1. PowerLecture: Chapter 7
Where It Starts - Photosynthesis

2. Sunlight and Survival
p.107

3. Photons Packets of light energy
Each type of photon has fixed amount of energy

4. Visible Light Violet (380 nm) to red (750 nm)
Longer wavelengths, lower energy
Figure 7-2 Page 108

5. Visible Light Fig. 7-2, p.108 shortest wavelengths (most energetic)
range of most radiation
reaching Earth’s surface
range of heat escaping
from Earth’s surface
longest wavelengths
(lowest energy)
gamma rays x
rays
ultraviolet
radiation
near-infrared
radiation
infrared
radiation
radio
waves
microwaves
VISIBLE LIGHT
400
450
500
550
600
650
700
Wavelengths of light (nanometers)
Fig. 7-2, p.108

6. Pigments
Light-catching part of molecule often has alternating single and double bonds
Electrons in these bonds move to higher energy levels by absorbing light

7. Variety of Pigments Chlorophylls a and b Carotenoids Anthocyanins
Phycobilins

8. Wavelength absorption (%) Wavelength (nanometers)
Chlorophylls
Main pigments in most photoautotrophs
Wavelength absorption (%)
chlorophyll a
chlorophyll b
Wavelength (nanometers)

9. Accessory Pigments Carotenoids, Phycobilins, Anthocyanins
beta-carotene
phycoerythrin (a phycobilin)
percent of wavelengths absorbed
wavelengths (nanometers)

10. Pigments
Fig. 7-3a, p.109

11. Pigments
Fig. 7-3b, p.109

12. Pigments
Fig. 7-3c, p.109

13. Pigments
Fig. 7-3d, p.109

14. Pigments
Fig. 7-3e, p.109

15. Pigments in Photosynthesis
Bacteria
Pigments in plasma membranes
Plants
Pigments and proteins organized into photosystems embedded in thylakoid membrane

16. T.E. Englemann’s Experiment
Background
Certain bacteria move toward areas of high oxygen concentration

17. T.E. Englemann’s Experiment

18. Photosynthesis Equation
LIGHT ENERGY
12H2O + 6CO2
6O2 + C6H12O6 + 6H2O
Water
Carbon Dioxide
Oxygen
Glucose
Water
In-text figure Page 111

19. Photosynthesis
Fig. 7-6a, p.111

20. Photosynthesis two outer membranes thylakoid compartment
thylakoid membrane system inside stroma
stroma
Fig. 7-6b, p.111

21. light-dependant reactions light-independant reactions
Photosynthesis
SUNLIGHT
H2O O2
CO2
NADPH, ATP
light-dependant reactions
light-independant reactions
NADP+, ADP
sugars
CHLOROPLAST
Fig. 7-6c, p.111

22. Light-Dependent Reactions
Pigments absorb light energy, give up e-, which enter electron transfer chains
Water molecules split, ATP and NADPH form, and oxygen is released
Pigments that gave up e- ‘s get replacement e- ‘s

23. Light-Dependent Reactions
photon
Photosystem
Light-Harvesting Complex
Fig. 7-7, p.112

24. cross-section through a disk-shaped fold in the thylakoid membrane
LIGHT-
HARVESTING
COMPLEX
PHOTOSYSTEM II
sunlight
PHOTOSYSTEM I H+
NADPH e- e- e- e- e- e-
NADP + + H+ e-
H2O H+ H+ H+ H+
thylakoid
compartment H+ H+ H+ H+ H+ H+ O2 H+
thylakoid
membrane
stroma
ADP + Pi
ATP
cross-section through a disk-shaped fold in the thylakoid membrane H+
Fig. 7-8, p.113

25. Photosystem Function: Harvester Pigments
Most pigments in photosystem are harvester pigments
When excited by light energy, these pigments transfer energy to adjacent pigment molecules
Each transfer involves energy loss

26. Photosystem Function: Reaction Center
Energy is reduced to level that can be captured by molecule of chlorophyll a
This molecule (P700 or P680) is the reaction center of a photosystem
Reaction center accepts energy and donates electron to acceptor molecule

27. Electron Transfer Chain
Adjacent to photosystem
Acceptor molecule donates electrons from reaction center

28. Noncyclic Electron Flow
Two-step pathway for light absorption and electron excitation
Uses two photosystems: type I and type II
Produces ATP and NADPH
Involves photolysis (splitting of water)

29. Machinery of Noncyclic Electron Flow
H2O
second electron transfer chain
photolysis e– e–
ATP SYNTHASE
first electron transfer chain
NADP+
NADPH
ATP
PHOTOSYSTEM II
PHOTOSYSTEM I
ADP + Pi

30. Cyclic Electron Flow
Happens when excess NADPH backs up the Photosystem II
Electrons
are donated by P700 in photosystem I to acceptor molecule
flow through electron transfer chain and back to P700
No NADPH is formed

31. Chemiosmotic Model of ATP Formation
Electrical and H+ concentration gradients are created between thylakoid compartment and stroma
H+ flows down gradients into stroma through ATP synthase
Flow of ions drives formation of ATP

32. Chemiosmotic Model for ATP Formation
H+ is shunted across membrane by some components of
the first electron transfer chain
Gradients propel H+ through ATP synthases;
ATP forms by phosphate-group transfer
Photolysis in the thylakoid compartment splits water
H2O e–
acceptor
ATP SYNTHASE
ATP
ADP + Pi
PHOTOSYSTEM II

33. Light-Independent Reactions
“Sugar Factory” part of photosynthesis
Take place in the stroma
Includes the Calvin-Benson cycle

