Calvin Cycle: Life from Air photosynthesis Calvin Cycle: Life from Air

Whoops! Wrong Calvin… The Calvin Cycle

Remember what it means to be a plant Need to produce all organic molecules necessary for life Carbohydrates, lipids, proteins, nucleic acids Need to store chemical energy (ATP) produced from light reactions In a more stable form That can be moved around the plant Than can be saved for a rainy day + water + energy  glucose + oxygen carbon dioxide 6CO2 6H2O C6H12O6 6O2 light energy  +

photosynthesis Light reactions ATP Convert solar energy to chemical energy ATP  energy NADPH  reducing power What now? Build stuff!! ATP photosynthesis

How is that helpful? CO2 ATP Want to make C6H12O6 How? From what? What raw materials are available?? ATP CO2

From Co2  c6h12o6 CO2 C6H12O6 CO2 has very little chemical energy Fully oxidized C6H12O6 contains a lot of chemical energy Highly reduced Synthesis = endergonic process Put in a lot of energy Reduction of CO2  C6H12O6 proceeds in many small uphill steps Each catalyzed by a specific enzyme Uses the energy stored in ATP & NADPH CO2 NADPH NADP C6H12O6 carbon fixation

From light reactions to calvin cycle Occurs in the stroma Need products of light reactions to drive synthesis reactions ATP NADPH ATP

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

Calvin cycle

G3P glycolysis glucose G3P Photosynthesis We’ve seen G3P before? C-C-C-C-C-C fructose-1,6bP P-C-C-C-C-C-C-P DHAP P-C-C-C G3P C-C-C-P pyruvate C-C-C ATP 2 ADP 4 NAD+ glyceraldehyde 3-phosphate G3P We’ve seen G3P before? Do you remember where? glycolysis Photosynthesis

To g3p & beyond Glyceraldehyde-3-P G3P is an important intermediate End product of Calvin cycle Energy rich 3-carbon sugar “C3 photosynthesis” G3P is an important intermediate G3P  glucose  carbohydrates G3P  lipids  phospholipids, fats, waxes G3P  amino acids  proteins G3P  nucleic acids  DNA, RNA

rubisco Enzyme responsible for carbon fixation Ribulose bisphosphate carboxylase RuBisCo The most important enzyme in the world! It makes life out of AIR! Definitely the most abundant enzyme I’m green with envy! It’s not easy being green!

accounting The accounting is complicated 3 turns of Calvin cycle = 6G3P 3 CO2 = 6G3P 6 turns of Calvin cycle = 1 C6H12O6 6 CO2 = 1 C6H12O6 18 ATP + 12 NADPH  1 C6H12O6 Any leftover ATP from light reactions will be used elsewhere by the cell Growth, reproduction, movement, etc

accounting The accounting is complicated Now we need to generate RuBP 5 G3P = 3 RuBP 3 CO2  6 G3P  3 RuBP + ½ C6H12O6

Photosynthesis summary Light reactions Produced ATP Produced NADPH Consumed H2O Produced O2 as a byproduct Calvin cycle Consumed CO2 Produced G3P (sugar) Regenerated ADP Regenerated NADP ADP NADP

Light reactions  H2O O2 light energy + Produced ATP Produced NADPH sunlight Produced ATP Produced NADPH Consumed H2O Produced O2 as a byproduct Energy Building Reactions NADPH ATP O2

Calvin cycle  CO2 + Consumed CO2 Produced sugar Used ATP & NADPH C6H12O6  + NADP ATP NADPH ADP Consumed CO2 Produced sugar Used ATP & NADPH Regenerated ADP &NADP CO2 ADP NADP Sugar Building Reactions NADPH ATP sugars

Putting it all together CO2 H2O C6H12O6 O2 light energy  + H2O CO2 Plants make energy ATP & NADPH Plants store energy as sugar sunlight ADP NADP Energy Building Reactions Sugar Building Reactions NADPH ATP O2 sugars

Energy cycle ATP Photosynthesis Cellular Respiration sun CO2 O2 H2O even though this equation is a bit of a lie… it makes a better story sun Energy cycle Photosynthesis CO2 H2O C6H12O6 O2 light energy  + H2O plants CO2 glucose O2 animals, plants CO2 H2O C6H12O6 O2 ATP energy  + Cellular Respiration ATP The Great Circle of Life!

Photosynthesis summary 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 did the O2 go? What is missing from this equation?

Supporting the biosphere On a global scale, photosynthesis is the most important process for the continuation of life on Earth each year photosynthesis … Captures 121 billion tons of CO2 Synthesizes 160 billion tons of carbohydrates Heterotrophs are dependent on plants as a food source for fuel & raw materials

If plants can do it, then you can learn it. Any questions?