Exam 1: Ch 20 Carbon Assimilation Flashcards
overall rxn
CO2 + H2O –> C6H12O6 + O2
CO2 + H2O –> HCO3- + H+
gluconeogenesis
glucose can be made by any intermediate in glycolysis/gluconeogenesis
plants intersect gluconeogenesis at 3-P-G
CO2 is fixed and converted to…
3-phosphoglycerate
is carbon assimilation energy intensive?
yes, uses 9 ATP and 6 NADPH per 3-P-G
how many stages in calvin cycle
3
stage 1 of calvin
(3 )CO2 fixed to (3 )ribulose 1,5 bisphosphate
(3) ribulose 1,5 bisphosphate turned into (6) 3-P-G
stage 2 of calvin
(6) 3-P-G reduced to (6) glyceraldehyde-3-P
stage 3 of calvin
(5) glyceraldehyde-3-P used to regenerate (3) ribulose 1,5 bisphosphate
(1) G-3-P sent to gluconeogenesis
CO2 (step 1) is fixed by which enzyme?
rubisco
rubisco
multisubunit (main unit encoded by chloroplast DNA)
Kcat = 3/sec
plants make tons of rubisco b/c low Kcat
step 2 enzyme
uses glycolytic enzymes except for G-3-P dehydrogenase
chloroplast has isozyme w/ preference for NADPH
requires ATP and NADPH to make G-3-P
which step uses the pentose phosphate pathway
step 3
regeneration of ribulose 1,5 bisP from G-3-P
what does the PPP do normally
convert 5 glucose (6 carbon molecule) to 6 riboses (5 carbon molecules)
transfers either 2C or 3C units
uses 3C, 4C, 7C sugars
uses 2 turns of the enzyme
why do we have the PPP
can’t transfer 1C units easily due to instability (likely to leave as CO2)
enzymes of PPP
transaldolase: 3C transfer
transketolase: 2C transfer
