chapter 7 photosynthesis: the light reactions
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Chapter 7 Photosynthesis: The light reactions. synthesis using light is the only process of biological system that can harvest sunny energy. a deceptively simple equation 6 C O 2 + 6 H 2 O C 6 H 12 O 6 + 6 O 2 - PowerPoint PPT PresentationTRANSCRIPT
Chapter 7 Photosynthesis: The light reactions
synthesis using light
is the only process of biological system that can harvest sunny energy. a deceptively simple equation 6 CO2 + 6 H2O C6H12O6 + 6 O2
stored energy can be used to power other cellular processes in the plant and provide the energy source for all forms of life. Topics: the characteristics of light, the structure of the photosynthetic apparatus, the processes of chlorophyll excitation, the synthesis of ATP and NADPH.
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Light: a wave and a particle
* c (the speed of wave) =λν
* E (the energy of photon)= hν
h : Planck’s constant (6.62 × 10-34 Js)
* Quantum (quanta)
each photon contains an amount of energy
discontinuous
Electromagnetic spectrum
Sunlight like a rain of photons of different frequencies.
UV-A: 320 – 400 nm
UV-B: 280 – 320 nm
UV-C : 290 nm
Light emitting diode (LED)
blue 470 nm
red 660 nm
Absorption spectrum: the amount of light energy taken up or absorbed by a molecule or
substance as a function of the light wavelength of the light.
green
Action spectrum 光譜 :the magnitude of a response of a biological system to light,
as a function of wavelength
Light-induced phenomenon
Carotenoid absorption:
400 ~500 nm
→ the pigment responsible for the particular light-induced phenomenon
O2 evolved
Late 1800s
Photosynthetic pigments:
porphyrin-like group
accessory pigments
cyanobacteria
red algae
Chl a, b, c, dxanthophyll
phytol chain
2. Chlorophyll a in nonpolar solvent
3. Chlorophyll b in nonpolar solvent
4. Phycoerythrobilin in an aqueous buffer
5. β-carotene in nonpolar solvent
Light absorption and emission by chlorophyll
1. heat loss; 2. fluorescence;
3. energy transfer; 4. photochemistry.
Chl + h → Chl* (10-9s), discontinuous
Light energy Chemical energy
Antenna天線 complex: collect light and physical resonance transfer, no chemical reactions; high efficiency of energy transfer.
Reaction center: the chemical oxidation and reduction reactions leading to long-term energy storage take place.
pigments,
e- transfer proteins
more efficiency
Chl b Chl a
Core/peripheral
The antenna funnels 注入 energy to the reaction center— fluorescene resonance energy transfer
λmax of Chl b: 650 nm
Chl a: 670 nm
red shif
A physical phenomenon
directionality and irreversibility
p. 138
1932 Emerson and Arnold
oxygen production vs. flash energy
– a suspension of Chlorella pyrenoidosa
– 10-5 s flash, 0.1 s apart
– varied light intensity 強度 ,
slope
saturation
many chlorophyll molecules
involve in energy conversion
during photosynthesis
– Quantum yield () No. of photochemical products / Total No. of quanta absorbed 0.1 for O2 production
Quantum requirement
10 for O2 evolution
– Quantum efficiency 量子效率≒ 1
engage in photochemistry / absorbed photons
– Energy efficiency 0.25≒ the stored energy of chemical compound / the energy of absorbed photons
CO2 + H2O light (CH2O) + O2 G = 467 kJ/mol
red light: 467×103/10 ×17.1×104
blue light: 467×103/10 ×23.95×104
E = hν
O2/10 photons
EE
low
Hill reaction (1937)
an artificial electron acceptors in isolated chloroplast thylakoid
No CO2 condition, still O2 production
4 Fe3+ + 2 H2O → 4 Fe2+ + O2 + 4 H+
CO2 + 2 H2S → (CH2O) + 2 S + H2O H2
18O + CO2 → (CH2O) + 18O2
(1) CO2 + 2 H2O → (CH2O) + O2 + H2O
(2) CO2 + H2O → (CH2O) + O2
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[In eukaryotic photosynthetic organisms, the reaction centers and most
of the antenna complexes are integral within the membrane of
chloroplast; in photosynthetic prokaryotes, the site of photosynthesis is
the plasma membrane or membranes derived from it. P. 132]