Glucose (C6H1206) +
Oxygen (02) 1
Glycolysis 2
Acetyl
CoA 3
Krebs Cycle 4
Electron Transport Chain
Carbon
Dioxide
(CO2) +
Water
(H2O)

13. Cellular Respiration
Requires (1) fuel and (2) oxygen.

14. Cellular Respiration

15. In Humans…
our cells can extract some of the energy stored in the bonds of the food molecules
Energy
Bonds
Molecules

16. Aerobic Respiration – the video

17. Glycolysis is the universal energy-releasing pathway
splitting (lysis) of sugar (glyco)
All organisms
single-celled organisms

18. Glycolysis is the universal energy-releasing pathway

19. Glycolysis Three of the ten steps yield energy
High-energy electrons are transferred to NADH
Net result:
pyruvate
ATP molecules
NADH molecules

20. Glycolysis
Glucose (6C) is broken down into 2 PGAL (Phosphoglyceraldehyde – 3 Carbon molecules)
Cost: 2 ATP

21. Glycolysis 2 PGAL (3C) are converted to 2 pyruvates
Result: 4 ATP, 2 NADH
net ATP production = 2 ATP

23. How Glycolysis Works
Animation

24. Glycolysis: The Movie

25. Glycolysis is very inefficient
Pyruvate can be further metabolized to yield more energy
Answer: 4 25

26. The mitochondrion

27. The “bag-within-a-bag”
Material inside the mitochondrion can lie in one of two spaces: (1) the intermembrane space, which is outside of the inner bag, or (2) the mitochondrial matrix, which is inside the inner bag.
With two distinct regions separated by a membrane, the mitochondrion can create higher concentrations of molecules in one area or the other. And because a concentration gradient is a form of potential energy—molecules move from the high concentration area to the low concentration area the way water rushes down a hill—once a gradient is created, the energy released as the gradient equalizes itself can be used to do work. In the electron transport chain, this energy is used to build the energy-rich molecule ATP.
Figure 4-32 “A bag within a bag.” 27

28. The Preparatory Phase to the Krebs Cycle
The two pyruvate molecules move into the mitochondria and then undergo three quick modifications that prepare them to be broken down in the Krebs cycle:
Modification 1. Each pyruvate molecule passes some of its high-energy electrons to the energy-accepting molecule NAD+, building two molecules of NADH.
Modification 2. Next, a carbon atom and two oxygen atoms are removed from each pyruvate molecule and released as carbon dioxide. The CO2 molecules diffuse out of the cell and, eventually, out of the organism. In humans, for example, these CO2 molecules pass into the bloodstream and are transported to the lungs, from which they are eventually exhaled.
Modification 3. In the final step in the preparation for the Krebs cycle, a giant compound known as coenzyme A attaches itself to the remains of each pyruvate molecule, producing two molecules called acetyl-CoA. Each acetyl-CoA molecule is now ready to enter the Krebs cycle.
Figure 4-30 Preparations of pyruvate. 28

29. The Conversion of Pyruvate to Acetyl Co-A for Entry Into the Krebs Cycle
glycolysis (cytoplasm), pyruvic acid  interior of mitochondrion

30. The Conversion of Pyruvate to Acetyl Co-A for Entry Into the Kreb's Cycle
2 NADH are generated
2 CO2 are released

31. The Krebs Cycle extracts energy from sugar

32. There are eight separate steps in the Krebs cycle
There are eight separate steps in the Krebs cycle. Three general outcomes are depicted here.
Outcome 1. A new molecule is formed. Acetyl-CoA adds its two-carbon acetyl group to a molecule of the starting material of the Krebs cycle, a four-carbon molecule called oxaloacetate. This process creates a six-carbon molecule.
Outcome 2. High-energy electron carriers (NADH) are made and carbon dioxide is exhaled. The six-carbon molecule then gives electrons to NAD+ to make the high-energy electron carrier NADH. The six-carbon molecule releases two carbon atoms along with four oxygen atoms to form two carbon dioxide molecules. This CO2 is carried by the bloodstream to the lungs from which it is exhaled into the atmosphere.
Outcome 3. The starting material of the Krebs cycle is re-formed, ATP is generated, and more high-energy electron carriers are formed. After the CO2 is released, the four-carbon molecule that remains from the original pyruvate-oxaloacetate molecule formed in Outcome 1 is modified and rearranged to once again form oxaloacetate, the starting material of the Krebs cycle. In the process of this reorganization, one ATP molecule is generated and more electrons are passed to one familiar high-energy electron carrier, NADH, and a new one, FADH2. The formation of these high-energy electron carriers increases the energy yield of the Krebs cycle. One oxaloacetate is reformed, the cycle is ready to break down the second molecule of acetyl-CoA. Two turns of the cycle are necessary to completely dismantle our original molecule of glucose.
Figure Overview of the Krebs cycle. 32

33. The Kreb’s Cycle extracts energy from sugar
6 NADH
2 FADH2
2 ATP
4 CO2 (to atmosphere)

34. The Krebs Cycle extracts energy from sugar

35. The Kreb’s Cycle extracts energy from sugar
Animation

36. Krebs: The Movie

37. Krebs: The Movie (Part 2)

38. the electron transport chain
2 key features of mitochondria

39. the electron transport chain
2 mitochondrial spaces  higher concentrations of molecules in one area or the other

