photosynthesis and some generally interesting facts about plants and whatnot biophysical seminar...
TRANSCRIPT
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%