1. CELLULAR RESPIRATION: Harvesting Chemical Energy
Chapter 9

4. CATABOLIC PATHWAYS
Complex molecules that are high in potential energy are broken down into smaller waste products that have less energy
Some of this released energy can later do work, but most is given off as heat
Two major catabolic pathways
Aerobic Respiration
Anaerobic respiration (fermentation)

5. Aerobic (uses oxygen) respiration Exergonic
AEROBIC RESPIRATION
C6H CO2 + 6H20 + energy (ATP and heat)
Aerobic (uses oxygen) respiration
Exergonic
ΔG = -686 kcal/mole of glucose
Big picture – chop up glucose and make ATP
Transfer energy in glucose to ATP
Oxidation of glucose by oxygen

6. ATP (ADENOSINE TRIPHOSPHATE)
The last phosphate of ATP can be removed by enzymes and added to another molecule.
This turns ATP into ADP (adenosine diphosphate).
Molecules that receive a phosphate group have been phosphorylated.
This makes the molecule change shape, which allows the molecule to do work.
After the work is done, the phosphate group is released.

7. Figure 9.2 A review of how ATP drives cellular work

8. REDOX REACTIONS
Oxidation - loss of electrons
Reduction - gain of electrons
In respiration, transferring electrons releases energy to make ATP

9. An e- loses potential energy when it moves from a less electronegative atom toward a more electronegative atom.
In respiration, hydrogen’s electrons are transferred to oxygen (the fall of electrons), which liberates energy.

11. NAD+ Hydrogen atoms are removed gradually from glucose.
They are transferred to oxygen by a coenzyme called NAD+ (nicotinamide adenine dinucleotide).
Dehydrogenase enzymes remove a pair of hydrogen atoms (2 e- and 2 protons) from sugar.
Remember, protons (H+) are hydrogen cations or an H atom without its electron

13. The enzyme delivers 1 proton and 2 e- to its coenzyme NAD+ making NADH.
The remaining proton (H+)is released into surrounding solution.
The e- lose very little energy in this transfer.

14. Figure 9.4 NAD+ as an electron shuttle

15. The three metabolic stages of respiration:
Glycolysis
The Kreb’s cycle
The electron transport chain and oxidative phosphorylation

16. Figure 9.6 An overview of cellular respiration (Layer 3)

17. GLYCOLYSIS: “splitting of sugar”
Occurs in cytoplasm
Series of 10 steps, each with its own enzyme
No oxygen needed (anaerobic)
Needs 2 ATP to start process
Makes 4 ATP by substrate-level phopsphorylation (when an enzyme removes a phosphate from a substrate to make ATP)
Transfers electrons and H+ to NAD+ to make 2 NADH (to go to ETC)

18. Figure 9.7 Substrate-level phosphorylation

19. By the end, one glucose molecule will been broken in half to form two 3-carbon molecules of pyruvate.
Only if oxygen is present, puruvate moves into the Kreb’s cycle (Citric Acid Cycle) to continue aerobic respiration.

20. Figure 9.8 The energy input and output of glycolysis

21. Figure 9.9 A closer look at glycolysis: energy investment phase

22. Figure 9.9 A closer look at glycolysis: energy payoff phase

23. Pyruvate converts to acetyl CoA
Pyruvate enters mitochondria
Pyruvate loses CO2, and the resulting 2-carbon compound is oxidized making acetate.
The e- and H+ are transferred to NAD+ to make NADH (to go to ETC)
Coenzyme A (a vitamin B derivative) attaches to acetate making acetyl CoA

24. Figure Conversion of pyruvate to acetyl CoA, the junction between glycolysis and the Krebs cycle

25. THE KREB’S CYCLE
Acetyl CoA combines with a 4-carbon molecule
This molecule is oxidized over a series of steps that are cyclic
e- and H+ are transferred to NAD+ and FAD+ to make 3 NADH and 1 FADH2 (flavin adenine dinucleotide).
2 molecules of CO2 are given off

26. 1 ATP is made by substrate-level phosphorylation
Only 2 carbons can go through the cycle at one time so the cycle must “turn” twice to oxidize both pyruvates.
CO2 diffuses out of cell, into blood, and is exhaled.
NADH and FADH2 take their electrons to the electron transport chain (ETC)

27. Figure 9.12 A summary of the Krebs cycle

28. Figure 9.11 A closer look at the Krebs cycle

29. ELECTRON TRANSPORT CHAIN
Made up of a chain of molecules embedded in the inner membrane of mitochondria
Mostly proteins with prosthetic groups that can easily donate and accept e- (redox) – many are cytochromes with heme groups (Fe)
NADH transfers e- to first molecule and FADH2 transfers e- to a lower molecule.

30. e- move down the chain via redox reactions
They move down the ETC because oxygen is electronegative and pulls the e- along
Oxygen captures the e- at bottom and along with 2 H+ (from solution) forming water
The energy released by falling e- causes H+ to be pumped out into intermembrane space.

