Photosynthesis: The Calvin Cycle Life from Air 2007-2008

From CO2  C6H12O6 CO2 has very little chemical energy fully oxidized C6H12O6 contains a lot of chemical energy Synthesis = endergonic process Reduction of CO2  C6H12O6 proceeds in many small uphill steps each catalyzed by a 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 stroma ATP thylakoid

Calvin cycle 1C 5C 6C 5C 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 3 ADP 3 ATP C ribulose bisphosphate carboxylase 5C C used to make glucose C glyceraldehyde-3-P C 1. A five-carbon sugar molecule called ribulose bisphosphate, or RuBP, is the acceptor that binds CO2 dissolved in the stroma. This process, called CO2 fixation, is catalyzed by the enzyme RuBP carboxylase, forming an unstable six-carbon molecule. This molecule quickly breaks down to give two molecules of the three-carbon 3-phosphoglycerate (3PG), also called phosphoglyceric acid (PGA). 2. The two 3PG molecules are converted into glyceraldehyde 3-phosphate (G3P, a.k.a. phosphoglyceraldehyde, PGAL) molecules, a three-carbon sugar phosphate, by adding a high-energy phosphate group from ATP, then breaking the phosphate bond and adding hydrogen from NADH + H+. 3. Three turns of the cycle, using three molecules of CO2, produces six molecules of G3P. However, only one of the six molecules exits the cycle as an output, while the remaining five enter a complex process that regenerates more RuBP to continue the cycle. Two molecules of G3P, produced by a total of six turns of the cycle, combine to form one molecule of glucose. 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

To G3P and 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   lipids   phospholipids, fats, waxes   amino acids   proteins   nucleic acids   DNA, RNA

It’s not easy being green! 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 It’s not easy being green! I’m green with envy!

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

Light Reactions  produces ATP produces NADPH H2O ATP O2 light energy  + NADPH H2O sunlight produces ATP produces NADPH releases O2 as a waste product Energy Building Reactions NADPH ATP O2

Calvin Cycle  builds sugars uses ATP & NADPH recycles ADP & NADP CO2 C6H12O6  + NADP ATP NADPH ADP CO2 builds sugars uses ATP & NADPH recycles ADP & NADP back to make more ATP & NADPH ADP NADP Sugar Building Reactions NADPH ATP sugars

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? Where did the CO2 come from? air Where did the CO2 go? carbohydrate (G3P) Where did the H2O come from? soil (xylem) Where did the H2O go? split to donate e- & H+ Where did the energy come from? sun What’s the energy used for? to make ATP in light reactions What will the C6H12O6 be used for? the work of plant life Where did the O2 come from? splitting of H2O Where will the O2 go? air or respiration What else is involved…not listed in this equation? ATP, ADP, NADP, NADPH

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 plants, cats, dogs, elephants & people … are really particles of air woven together by strands of sunlight!

If plants can do it… You can learn it! Ask Questions!! 2007-2008