Photosynthesis: The Calvin Cycle Life from Air 2006-2007

Whoops! Wrong Calvin… The Calvin Cycle

Remember what it means to be a plant… Need to produce all organic molecules necessary for growth carbohydrates, lipids, proteins, nucleic acids Need to store chemical energy (ATP) produced from light reactions in stable form can be moved around plant saved for a rainy day

+ water + energy  glucose + oxygen Autotrophs Making energy & organic molecules from light energy photosynthesis + water + energy  glucose + oxygen carbon dioxide 6CO2 6H2O C6H12O6 6O2 light energy  + So, in effect, photosynthesis is respiration run backwards powered by light.

  build stuff !! Light reactions Convert solar energy to chemical energy ATP NADPH What can we do now?  energy  reducing power   build stuff !!

CO2 C6H12O6 How is that helpful? Want to make C6H12O6 synthesis How? From what? What raw materials are available? CO2 CO2 contains little energy because it is fully oxidized Reduce CO2 in a series of steps to synthesize a stable energy storage molecule NADPH reduce CO2 carbon fixation NADP NADP C6H12O6

From CO2  C6H12O6 CO2 has very little chemical energy fully oxidized C6H12O6 contains a lot of chemical energy reduced endergonic Reduction of CO2  C6H12O6 proceeds in many small uphill steps each catalyzed by specific enzyme using energy stored in ATP & NADPH

From Light reactions to Calvin cycle chloroplast stroma Need products of light reactions to drive synthesis reactions ATP NADPH

Calvin cycle 1C 5C 6C 3C 3C 3C CO2 RuBP Rubisco 3 ATP 3 ADP used 1. Carbon fixation C 3. Regeneration of RuBP C 5C C RuBP Rubisco C ribulose bisphosphate 6C starch, sucrose, cellulose & more ribulose bisphosphate carboxylase C 3 ADP 3 ATP C used to make glucose C glyceraldehyde-3-P C RuBP = ribulose bisphosphate Rubisco = ribulose bisphosphate carboxylase 3C G3P PGA C phosphoglycerate C 3C C C C = C C C 6 ADP 6 ATP 2. Reduction C | H C – C 6 NADP 6 NADPH 3C C

Remember G3P? glycolysis glucose fructose-6P DHAP G3P pyruvate 2 ATP C-C-C-C-C-C Remember G3P? 2 ATP glycolysis 2 ADP fructose-6P P-C-C-C-C-C-C-P DHAP P-C-C-C G3P C-C-C-P 2 NAD+ 2 NADH Gluconeogenesis == making new glucose 4 ADP 4 ATP pyruvate C-C-C

Calvin Cycle Stroma of chloroplast Carbon dioxide (CO2) Rubisco Ribulose 1,5-bisphosphate (RuBP) (5C) 3-phosphoglycerate (3C) (PGA) 6 ATP Carbon fixation 3 ADP 6 ADP Reforming RuBP 1,3-bisphosphoglycerate (3C) 3 ATP 6 NADPH 2Pi Reverse of glycolysis 6 NADP+ 6Pi Glyceraldehyde 3-phosphate (3C) Glyceraldehyde 3-phosphate (3C) (G3P) Glyceraldehyde 3-phosphate (3C) (G3P) Glucose and other sugars

To G-3-P and Beyond! Glyceraldehyde-3-P G-3-P = important intermediate end product of Calvin cycle energy rich 3 carbon sugar “C3 photosynthesis” G-3-P = important intermediate G-3-P   glucose   carbohydrates   lipids   amino acids   nucleic acids

Rubisco Enzyme which fixes carbon from air ribulose bisphosphate carboxylase the most important enzyme in the world! it makes life out of air! definitely the most abundant enzyme

Accounting The accounting is complicated 3 turns of Calvin cycle = 1 G3P 3 CO2 1 G3P (3C) 6 turns of Calvin cycle = 1 C6H12O6 (6C) 6 CO2 1 C6H12O6 (6C) 18 ATP + 12 NADPH  1 C6H12O6 any ATP left over from light reactions will be used elsewhere by the cell

Photosynthesis summary Light reactions produced ATP produced NADPH consumed H2O produced O2 as byproduct Calvin cycle consumed CO2 produced G3P (sugar) regenerated ADP regenerated NADP ADP NADP

Summary of photosynthesis 6CO2 6H2O C6H12O6 6O2 light energy  + Where did the CO2 come from? Where did the CO2 go? Where did the H2O come from? Where did the H2O go? Where did the energy come from? What’s the energy used for? What will the C6H12O6 be used for? Where did the O2 come from? Where will the O2 go? What else is involved…not listed in this equation?

Supporting a biosphere On global scale, photosynthesis is the most important process for the continuation of life on Earth each year photosynthesis synthesizes 160 billion tons of carbohydrate heterotrophs are dependent on plants as food source for fuel & raw materials

The poetic perspective… All the solid material of every plant was built by sunlight out of thin air All the solid material of every animal was built from plant material sun air Then all the cats, dogs, rats, people & elephants… are really strands of air woven together by sunlight!

Any Questions?? 2006-2007