Carbon Fixation Flashcards
how are 3C intermediates made?
- degradation of larger molecules
- carbon fixation in plants
carbon fixation cycle
calvin cycle
key intermediate
ribulose 1,5 - bisphosphate (RuBP) constantly regenerate
net result
CO2 reduction with NADPH
3 stages of Calvin cycle
- CO2 fixation
- reduction
- RuBP regeneration
main enzyme
Mg dependent rubisco w/ dual activity: carboxylation and oxygenation (competing processes)
- 8 small and 8 large subunits
Step 1: Fixation
RuBP and CO2 –> 2 3-phosphoglycerate
Step 2: reduction
3-phosphoglycerate reduced to glyceraldehyde 3-phosphate using NADPH and ATP
Step 3: RuBP regeneration
important
Rubisco oxygenase reaction
photorespiration
- rubisco reacts with O2 instead of CO2 making 3-phosphoglycerate and phosphoglycolate (catalytic imperfection)
C2 pathway (glycolate pathway)
- ATP consuming
- C2 fragment recovery from photorespiration
- 2 phosphoglycolates converted to Ser + CO2
C3 Photosynthesis disadvantages
- water loss
- photorespiration
CAM Plants
captures CO2 at night and fixed to oxaloacetate via PEPCK; oxaloacetate is reduced to malate which releases CO2 in the daytime to resume with CO2 fixation in the day
C4 Plants
bypass C3 step by fixing CO2 into a C4 compound which is delivered to bundle sheath cells in form of malate
CAM C4 advantages
Water conservation
Reduced photorespiration
C3 vs C4
C4 grow better in hot climates
C3 have advantage in cooler climate due to lower energy use
