Transcript The Calvin Cycle - Downey Unified School District

The Calvin
Cycle
Named after Melvin Calvin (1911-1997)
• The Calvin Cycle
Carbon atoms from CO2 are
bonded or “fixed” into organic
molecules
Carbon Fixation – the
incorporation of CO2 into organic
molecules
Step#1 of 3 in the Calvin cycle
CO2 enters through the stoma, diffuses into
cytosol then it enters the stroma of the
chloroplast.
Enzyme combines CO2 with a five carbon
compound RuBP
This produces a six carbon compound
This Splits into a pair of three carbon
compounds PGA
Step #2 –
PGA is converted into another threecarbon molecule called PGAL.
PGA receives a phosphate from ATP
then the resulting compound receives a
proton from NADPH this causes the
received phosphate to be released
producing PGAL
The ending products are NADP+ and
ADP
Step #3
PGAL is converted back into RuBP
This step requires ATP which is
changed to ADP
This step allows the Calvin cycle to
continue
Some PGAL Molecules are not
converted into RuBP but they leave the
cycle and make organic compounds
C3 Pathway
 All Plants that fix carbon using the Calvin
Cycle are C3 Plants
 Low CO2 or high O2 will slow the Calvin
Cycle
 When the Stoma is closed there will be less
CO2
 When Photosynthesis is running it makes O2
C4 Pathway
 Fixes a four carbon molecule
 Corn, Sugar cane and Crabgrass
(monocots)
CAM Pathway
 Stands for Crassulacean Acid Metabolism
 Plants that live in arid environments
 Cactuses, and pineapple