34. THESE REACTIONS PROCEED IN THE CHLOROPLAST’S STROMA
Calvin- Benson Cycle
THESE REACTIONS PROCEED IN THE CHLOROPLAST’S STROMA
Fig. 7-10a, p.115

35. Calvin-Benson Cycle Overall reactants Overall products Carbon dioxide
ATP
NADPH
Overall products
Glucose
ADP
NADP+
Reaction pathway is cyclic and RuBP (ribulose bisphosphate) is regenerated

36. unstable intermediate6
CO2 (from the air)
Calvin- Benson Cycle
CARBON FIXATION 6 6
RuBP
unstable intermediate 12
PGA
6 ADP 12
ATP 6
ATP 12
NADPH
4 Pi
12 ADP
12 Pi
12 NADP+ 10
PGAL 12
PGAL 2
PGAL Pi P
glucose

37. phosphorylated glucose
Calvin- Benson Cycle
6CO2
ATP
6 RuBP
12 PGA 12
6 ADP
12 ADP +
Calvin-Benson
cycle
12 Pi
ATP 12
NADPH
4 Pi
12 NADP+
10 PGAL
12 PGAL
1 Pi 1
phosphorylated glucose
Fig. 7-10b, p.115

38. The C3 Pathway
In Calvin-Benson cycle, the first stable intermediate is a three-carbon PGA
Because the first intermediate has three carbons, this is called the C3 pathway

39. Hot Dry days & C3 Plants On hot, dry days stomata close Inside leaf
Oxygen levels rise
Carbon dioxide levels drop
Rubisco attaches RuBP to oxygen instead of carbon dioxide (this is photorespiration)
Only one PGAL forms instead of two - slowing sugar formation

40. C3 Plants
Fig. 7-11a1, p.116

41. C3 Plants upper epidermis palisade mesophyll spongy mesophyll lower
stoma
leaf vein
air space
Basswood leaf, cross-section.
Fig. 7-11a2, p.116

42. Twelve turns of the cycle, not just six, to
C3 Plants
Stomata closed: CO2 can’t get in; O2 can’t get out
Rubisco fixes oxygen, not carbon, in mesophyll cells in leaf
RuBP
6 PGA glycolate
Calvin-Benson
Cycle
5 PGAL
6 PGAL
CO2
+ water
1 PGAL
Twelve turns of the cycle, not just six, to
make one 6-carbon sugar
Fig. 7-11a3, p.117

43. C4 Plants
Fig. 7-11b1, p.117

44. C4 Plants in hot dry weather
Carbon dioxide is fixed twice
In mesophyll cells, carbon dioxide is fixed to form four-carbon oxaloacetate
Oxaloacetate is transferred to bundle-sheath cells
Carbon dioxide is released and fixed again in Calvin-Benson cycle

45. C4 Plants upper epidermis mesophyll cell bundle- sheath cell lower
Corn leaf, cross-section.
Fig. 7-11b2, p.117

46. C4 Plants Stomata closed: CO2 can’t get in; O2 can’t get out
Carbon fixed in the mesophyll cell, malate diffuses into adjacent bundle-sheath cell
PEP
oxaloacetate
C4 Plants
C4 cycle
malate
pyruvate
CO2
In bundle-sheath
cell, malate gets converted to pyruvate with release of CO2, which enters Calvin-Benson cycle
RuBP
12 PGA…?
Calvin-Benson
Cycle
10 PGAL
12 PGAL
2 PGAL
1 sugar
Fig. 7-11b3, p.117

47. CAM Plants Carbon is fixed twice (in same cells) Night Day
Carbon dioxide is fixed to form organic acids
Day
Carbon dioxide is released and fixed in Calvin-Benson cycle

48. CAM Plants
Fig. 7-11c1, p.117

49. CAM Plants stoma epidermis with thick cuticle mesophyll cell air space
Fig. 7-11c2, p.117

50. Stomata stay closed during day, open for CO2 uptake at night only.
CAM Plants
Stomata stay closed during day, open for CO2 uptake at night only.
C4 cycle operates at night when CO2 from aerobic respiration fixed
C4 CYCLE
CO2 that accumulated overnight used in C3 cycle during the day
Calvin-Benson
Cycle
1 sugar
Fig. 7-11c3, p.117

51. Photosynthesis overview sunlight Light- Dependent Reactions 12H2O 6O2
ADP + Pi
ATP
NADPH
NADP+
6CO2
Calvin-Benson cycle
6 RuBP
12 PGAL
Light-
Independent
Reactions
6H2O
phosphorylated glucose
end products (e.g., sucrose, starch, cellulose)
Fig. 7-14, p.120

52. Carbon and Energy Sources
glucose (stored energy, building blocks)
sunlight energy
Photosynthesis
Aerobic Respiration
1. H2O is split by light energy. Its oxygen diffuses away; its electrons, hydrogen enter transfer chains with roles in ATP formation. Coenzymes pick up the electrons and hydrogen
1. Glucose is broken down completely to carbon dioxide and water. Coenzymes pick up the electrons, hydrogens.
oxygen
2. The coenzymes give up the electrons and hydrogen atoms to oxygen-requiring transfer chains that have roles in forming many ATP molecules.
2. ATP energy drives the synthesis of glucose from hydrogen and electrons (delivered by coenzymes), plus carbon and oxygen (from carbon dioxide).
carbon dioxide,water
ATP available to drive nearly all cellular tasks
Fig. 7-12, p.118

53. Fig. 7-16b, p.121