Photosynthesis part deux:The Calvin Cycle
Chapter 6-2 pages 117-120
At right is Melvin Calvinwho worked all this out
Below is Calvin whoworked out Calvin Ball
Calvin Cycle
•Fromphotosynthesis weget ATP andNADPH
•Now we’ll use theenergy from that tomake biomolecules
•The energy from Niagra falls isused to power turbines so we canuse electricity to do work
Carbon Fixation
•Carbon fixation is thebuilding of biomoleculesfrom CO2
•3 steps of the CalvinCycle
1. CO2 diffuses into the stromafrom the surroundingcytoplasm. RuBP iscombined with CO2. Thenew 6 Carbon moleculesplits into 2 3 Carbonmolecules called PGA
Calvin Cycle
Step 2
2 PGAs converted to another 3 Carbon molecule PGAL,
in a two part process
1. PGA receives a Phosphate from ATP
2. NADPH gives its H+
The ADP, NADP+, and Phosphate are reused back in the photosynthesis reaction
•Confused, stare at thispicture, watch the linesseem to move. Now getback to work
Calvin Cycle
Step 3
Some of the PGALgoes back to RuBPso the Cycle cancontinue
Other PGAL goeselsewhere to makeBiomolecules
Balance sheet for Photosynthesis
•Calvin Cycle has toturn 3 times to get aPGAL
–That uses 9 ATPs and6 NADPHs
•Now no glucose hasbeen made yet.Cellular respiration iswhere Glucose isinvolved.
The Lakers appreciatethe Calvin Cycle, youshould to.
Alternative pathways
•C3 Plants only fix carbonthrough the Calvin Cycle
–Most plants are this, treesfor example
•In hot climates plants losewater through openstomata so they need tokeep stomata closed
•But stomata are whereCO2 & O2 leave and enterthe cell
Alternative Pathways
•C4 pathway plants putCO2 into 4 carbonmolecules
–Corn & Sugar Cane areexamples
•CAM pathway plantshave stomata open atnight and closedduring the day, theopposite as normal
–includes Cactus &Pineapple
