Photosynthesis and some generally interesting facts about plants and whatnot Biophysical Seminar...

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

Light phase

• binding of energy• emission of oxigen

Dark phase

• binding of CO2

• sugar synthesis

Outline of the talk

• The anatomy of Photosynthesis

• The Light phase

• The Dark phase

• Problems: photorespiration

• The efficiency of photosynthesis

The plant cell (EM pic)

The plant cell (cartoon)

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)

Grana (thylakoid membrane)

Lamella (thylakoid membrane)

Chloroplast (cartoon)

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.

Light phase I. (the electron transportchain)

„OUTSIDE”

„INSIDE”

The heart of it all: the Photosystem

What happens here?

Photosystem II

Quite a beauty if ya ask me.

The light harvesting complex of the Photosystems

The harvesting complex:Energy transfer with FRET

Chlorophyll-A molecule

Special pair

One photon excites one electron

The electron is passed to a plastoquinoneOne PQ can take two electrons

Plastoquinone takes up two protons from the stroma („outside”)

Plastoquinone gives the two electrons to cytochrome

And the two protons to the lumen („inside”)

PSII lost two electrons: it splits water to get electrons, one H2O = e-

2 H2O = O2 + 2 p+ -> more protons „inside”

Risky!

Cytochrome transfers the two electrons to plastocyanin

Two more protons are pumped to the lumen („inside”)

Plastocyanin takes the two electrons to PSIThe electrons are now ground state: their energy lost in the transfer and proton pumping

Electrons are excited again and transfered to the the Ferredoxin NADP Reductase by ferredoxin

The FNR puts the energy of the electrons into NADPH

Now there’s a concentration gradient of protons, so the protons go back „outside” through the ATP synthase.

The energy of the gradient is stored in ATP.

ATP synthase is like a turbine and is rotated by the proton flow.

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

Absortion spectrum of chlorophyll

Excitation levels of chlorophyll

Fast energy loss

photosynthesis

Fast energy loss

photosynthesis

Fluorescence

Phosphorescence

Dark phase I: RuBisCO

Ribulose-1,5-bisphosphate carboxylase oxygenase:

The most abundant protein on Earth.

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

Calvin cycle

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

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

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

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

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

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

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)

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%

Photosynthesis and some generally interesting facts about plants and whatnot Biophysical Seminar...

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