Photosynthesis Photosynthesis with Hank! Life from Light and Air

Obtaining the materials sunlight leaves = solar collectors CO2 stomates = gas exchange H2O uptake from roots nutrients N, P, K, S, Mg, Fe…

Concurrent Reactions

Light-Dependent Reactions *Key to these rxns is light absorption Success lies in photosystems – 2 part complex Antenna complex – site of absorption; excites electrons & passes them on Reaction center – redox-rxns occur here; excited ele- transferred to electron acceptor

reaction center antenna pigments

To Calvin Cycle!!! Stroma ATP! NADPH ADP + P NADP + + 2H + PS 700 PS 680 H+ + ½ O2 + Lumen - NADP+ Reductase - Cytochrome complex - ferredoxin - pheophytin - ATP Synthase - ele - - plastoquinone - H + ion

Step 1: Light absorbed in PS II excites ele- (from H2O splitting) → passed to electron acceptor (pheophytin) Step 2: Plastoquinone(PQ) shuttles high energy ele- through series of redox rxns (ETC 1); passes through cytochrome complex, driving in H+, ↑ [H+] = ↓ pH Step 3: De-energized ele- are passed off to plastocyanin (PC) → PS I re-excites ele- and ferredoxin shuttles through ETC 2 Step 4: a) Ele- reduce NADP+ to NADPH at NADP+ reductase b) H+ pumped out via ATP Synthase – activates chemiosmosis → production of ATP from ADP

Regulation of the Light Reaction Calvin cycle uses more ATP than NADPH If there is enough, NADPH production is turned off ATP 18 ATP + 12 NADPH  1 C6H12O6

Review Animations Light dependent reactions

Light-INdependent Reactions Want to make C6H12O6 → synthesis **How? From what? What raw materials are available? CO2 NADPH reduces CO2 carbon fixation NADP NADP C6H12O6

From CO2  C6H12O6 CO2 has very little chemical energy fully oxidized C6H12O6 has 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 specific enzyme uses energy stored in ATP & NADPH ←from light rxns!

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 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 C PGA G3P aka PGAL 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! Resulting 3-C Sugar G3P  glucose  carbohydrates - important intermediate G3P  glucose  carbohydrates  lipids  phospholipids, fats, waxes  amino acids  proteins  nucleic acids  DNA, RNA

A little more about RuBisCo… Enzyme which fixes carbon from air ribulose bisphosphate carboxylase the most important enzyme in the world! **It makes life out of air!** most abundant enzyme

“Banking” Keeping the books straight… 6 turns of Calvin cycle = 1 C6H12O6 (6C) 6 CO2  1 C6H12O6 (6C) 18 ATP + 12 NADPH  1 C6H12O6 Left over ATP from light reactions used elsewhere by cell

Sum it Up: Light Reactions H2O ATP O2 light energy  + NADPH H2O sunlight produces ATP & NADPH releases O2 as waste 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+ ADP NADP Sugar Building Reactions NADPH ATP sugars

Supporting a biosphere Big Picture: photosynthesis is THE most important process for continuation of life on Earth Each year photosynthesis… captures 121 billion tons of CO2 synthesizes 160 billion tons of carbohydrates heterotrophs depend on plants for food, fuel, & raw materials

Light Depedent Review: Where did the energy come from? Where did the electrons come from? Where did the H2O come from? Where did the O2 come from? Where did the O2 go? Where did the H+ come from? Where did the ATP come from? What will the ATP be used for? Where did the NADPH come from? What will the NADPH be used for?

Light Independent Review II: 6CO2 6H2O C6H12O6 light energy  + 6O2 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?

Adaptations in Alternative Environments C4 Path CO2 stored is mesophyll & released in vascular tissue

Adaptations in Alternative Environments CAM Path Stomata open at night – CO2 stored in vacuoles for later use

Combating Photorespiration Photorespiration – rxn between RuBP & O2 when [O2] is high → uses ATP & produces CO2 Favored ONLY when [O2] exceeds [CO2] Store CO2 C4 Path CAM Plants