1. Cellular Respiration: Harvesting Chemical Energy
Chapter 9 notes
Cellular Respiration: Harvesting Chemical Energy

2. Concept 9.1
Metabolic pathways that release energy are called catabolic pathways
- fermentation and cellular respiration
Fermentation: partial degradation of sugars that occurs w/out the help of O2
Cellular respiration: O2 is consumed as a reactant along w/ the sugar
- more efficient

3. Concept 9.1 Cellular respiration occurs in the mitochondria
Organic + O2  Carbon + H2O + Energy
compounds dioxide
C6H12O6 + 6O2  6CO2 + 6H2O + Energy
1 glucose = -686 kcals

4. Concept 9.1
ATP is the central molecule responsible for energy used by the cell
The cell uses enzymes to transfer phosphate groups from ATP to other compounds (making them phosphorylated)
ATP  ADP + phosphate

5. Concept 9.1
Redox reactions release energy when electrons move closer to electronegative atoms
- the relocation of electrons releases the energy stored in food molecules, and this energy is used to synthesize ATP

6. Concept 9.1
There is a transfer of one or more e- from one reactant to another; the electron transfers are called oxidation-reduction reactions or redox rxns.
- the loss of e- from one substance is called oxidation
- the addition of e- to another substance is called reduction

7. Concept 9.1

8. Concept 9.1
Electrons “fall” from organic molecules to oxygen during cellular respiration
C6H12O6 + 6O2  6CO2 + 6H2O + Energy
- by oxidizing glucose, cellular respiration takes energy out of storage and makes it available for ATP synthesis
- carbohydrates and fats are reservoirs of electrons associated w/ hydrogen

9. Concept 9.1
The “fall” of electrons during respiration is stepwise, via NAD+ and an electron transport chain
Glucose is broken down over a series of steps that are each catalyzed by a specific enzyme
Hydrogen atoms are stripped from the glucose and usually passed to NAD+.
- NAD+ is reduced in the rxn.

10. Concept 9.1 NAD+ is transformed to NADH
- NADH will later be tapped to make ATP as the electrons continue their fall from NADH to oxygen
Respiration uses an electron transport chain to break the fall of electrons to oxygen into several energy-releasing steps instead of one explosive rxn.

11. Concept 9.1

12. Concept 9.1
Electrons removed from food are shuttled by NADH to the “top” end of the chain. At the “bottom”, oxygen captures the electrons along with H+ ions to form water
Food NADH  ETC  oxygen

13. Concept 9.1 Respiration consists of three stages:
- glycolysis, the Krebs cycle, electron transport chain (ETC)
Glycolysis breaks down 1 glucose into 2 molecules of pyruvate
- occurs in the cytosol
Krebs cycle breaks down pyruvate into CO2
- occurs in the mitochondrial matrix

14. Concept 9.1
ETC accepts electrons from the breakdown products of the first 2 stages
- the energy released at each step of the chain is used to make ATP (oxidative phosphorylation); through redox rxns.
oxidative phosphorylation accounts for 90% of generated ATP

15. Concept 9.1

16. Concept 9.1

17. Concept 9.1

18. Concept 9.1
Substrate-level phosphorylation: direct transfer of a phosphate to ADP by an enzyme
Each molecule of glucose is degraded into carbon dioxide, water and 38 molecules of ATP

19. Concept 9.1

20. Concept 9.2 Glycolysis means “splitting of sugar”
- the 10 steps of glycolysis are broken down into two phases: energy investment and energy payoff
- glucose (6C) 2 pyruvate (3C)
Energy investment phase: the cell spends 2 ATP to phosphorylate the fuel molecules

21. Concept 9.2
Energy payoff phase: 4 ATP are produced by substrate-level phosphorylation; 2 NAD+ are reduced to 2 NADH by the oxidation of food
Net energy yield: 2 ATP and 2 NADH

23. Concept 9.3
If O2 is present, energy stored in NADH can be converted to ATP
Upon entering the mitochondrion, each pyruvate is first converted to a molecule of acetyl CoA (2C)
- another NAD+ is reduced to NADH