31. H+ move back into mitochondria by diffusion (a proton-motive force) only through a protein called ATP synthase (oxidative phosphorylation)
These protons change ATP synthase’s shape so that it acts as an active site for Pi and ADP to make ATP.
Each NADH eventually yields ~3 ATP.
Each FADH2 eventually yields ~2 ATP.

32. Figure 9.13 Free-energy change during electron transport

33. Figure 9.14 ATP synthase, a molecular mill

34. Figure 9.15 Chemiosmosis couples the electron transport chain to ATP synthesis

35. SUMMARY OF AEROBIC RESPIRATION
Approximately 38 ATP’s made from one glucose
About 60% of energy from glucose is “lost” as heat
This heat helps to keep our warm body temperature

36. Figure Review: how each molecule of glucose yields many ATP molecules during cellular respiration

37. ANAEROBIC RESPIRATION (FERMENTATION)
NO oxygen = anaerobic = no Kreb’s
Alcohol fermentation (yeast)
Pyruvate is converted to ethanol
Lactic acid fermentation (humans)
Pyruvate is converted to lactic acid
2 ATP and 2 NAD+ are made
Makes NAD+ so glycolysis can continue – otherwise NADH has no where to go (without oxygen at bottom of ETC) and is not converted back to NAD+.

38. Figure 9.17a Fermentation

39. Figure 9.x2 Fermentation

40. Figure 9.17b Fermentation

41. Figure 9.18 Pyruvate as a key juncture in catabolism

42. Facultative anaerobes – organisms that make ATP through fermentation if no oxygen and through respiration if oxygen is present (ex. yeast and some bacteria)

43. Evolutionary Significance of Glycolysis
No oxygen required (early earth had no oxygen in atmosphere)
No mitochondria required (prokaryotes do not have)
Most common metabolic pathway

44. Versatility of Respiration
Proteins and lipids enter at different locations than glucose
Intermediates of respiration can be used to make other necessities (like amino acids)
Intermediates and products of respiration inhibit enzymes to slow respiration down.

45. Figure 9.19 The catabolism of various food molecules

46. Figure 9.20 The control of cellular respiration

47. PHOTOSYNTHESIS
Chapter 10

48. BASIC VOCABULARY Autotrophs – producers; make their own “food”
Heterotrophs – consumers; cannot make own food

49. LEAF STRUCTURE
Stomata (stoma) – microscopic pores that allow water, carbon dioxide and oxygen to move into/out of leaf
Chloroplasts – organelle that performs photosynthesis
Found mainly in mesophyll – the tissue of the interior leaf
Contain chlorophyll (green pigment)
Stroma – dense fluid in chloroplast
Thylakoid membrane – inner membrane of chloroplast
Grana (granum) – stacks of thylakoid membrane

50. Figure 10.2 Focusing in on the location of photosynthesis in a plant

51. PHOTOSYNTHESIS SUMMARY
6CO2 + 6H20 + light energy C6H12O6 + 6O2
Converting light energy into chemical energy (using sunlight to make sugar)
Oxygen comes from water, not CO2
Two parts:
Light Reactions
The Calvin Cycle (Dark Reactions or Light Independent)

52. Figure 10.3 Tracking atoms through photosynthesis

53. Figure 10.4 An overview of photosynthesis: cooperation of the light reactions and the Calvin cycle

54. LIGHT Photons – discrete packets of light energy
Chlorophyll a – (blue-green)only pigment that is directly used in light reactions
Chlorophyll b – (yellow-green) accessory pigment
Carotenoids - (yellow-orange)

55. Figure 10.6 Why leaves are green: interaction of light with chloroplasts

56. Figure Evidence that chloroplast pigments participate in photosynthesis: absorption and action spectra for photosynthesis in an alga
Aerobic bacteria gather where there is more oxygen along this algal filament, which was exposed to different colors of light.

57. PHOTOEXCITAION
When photons hit chlorophyll and other pigments, electrons are excited to an orbital of higher energy
In solution when the excited electrons fall, they give off energy (a photon) and fluoresce

58. Figure 10.9 Location and structure of chlorophyll molecules in plants

59. LIGHT REACTIONS Photosystems:
Made of proteins and other molecules surrounding chlorophyll a
Contain a primary electron acceptor
Photosystem I – P700
Photosytem II – P680

60. Figure 10.11 How a photosystem harvests light

61. Noncyclic (predominant route) Cyclic
Require light to occur
Two pathways:
Noncyclic (predominant route)
Cyclic
Noncyclic animation
Another animation

62. NONCYCLIC ELECTRON FLOW
Photosystem II absorbs light
Two electrons excited and captured by primary electron acceptor
“Hole” in photosystem II is filled by 2 electrons that come from the splitting of water
H2O H+ + ½ O2 + 2e-

63. Oxygen is released
Excited electrons pass from primary electron acceptor down an electron transport chain to photosystem I (filling its “hole”)
ATP is made by photophosphorylation as electrons fall down ETC

