Calvin Cycle *_*

3 steps of Calvin Cycle

1. fixation

2. reduction

3. regeneration of acceptor

Ru1,5bP

ribulose 1,5-bisphosphate

triose phosphate

glyceraldehyde 3-phosphate

where does the Calvin Cycle take place?

chloroplast stroma

electrophile for Rubisco-catalyzed reaction

CO2

what catalytic strategies does Rubisco use?

proximity, alignment of electrophile and nucleophile using Mg2+ ion

Rubisco

catalyzes covalent attachment of CO2 to ribulose 1,5-bisphosphate and then cleavage of unstable 6C intermediate to form 2x 3-phosphoglycerates

does rubisco prefer CO2 or O2 at high temperatures?

O2

photorespiration

occurs when rubisco mistakenly adds O2 instead of CO2 to Ru-5-P

step 2 of the Calvin cycle

conversion of 3-phosphoglycerate to glyceraldehyde 3-phosphate

what conditions allow for the thermodynamically unfavorable formation of glyceraldehyde 3-phosphate in step 2 of the Calvin Cycle?

high concentrations of NADPH and ATP

what enzyme catalyzes the carbon fixing reaction?

rubisco

substrates of rubisco

ribulose 1,5-bisphosphate and CO2

products of rubisco-catalyzed reaction

2 3-phosphoglycerate molecules

dark reactions

CO2 assimilation; production of ATP and NADPH by photophosphorylation and the incorporation of CO2 into trios phosphate

net product of photosynthesis

1 molecule of glyceraldehyde 3-phosphate

net result of 2 turns of CO2 assimilation in Calvin Cycle

3 CO2 + Phosphate —> 1 triose phosphate

how much NADPH and ATP is required for the formation of one triose phosphate?

6 NADPH and 9ATP

what produces the NADPH and ATP needed for the formation of triose phosphate in the dark reactions/CO2 assimilation?

light-dependent reactions of photosynthesis

what happens to the 5 triose phosphates that are not released as product?

rearranged to form 3x ribulose 1,5-bisphosphate

all enzymes of the Calvin Cycle operate near equilibrium except which 2?

kinase and phosphatase

name the enzymes that catalyze the 3 irreversible/exergonic reactions of stage 3 of the Calvin Cycle

1. fructose 1,6-bisphosphate

2. sedoheptulose 1,7-bisphosphatase

3. ribulose 5-phosphate kinase

stage 3 of the Calvin Cycle

regeneration of ribulose 1,5-bisphosphate and interconversion of triose phosphates with PPP intermediates

sedoheptulose 7-phosphate

transaldolase

catalyzes transfer of top 3 carbons to a different aldose; mechanism = aldol cleavage then aldol condensation to different bottom

transketolase

catalyzes transfer of top 2 carbons to different aldose; mechanism requires TPP cofactor

products of pentose phosphate pathway

NADPH and ribose (leads to RNA and DNA)

predominant pathway of catabolism in RBC

pentose phosphate pathway

TPP

important cofactor; allows cleavage of a C-C bond adjacent to carbonyl

erythrose

ribose

ribulose

which pathway begins with oxidative steps?

Calvin Cycle

Pentose phosphate pathway

Both

pentose phosphate pathway

which pathway can produce ribose for RNA and DNA synthesis?

Calvin Cycle

Pentose phosphate pathway

Both

both

which pathway occurs in the chloroplast?

Calvin Cycle

Pentose phosphate pathway

Both

Calvin cycle

which pathway involves a transketolase?

Calvin Cycle

Pentose phosphate pathway

Both

both

which pathway yields NADPH for anabolic reactions in the cell?

pentose phosphate

aldolase

splits a ketose into a smaller ketose plus an aldose