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Photosynthesisand some generally interesting facts about plants and whatnot
Biophysical Seminar2011. December 2.
Bence FerdinandyPhysics MSc II.
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
Introduction
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
Introduction
Light phase
• binding of energy• emission of oxigen
Dark phase
• binding of CO2
• sugar synthesis
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
Outline of the talk
• The anatomy of Photosynthesis
• The Light phase
• The Dark phase
• Problems: photorespiration
• The efficiency of photosynthesis
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
The plant cell (EM pic)
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
The plant cell (cartoon)
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
Endosymbiothic theory
Our ancestor protista ate bacteria like things: mithochondria and chloroplast
Evidence:• double membrane
• own DNA
• lot of things similar to bacteria
• they replicate separately (we get our mother’s)
We are not alone in our own cells!
Shocking piece of information
Bence Ferdinandy – Biophysics Seminar 2011. december 2..
Chloroplast (EM pic)
MP
Grana (thylakoid membrane)
Lamella (thylakoid membrane)
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
Chloroplast (cartoon)
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
Purpose of the light phase:high energy molecules
ATP: Adenosine triphosphate
NADPH: Nicotinamide adenine dinucleotide phosphate
Very important, (almost) everything works with it. Made in mitchondria also.
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
Light phase I. (the electron transportchain)
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
Light phase I. (the electron transportchain)
„OUTSIDE”
„INSIDE”
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
Light phase I. (the electron transportchain)
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
The heart of it all: the Photosystem
What happens here?
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
Photosystem II
Quite a beauty if ya ask me.
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
The light harvesting complex of the Photosystems
The harvesting complex:Energy transfer with FRET
Chlorophyll-A molecule
Special pair
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
One photon excites one electron
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
The electron is passed to a plastoquinoneOne PQ can take two electrons
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
Plastoquinone takes up two protons from the stroma („outside”)
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
Plastoquinone gives the two electrons to cytochrome
And the two protons to the lumen („inside”)
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
PSII lost two electrons: it splits water to get electrons, one H2O = e-
2 H2O = O2 + 2 p+ -> more protons „inside”
Risky!
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
Cytochrome transfers the two electrons to plastocyanin
Two more protons are pumped to the lumen („inside”)
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
Plastocyanin takes the two electrons to PSIThe electrons are now ground state: their energy lost in the transfer and proton pumping
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
Electrons are excited again and transfered to the the Ferredoxin NADP Reductase by ferredoxin
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
The FNR puts the energy of the electrons into NADPH
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
Now there’s a concentration gradient of protons, so the protons go back „outside” through the ATP synthase.
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
The energy of the gradient is stored in ATP.
ATP synthase is like a turbine and is rotated by the proton flow.
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
Light phase II.
Bence Ferdinandy – Biophysics Seminar 2011. december 2..
Light phase III.
2 H2O , 4 photons
2 NADPH , 3 ATP , 1 O2
12 protons pumped
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
Absortion spectrum of chlorophyll
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
Excitation levels of chlorophyll
S0
S1
S2
S3
T1
light
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
Excitation levels of chlorophyll
S0
S1
S2
S3
T1
light
Fast energy loss
photosynthesis
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
Excitation levels of chlorophyll
S0
S1
S2
S3
T1
light
Fast energy loss
photosynthesis
Fluorescence
Phosphorescence
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
Dark phase I: RuBisCO
Ribulose-1,5-bisphosphate carboxylase oxygenase:
The most abundant protein on Earth.
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
Dark phase II: Calvin-cycle
• RuBisCO + 3 RuBP (5C) + 3 CO2 3 pc. 6C 6 pc. 3PGA (3C)
• 13 steps, energy consuming process (Calvin cycle) 1 G3P (3C) 3 RuBp
• 2 G3P 1 glucose (6C)
• the energy used during this: 12 NADPH 18 ATP
24 photons
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
Calvin cycle
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
Photorespiration
• RuBisCO can take O2 as substrate, creates useless product (concentration dependent)
• reversing the product needs energy, process loses C
• it is done by the photorespiration complex (chloroplast + mitochondrion + peroxisome)
• types of photosynthesis: C3, C4, CAM
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
C3 Photosynthesis
• Typical (85%)
• Just explained how it works
• Fixes CO2 into C3 product
• Inefficient in hot and dry circumstances, because leaves „close” (don’t lose water, can’t take up CO2
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
C4 Photosynthesis
• Spatial separation
• Fixes CO2 in outer cell with PEP (another ensym) to C4 product
• C4 into CO2 in inner cell
• Calvin cycle in inner cell
• RuBisCo doesn’t meet high concentration of oxygen
• Example: sugarcane, corn
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
CAM Photosynthesis
• Temporal separation, 1 cell
• Fixes CO2 with PEP during nightwhile Calvin cycle is not going
• Closes cell during day and does Calvin cycle
Example: Cactus, pineapple
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
Efficiency I.
Loses of energy during the whole process: • ~30% - cross section
• ~47% - limited absorbtion range
• ~24% - uses energy of red quanta only
• ~68% - during the glucose production
• ~35-45% - photorespiration and such
this estimate gives 5-6% efficiency
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
Efficiency II.
• Theoretical: 30% (including the energy loss of chemical reactions
• Laboratory conditions: 25%
• Natural conditions:• in Death Valley (winter evening primrose): 8%• sugarcane: 7% (remember, it’s C4)• most crops: 1-4 %
• This 1-7% is also used to upkeeping, growing, reproduction
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
Efficiency III.
Comparison with solar panels:
• theoretical: 86%
• laboratory: > 40 %
• commercial (cheap/not so cheap): ~6% / 15-20%
BUT: the plant is a self-replicating, self-maintaining solar cell, and enviroment friendly (no rare elements needed)
Bence Ferdinandy – Biophysics Seminar 2011. december 2.
What we have learned
• the anatomy of the photosynthetic apparatus: chloroplast
• light phase: electron transport chain, water splitting, O2 making
• generates high energy molecules, uses proton gradient
• dark phase: CO2 fixation with RuBisCO + energy = glucose
• photorespiration: RuBisCO can fix O2 as well -> C3, C4, CAM paths
• efficiency: below 10%