Calvin Cycle Melvin Calvin – used C-14 as a tracer to discover the how the cycle works

Calvin Cycle 3 steps Carbon dioxide fixation Carbon dioxide reduction Regeneration of RuBP(ribulose bisphosphate)

Carbon Dioxide Fixation Carbon dioxide from atmosphere attaches to RuBP, a 5 carbon molecule = 6 carbon molecule Splits into 2 3C molecules called 3PG (phosphoglycerate) RuBP carboxylase is enzyme in this reaction

Carbon Dioxide Reduction 2 3PG (phosphoglycerate) undergoes reduction to G3P in 2 steps 3PG  BPG  G3P Uses some ATP and NADPH from light reactions

Regeneration of RuBP Takes 3 turns of cycle to allow 1 G3P to exit. For every 3 turns, 5 molecules of G3P are used to re-form 3 molecules of RuBP 5 G3P + ATP(from light reactions) 3 RuBP

Importance of Calvin Cycle G3P is the product of the Calvin cycle G3P can be converted to many organic molecules Metabolism of G3P can result in Glucose phosphate Can use to metabolize energy needed Combine with fructose to produce sucrose, used in transport in plants Starting point for starch and cellulose Hydrocarbon skeleton can be used to make fatty acids and glycerol Nitrogen and hydrocarbon skeleton can make AA’s

Other types of photosynthesis C3 plants – most green plants (azaleas, maples) Use RuBP carboxylase to fix carbon Photorespiration – when oxygen levels are high, carbon dioxide levels are low, oxygen combines with RuBP and only 1 molecule of 3PG is made and Carbon dioxide is released.

C4 photosynthesis (corn, crabgrass…) Arranged differently than C3 plants Mesophyll cells surround the bundle sheath cells Bundle sheath cells and mesophyll cells have chloroplasts Use PEP carboxylase to fix carbon dioxide  PEP, to form oxaloacetate ( a 4 carbon molecule) within mesophyll cells which is pumped into the bundle sheath cells, where Carbon dioxide enters the Calvin cycle

C4 plants have an advantage over C3 plants in the hot, dry climates because they do not enter photorespiration. Think about it!!

CAM photosynthesis CAM – Carassulaceae acid metabolism Family of succulent plants (includes cacti) At night, plants use PEPCase to fix some CO2 forming C4 molecules During day, C4 molecules release CO2 to the Calvin cycle…