24. Concept 9.3

25. Concept 9.3
Acetyl CoA will enter the Krebs cycle for further oxidation
Krebs cycle
- 8 steps, each catalyzed by a specific enzyme
- Acetyl CoA (2C) enters, 2 CO2 (1C) leave, 3 NAD+  3 NADH, 1 FAD  1 FADH2, 1 ADP  1 ATP

26. Concept 9.3

27. Concept 9.4 Cristae: inner membrane folding of the mitochondria
- increases surface area for more ETC’s
Electrons removed from food during gycolysis/Krebs are transferred by NADH to the first molecule of the ETC

28. Concept 9.4

29. Concept 9.4
Most of the electron carriers in the ETC are proteins called cytochromes (cyt).
The process goes downhill with oxygen being the final e- acceptor
- for every 2 NADH, 1 O2 molecule is reduced into 2 molecules of water

30. Concept 9.4
FADH2 adds its e- at a lower energy level than NADH on the ETC.
-NADH = 3 ATP
- FADH2 = 2 ATP
ETC makes no ATP directly. It moves e- from food to oxygen breaking the energy drop to manageable amounts.

31. Concept 9.4 Inside the inner membrane are enzymes called ATP synthase.
- makes ATP from ADP and a phosphate
ATP synthase uses energy from the ion gradient to synthesize ATP.
- proton gradient

32. Concept 9.4

33. Concept 9.4
The ETC is an energy converter that uses the exergonic flow of e- to pump H+ ions across the membrane
- from the matrix to the inner membrane space.
ATP synthases are the only place that are freely permeable to H+

34. Concept 9.4
H+ gradient across a membrane couples the redox rxns. of the ETC to ATP synthesis
- chemiosmosis: connection between the chemical rxn. Makes ATP and transport across a membrane

35. Concept 9.4
H+ ions are pumped by members of the ETC. The resulting gradient is called a proton-motive force: the gradient has the capacity to do work

36. Concept 9.4

37. Concept 9.4 Chemiosmosis is also found in the chloroplasts
- ATP is generated during photosynthesis
- light drives both e- flow down the ETC and H+ gradient formation

38. Concept 9.4 Energy flow during respiration:
Glucose NADH and FADH ETC proton-motive force  ATP
38 ATP formed; 4 from substrate phosphorylation, 34 from oxidative phosphorylation

39. Concept 9.4

40. Concept 9.5
During glycolysis, glucose is oxidized into 2 molecules of pyruvate
- oxidizing agent is NAD+, not oxygen
If no oxygen is present, electrons are transferred from NADH to pyruvate

41. Concept 9.5 Alcohol fermentation: pyruvate  ethanol
- CO2 is released to recycle NAD+
- 2 step process to regenerate NAD+

42. Concept 9.5

43. Concept 9.5 Lactic acid fermentation: pyruvate  lactic acid
- human cells make ATP by (LAF) when oxygen is scarce
- lactate is carried away by blood to the liver; lactate is converted back to pyruvate by liver cells

44. Concept 9.5

45. Concept 9.5
w/out oxygen, the energy still stored in pyruvate is unavailable to cells
Facultative anaerobes: yeasts and bacteria that can make enough ATP to survive using either fermentation or respiration

46. Concept 9.5
Ancient prokaryotes probably used anaerobic fermentation before oxygen was present in the atmosphere
Also, glycolysis does not require mitochondria to occur

47. Concept 9.6
Fats, proteins, and complex carbs can all be used to make ATP
Fats can be broken into monomers
- glycerol can be converted and can enter glycolysis
- fatty acids can be converted into acetyl CoA

48. Concept 9.6

49. Concept 9.6 Proteins must be broken down to amino acids
- various amino acids can be converted as intermediates of glycolysis and the Krebs cycle

50. Concept 9.6
Carbohydrates can be hydrolyzed to form glucose monomers to enter into glycolysis
Metabolism works on supply and demand!!!!

51. Concept 9.6
Carbs and fats can be converted to fats through intermediates of glycolysis and the Krebs cycle
We will store fat even if we have a fat free diet

52. Concept 9.6 Cellular respiration is controlled by feedback mechanisms
Feedback inhibition: end products inhibit the enzymes that catalyze the early steps of the process
Phosphofructokinase (enzyme for step 3 of glycolysis) is the pacemaker