40. The “bag-within-a-bag”
Material inside the mitochondrion can lie in one of two spaces: (1) the intermembrane space, which is outside of the inner bag, or (2) the mitochondrial matrix, which is inside the inner bag.
With two distinct regions separated by a membrane, the mitochondrion can create higher concentrations of molecules in one area or the other. And because a concentration gradient is a form of potential energy—molecules move from the high concentration area to the low concentration area the way water rushes down a hill—once a gradient is created, the energy released as the gradient equalizes itself can be used to do work. In the electron transport chain, this energy is used to build the energy-rich molecule ATP.
Figure 4-32 “A bag within a bag.” 40

41. Follow the Electrons, as We Did in Photosynthesis
Start with the electrons carried by NADH and FADH2.
Over-the-counter NADH pills provide energy to sufferers of chronic fatigue syndrome. Why might this be?
Figure 4-33 The big energy payoff
#2) This proton concentration gradient represents a significant source of potential energy! 41

42. Proton Gradients and Potential Energy

43. Electron Transport: The Movie

44. Electron Transport: The Movie (Part 2)

45. Figure 4-34 The steps of cellular respiration: from glucose to usable energy.

46. Review of Cellular Respiration
Review Animation

47. Energy is obtained from a molecule of glucose in a stepwise fashion.
Answer: 2 47

48. Plants have both chloroplasts and mitochondria.
Answer: 3 48

49. The Fate of Pyruvate
Yeast: pyruvic acid is decarboxylated and reduced by NADH to form a molecule of carbon dioxide and one of ethanol
accounts for the bubbles and alcohol in, for examples, beer and champagne (alcoholic fermentation)
process is energetically wasteful because so much of the free energy of glucose (~95%) remains in the alcohol (a good fuel!)
Red blood cells and active muscles: pyruvic acid is reduced by NADH forming a molecule of lactic acid (lactic acid fermentation)
process is energetically wasteful because so much free energy remains in the lactic acid molecule
Mitochondria: pyruvic acid is oxidized completely to form CO2 & H2O (cellular respiration)
~ 40% of energy in original glucose molecule is trapped in molecules of ATP

50. Alternative Pathways to Energy
Rapid, strenuous exertion
 O2 deficiency

51. Alternative Pathways to Energy
NAD+ /FAD+ halted
back-up method for breaking down sugar
lactic acid

52. Alternative Pathways to Energy Acquisition
Animation: Lactic Acid Fermentation

53. Alternative Pathways to Energy Acquisition
Yeast
acetaldehyde
produce alcohol only in the absence of oxygen

54. Alternative Pathways to Energy Acquisition
Animation: Alcoholic Fermentation

55. With rapid, strenuous exertion, our bodies soon fall behind in delivering oxygen from the lungs to the bloodstream to the cells and finally to the mitochondria.
Oxygen deficiency then limits the rate at which the mitochondria can break down fuel and produce ATP.
This slowdown in ATP production occurs because the electron transport chain requires oxygen as the final acceptor of all the electrons that are generated during glycolysis and the Krebs cycle.
If oxygen is in short supply, the electrons from NADH (and FADH2) have nowhere to go.
Consequently, the regeneration of NAD+ (and FAD+) in the electron transport chain is halted, leaving no recipient for the high-energy electrons harvested from the breakdown of glucose and pyruvate, and the whole process of cellular respiration can grind to a stop.
Organisms don’t let this interruption last long, though; most have a back-up method for breaking down sugar.
Among animals, there is one willing acceptor for the NADH electrons in the absence of oxygen: pyruvate, the end product of glycolysis.
When pyruvate accepts the electrons, it forms lactic acid.
Figure 4-36 Energy production compared: with and without oxygen. 55

56. anaerobic respiration
Answer: 5 56

57. Cells can run on protein and fat as well as on glucose
4-17. Eating a complete diet: cells can run on protein and fat as well as on glucose.
Evolution has built humans and other organisms with the metabolic machinery that allows them to extract energy and other valuable chemicals from proteins, fats, and a variety of carbohydrates.
For that reason, we are able to consume and efficiently utilize meals comprising various combinations of molecules:
Sugars: In the case of dietary sugars, many are polysaccharides—multiple simple sugars linked together—rather than solely the simple sugar glucose. Before they can be broken down by cellular respiration, the polysaccharides must first be separated by enzymes into glucose or related simple sugars that can be broken down by cellular respiration.
Lipids: Dietary lipids are broken down into their two constituent parts: a glycerol molecule and a fatty acid. The glycerol is chemically modified into one of the molecules produced during one of the ten steps of glycolysis. It then enters glycolysis at that step in the process and is broken down to yield energy. The fatty acids, meanwhile, are chemically modified into acetyl-CoA, at which point they enter the Krebs cycle.
Proteins: Proteins are chains of amino acids. Upon consumption they are broken down chemically into their constituent amino acids. Once that is done, each amino acid is broken down into (1) an amino group that may be used in the production of tissue or excreted in the urine and (2) a carbon compound that is converted into one of the intermediate compounds in glycolysis or the Krebs cycle, allowing the energy stored in its chemical bonds to be harnessed. 57