64. Photons excite 2 electrons from Photosystem I and are captured by its primary electron acceptor
Electrons then move down another ETC to ferredoxin (Fd)
Fd gives electrons to NADP+ (nicotinamide dinucleotide phosphate) making NADPH
The enzyme that helps this transfer of e- is called NADP+ reductase

65. Figure 10.12 How noncyclic electron flow during the light reactions generates ATP and NADPH

66. Figure 10.13 A mechanical analogy for the light reactions

67. Figure 10.14 Cyclic electron flow

68. CYCLIC ELECTRON FLOW Only Photosystem I is used
Fd passes electrons back to Photosystem I via ETC
Some ATP made
No NADPH made
No oxygen released
Used when cell needs more ATP than NADPH

69. ETC MITOCHONDRIA CHLOROPLAST
Food (chemical energy) to ATP (chemical energy)
ATP synthase
Pumps H+ into intermembrane space
Light energy to ATP (chemical energy)
ATP synthase
Pumps H+ into thylakoid space

70. Figure 10.15 Comparison of chemiosmosis in mitochondria and chloroplasts

71. Figure 10.17 The Calvin Cycle

72. CALVIN CYCLE
Also called Dark Reactions because light is not needed; however products from light reactions are needed.
Carbon Fixation – initial incorporation of carbon into organic molecules
CO2 attaches to a 5-carbon sugar called ribulose bisphosphate (RuBP)
The enzyme that catalyzes this is called rubisco
Calvin cycle animation

73. One G3P molecule leaves cycle to be used by plant
Immediately splits into two 3-carbon molecules called 3-phosphoglycerate
3-phosphoglycerate is phosphorylated by ATP (from light reactions) making ,3-bisphosphoglycerate
1,3-bisphosphoglycerate is reduced by taking electrons from NADPH making glyceraldehyde 3-phosphate (G3P)
One G3P molecule leaves cycle to be used by plant
The remaining G3P’s are converted into RUBP in several steps and by getting phosphorylated by ATP
3 phosphoglycerate and 1-3 bisphosphoglycerate from glycolysis

74. Recall, G3P is the sugar formed by splitting glucose in glycolysis
G3P can be made into glucose, sucrose, cellulose etc. by plant

75. C3 PLANTS – have a problem
Examples : rice, wheat, and soy beans
Problem - produce less food when stomata are closed during hot days because low CO2 starves Calvin Cycle and rubisco can accept O2 instead of CO2
High oxygen levels = O2 passed to RUBP (not CO2) and Calvin cycle stops
When this oxygen made product splits, it makes a molecule that is broken down by releasing CO2

76. This process is called photorespiration.
Occurs during daylight (photo)
Uses O2 and makes CO2 (respiration)
NO ATP made (unlike respiration) and NO food made
Early earth had low O2 when first plants appeared so this would not have mattered as much
Photorespiration drains away as much as 50% of carbon fixed by Calvin Cycle in many plants.

77. C4 PLANTS – have a solution
Examples: sugarcane, corn and grasses
Leaves contain bundle-sheath cells and mesophyll cells
Bundle sheath surrounds veins of leaf (location of Calvin cycle)
Mesophyll – between bundle and surface

78. In mesophyll cells: CO2 fixed to phosphoenolpyruvate (PEP)
PEP carboxylase is the enzyme that does this
PEP carboxylase has higher affinity for CO2 than rubisco so less danger of O2 interfering
The fixed CO2 is then taken to Calvin cycle (in bundle-sheath) as part of a 4-carbon molecule (malate)
Malate gives CO2 to Calvin cycle
PEP from glycolysis
Malate and oxaloacetate from Krebs

79. Figure 10.18 C4 leaf anatomy and the C4 pathway
Malate and oxaloacetate from Krebs

80. CAM PLANTS – have another solution (crassulacean acid metabolism)
Examples: succulent plants (pineapples and cacti etc.)
Open stomata at night and close during day
At night CO2 is fixed into organic acids in mesophyll and then taken to Calvin cycle (also in mesophyll) during day.

81. Figure 10.19 C4 and CAM photosynthesis compared

82. PHOTOSYNTHESIS FACTS
50% of organic material made is used by plant in respiration
Organic molecules often leave leaves as sucrose
Large amounts of cellulose are made (for cell walls)
“And no process is more important than photosynthesis to the welfare of life on Earth.” (Campbell and Reece, 2005)
Photo makes ~160 billion metric tons of carbohydrate per year (1 metric ton = ~1.1 tons)
This equals about 60 trillion copies of this book in terms of organic material.
This equals 17 stacks of this book going to from the earth to the sun (~93 mill miles)

83. Figure 10.20 A review of photosynthesis

84. Carbon Cycle

85. Carbon Cycle Human Impact on C Cycle Climate change = global warming
Increased levels of CO2 (and some other gases) increase Greenhouse effect (traps heat)
Increased Greenhouse Effect equals warming earth
How does deforestation and burning fossil fuels impact the carbon cycle?