Biology 1002B Lecture Notes - Lecture 9: Glyceric Acid, Photosynthesis, Photorespiration

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18 Apr 2012
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Lecture 9 - Photosynthesis II (7.3-7.5)
Global CO2 Fixation (105 Gt/year) Gt=Gigatons
Terrestrial 56.4 Gt
Oceanic 48.5 Gt
o Single-celled phytoplankton responsible for oceanic fixation
Are ectotherms, usually grow faster where its warm, slower where its cold
Near the equator there’s no phytoplankton even though its warm. Why?
Less dissolved gas (CO2) (not main reason)
Part of a food web (animals consuming phytoplankton) (not main reason)
Nutrients (low iron near equator) (main reason)
o Need iron for cofactors etc.
o Colder areas (Arctic) have more iron, hence more phytoplankton
o Experiment
Dumping iron into water bodies near the equator
More phytoplankton growth
Calvin Cycles
Set of reactions that are pulling CO2 out of the atmosphere
Takes place in strom enzymes in the stroma catalyze fixation of CO2
3 Phases
o Carboxylation reaction
RuBP + CO2 PGA: initial step
o Reduction
NADPH & ATP
o Regeneration
RuBP produced again
Endergonic
o Need ATP from light reactions
o Needs reducing power NADPH from light reactions
Substrate
o Ribulose Biphosphate (RuBP) (enzyme, 50% of all plant enzymes, most abundant
enzyme in plants)
5 carbon sugar phosphate on each end
o 1 molecule of RuBP reacts with 1 CO2
o Three cycles (three molecules of RuBP & 3 CO2) 1 G3P produced
First stable product
o 3-Phospho-Glycerate (PGA) (3 means 3 carbons)
o 3 cycles 6 PGA produced
6 ATP incorporated into cycle
o Driving reduction
6 NADPH incorporated into cycle
o Reducing power to produce (G3P)
6 molecules of Glyceraldehyde-3-Phosphate (G3P) in 3 cycles
1 molecule of G3P is removed from the cycle and produced as a product in 3 cycles
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o 2 G3P combine to produce 6 glucose (6 cycles needed to produce 1 molecule of
glucose)
15 carbons left over are regenerated into RuBP
Every photosynthetic organism on planet carries out Calvin cycle
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