BIOL1006 Lecture Notes - Lecture 1: Glycolysis, Pyruvic Acid, Carboxylation

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25 Jun 2016

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Lecture 1
Calvin cycle - aka C3 photosynthesis
creates organic molecules from CO2
uses ATP (from cyclic/noncyclic photophosphorylation) to power
endergonic reactions
uses reducing power of NADPH to attach H to C atoms
carbon fixation - CO2 binds to ribulose 1,5-biphosphate (RuBP)
RuBP - 5-carbon sugar made from reassembling bonds of fructose 6-
phosphate and glyceraldehyde 3-phosphate
forms 2 molecules of 3-phosphoglycerate (PGA)
process catalyzed by rubisco (ribulose biphosphate
3 CO2 + 9 ATP + 6 NADPH + water >> glyceraldehydes 3-phosphate
+ 8 P + 9 ADP + 6 NADP+
w/ 3 turns of Calvin cycle, 3 CO2 enters, 3 RuBP regenerated, 1
glyceraldehyde 3-phosphate created
uses enzymes that functions best under light
glyceraldehydes 3-phosphate - 3-carbon sugar that can be
converted to fructose 6-phosphate and glucose 1-phosphate in
cytoplasm w/ reversed glycolysis reactions
glucose 1-phosphates combined into insoluble polymer as starch when
there’s high levels of glyceraldehydes 3-phosphate
energy cycle - metabolisms of chloroplasts/mitochondria are related
photosynthesis uses products of respiration as starting substrates
respiration uses products of photosynthesis as starting substrates
Calvin cycle uses part of glycolytic pathway, in reverse, to make
enzymes used in both processes similar or the same
photorespiration - releases CO2 by attaching O2 to RuBP, reversing
Calvin cycle
rubisco can oxidize RuBP, undoing the Calvin cycle
CO2/O2 compete for same active site on rubisco enzyme
at 25°C, rate of carboxylation 4x that of oxidation (20% of fixed
carbon lost)
higher temperature >> stomata close to conserve H2O >> CO2 can’t
go in >> favors photorespiration
25-50% of photosynthetically fixed carbon lost through
C4 photosynthesis - phosphoenolpyruvate (PEP) carboxylated to
make 4-carbon compound
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