Photosynthesis: Introduction
CO2
H2O
light
carbohydrate
O2
6CO2 + 6H2O C6H12O6 + 6O2
Photosynthesis is the initial source of energy for almost all biological activities
Light
Heat
ADPNADP+
NADPHATP
C(H2O)O2
CO2H2O
CO2H2O
C(H2O)O2
ADPNAD+
NADHATP
SynthesisMovementIon pumpsGrowthReproduction
Photosynthesis: plants,photosynthetic bacteria
Respiration: plants,animals, bacteria, etc.
Compare photosynthesis to respiration: Respiration: C6H12O6 + 6O2 6CO2 + 6H2O
Go’ = -2840 kJ/mol Photosynthesis in green plants: 6CO2 + 6H2O C6H12O6 + 6O2
Go’ = +2840 kJ/mol Unfavorable Go’ explains the need for energy input. That is the role of light.
In higher plants, photosynthesis occurs in chloroplasts
The aquatic plant, Elodea You may see dark grana inside some chloroplasts.
Chloroplast ofZea mays
Under an electron microscope, chloroplasts have amore complex structure.
stroma grana lamellae stroma lamellae
The concentration of grana varies among chloroplasts.
Chloroplast ofPisum sativum
Photosynthesis occurs ingreen plants,cyanobacteria,and some other bacteria
Photosynthesis as described earlier: 6CO2 + 6H2O C6H12O6 + 6O2
Oxidation of D in H2D; reduction of C and O in CO2
Compare photosynthesis in plants and bacteria
Plants (divided by 6, H2O added to each side) CO2 + 2 H2O C(H2O) + O2 + H2O
Green sulfur bacteria CO2 + 2 H2S C(H2O) + 2S + H2O
Purple non-sulfur bacteria CO2 + 2 CH3CHOHCH3 C(H2O) + 2 CH3COCH3 + H2O isopropanol acetone CO2 + 2 CH3CHOHCOOH C(H2O) + 2 CH3COCOOH + H2O lactate pyruvate
Generalize: CO2 + 2 H2D C(H2O) + 2 D + H2O D = H/electron donor
How to measure photosynthesis
Starch production
Van Helmont (1577-1644): A willow that grew for 5 years in acontainer gained more than a half centner in weight (ca 60 lbs), whereas the soil lost only 2 ounces.
Illuminated leaves can be boiled in ethanol (to break membranes),then stained for starch with iodine.
6CO2 + 6H2O C6H12O6 + 6O2
How to measure photosynthesis
Starch production
Potato starch visualized by light microscopy…with a light iodine stain under polarized light
6CO2 + 6H2O C6H12O6 + 6O2
How to measure photosynthesis
O2 production
Priestly (1733-1804): Green plants give off oxygen and thus improvethe air.
Engelmann (1843-1909): produced the first action spectrum of photo-synthesis using Spirogyraalgae and aerotactic (oxygen-sensing) bacteria.
6CO2 + 6H2O C6H12O6 + 6O2
How to measure photosynthesis
CO2 uptake
Amoroso et al. Plant Physiol. 116:193 (1998)
6CO2 + 6H2O C6H12O6 + 6O2
How to measure photosynthesis
Dye bleaching (DCPIP reduction; Hill reaction)
(ZZZ = e- transport inhibitor)
blue colorless
Light on
Photosynthesis as described earlier: 6CO2 + 6H2O C6H12O6 + 6O2
Oxidation of D in H2D; reduction of C and O in CO2
Compare photosynthesis in plants and bacteria
Plants (divided by 6, H2O added to each side CO2 + 2 H2O C(H2O) + O2 + H2O
Green sulfur bacteria CO2 + 2 H2S C(H2O) + 2S + H2O
Purple non-sulfur bacteria CO2 + 2 CH3CHOHCH3 C(H2O) + 2 CH3COCH3 + H2O isopropanol acetone CO2 + 2 CH3CHOHCOOH C(H2O) + 2 CH3COCOOH + H2O lactate pyruvate
Generalize: CO2 + 2 H2D C(H2O) + 2 D + H2O D = H/electron donor
Oxidation of D in H2D; reduction of C and O in CO2
These reactions are separable. Dye bleaching, which occurswith O2 production, shows that the oxidation of H2O (or H2S,etc.) does not depend on the reduction of CO2
2 DCPIP (blue) + 2 H2O 2 DCPIPH2 (colorless) + O2
In the bacterial and plant photosynthetic reactions,
CO2 + 2 H2D C(H2O) + 2 D + H2O
The separate reactions are,
2 H2D light 2 D
2 NADP+ 2 NADPH + H+ 3 ADP + 3 Pi 3 ATP
C(H2O) + H2O (dark) CO2
The light reactions produce H. (reductant) and energy.
Summary
The reaction of photosynthesis can be summarized as:6CO2 + 6H2O C6H12O6 + 6O2or better,6CO2 + 12H2O C6H12O6 + 6H2O + 6O2
But the product is starch, not C6H12O6
Photosynthesis can be measured as starch production, O2production, CO2 uptake, or dye reduction
The oxidation of H2O and the reduction of CO2 are separable
If a sample of algae, when illuminated, releases 3 x 10-5
mol O2/min, how rapidly will it incorporate CO2? How muchstarch will be formed per minute? How many photons of lightwill be needed per minute?