Photosynthesis AP Biology Photosynthesis Life from Light and

Photosynthesis AP Biology

Photosynthesis: Life from Light and Air

Autotrophs; self-feeders…plants, protists, algae, bacteria Photoautotrophs; use light energy to synthesize organic compounds Chemoautotrophs; use energy from inorganic compounds (hydrogen sulfide, ammonia) to synthesize organic compounds Producers produce organic compounds Heterotrophs; other-feeders Consumers consume organic compounds

Energy needs of life Heterotrophs consumers animals fungi most bacteria Autotrophs producers plants photosynthetic bacteria (blue-green algae)

How are they connected? Heterotrophs making energy & organic molecules from ingesting organic molecules glucose + oxygen carbon + water + energy dioxide C 6 H 12 O 6 + 6 O 2 6 CO 2 + 6 H 2 O + ATP exergonic Autotrophs making energy & organic molecules from light energy carbon + water + energy glucose + oxygen dioxide 6 CO 2 + 6 H 2 O +light energy endergonic C 6 H 12 O 6 + 6 O 2

Energy cycle sun Photosynthesis plants CO 2 glucose H 2 O animals, plants Cellular Respiration ATP O 2

What does it mean to be a plant Need to… collect light energy transform it into chemical energy ATP store light energy in a stable form to be moved around glucose the plant & also saved for a rainy day need to get building block atoms from the environment CO 2 H 2 O C, H, O, N, P, K, S, Mg produce all organic molecules N needed for growth K P … carbohydrates, proteins, lipids, nucleic acids

Plant structure Obtaining raw materials sunlight leaves = solar collectors CO 2 stomates = gas exchange H 2 O uptake from roots nutrients N, P, K, S, Mg, Fe… uptake from roots

stomate transpiration

Chloroplasts Leaf absorb sunlight & CO 2 Chloroplasts contain Chlorophyll make energy & sugar

Plant structure Chloroplasts double membrane stroma fluid-filled interior thylakoid sacs grana stacks Thylakoid contains membrane chlorophyll molecules electron transport chain ATP synthase H+ gradient built up within thylakoid sac + H+ + + H H+ H+ H+ HH+ +H H

Photosynthesis Light reactions light-dependent energy production reactions convert ATP reactions solar energy to chemical energy & NADPH Calvin cycle light-independent sugar reactions production reactions uses chemical energy (ATP & NADPH) to reduce CO 2 & synthesize C 6 H 12 O 6

Light Reactions H 2 O + light energy H 2 O + NADPH + O 2 § produces ATP § produces NADPH § releases O 2 as a waste product sunlight Energy Building Reactions NADPH ATP O 2 ATP

Calvin Cycle CO 2 + ATP + NADPH C 6 H 12 O 6 CO 2 ADP NADP Sugar Building Reactions NADPH ATP sugars C 6 H 12 O 6 + ADP + NADP § builds sugars § uses ATP & NADPH § recycles ADP & NADP back to make more ATP & NADPH

Putting it all together CO 2 light + H 2 O + energy H 2 O CO 2 sunlight ADP Energy Building Reactions NADP Sugar Building Reactions NADPH ATP O 2 sugars C 6 H 12 O 6 + O 2 Plants make both: § energy §ATP & NADPH § sugars

Light reactions Electron Transport Chain like in cellular respiration membrane-bound proteins in organelle electron acceptors NADPH proton (H+) gradient across inner membrane Where’s the double membrane? ATP synthase enzyme + +H+ H H+ +H+ H+H + H H + +H+ H+ H+H + + H+ H H

The ATP that Jack built photosynthesis sunlight respiration breakdown of C 6 H 12 O 6 H+ moves the electrons runs the pumps the protons forms the gradient drives the flow of protons ADP + Pi through ATP synthase § attaches Pi to ADP ATP § forms the ATP … that evolution built § § § H+ H+

ETC of Respiration § Mitochondria transfer chemical energy from food molecules into chemical energy of ATP use electron carrier NADH generate H 2 O

ETC of Photosynthesis § Chloroplasts transform light energy into chemical energy of ATP use electron carrier NADPH

Pigments of photosynthesis Why does this molecular structure make sense? Chlorophyll & other pigments embedded in thylakoid membrane arranged in a “photosystem” structure-function relationship

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A Look at Light The spectrum of color V I B G Y O R

Light: absorption spectra Photosynthesis gets energy by absorbing wavelengths of light chlorophyll absorbs other a best in red & blue wavelengths & least in green pigments with different structures absorb light of different wavelengths

Photosystems of photosynthesis 2 photosystems in thylakoid membrane collections act of chlorophyll molecules as light-gathering “antenna complex” Photosystem chlorophyll II a reaction center P 680 = absorbs 680 nm wavelength red light Photosystem chlorophyll I b P 700 = absorbs 700 nm wavelength red light antenna pigments

ETC of Photosynthesis Photosystem II Photosystem I

ETC of Photosynthesis 3 1 H+ 4 H+ H+ H+ ADP + Pi ATP H+ to the Calvin Cycle

ETC of Photosynthesis 3 2 1 H+ 4 H+ H+ H+ ADP + Pi ATP H+ to the Calvin Cycle

ETC of Photosynthesis electron carrier 6 5 $$ in the bank… reducing power to the Calvin Cycle

ETC of Photosynthesis split H 2 O

ETC of Photosynthesis ETC produces from light energy ATP & NADPH go PS to Calvin cycle II absorbs light excited electron passes from chlorophyll to “primary electron acceptor” need to replace electron in chlorophyll enzyme extracts electrons from H 2 O & supplies them to chlorophyll splits H 2 O O combines with another O to form O 2 released to atmosphere and we breathe easier!

Experimental evidence Where did the O 2 come from? radioactive tracer = O 18 Experiment 1 6 CO 2 + 6 H 2 O +light energy C 6 H 12 O 6 + 6 O 2 Experiment 2 6 CO 2 + 6 H 2 O +light energy Proved O 2 came from H 2 O not CO 2 = plants split H 2 O

Noncyclic Photophosphorylation Light reactions elevate electrons in 2 steps (PS II & PS I) PS II generates energy as ATP PS I generates reducing power as NADPH

Cyclic photophosphorylation If PS I can’t pass electron to NADP… it cycles back to PS II & makes more ATP, but no NADPH coordinates light reactions to Calvin cycle uses more ATP than NADPH X

Photophosphorylation cyclic photophosphorylation noncyclic photophosphorylation

Photosynthesis summary Where did the energy come from? Where did the electrons come from? Where did the H 2 O come from? Where did the O 2 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? …stay tuned for the Calvin cycle

Photosynthesis animations: Biology; Medicine Animations Pearson Marketing Modeling the reactions

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

How is that helpful? Want to make C 6 H 12 O 6 synthesis How? From what? What raw materials are available? CO 2 carbon fixation NADPH NADP C 6 H 12 O 6 reduce CO 2 NADP

From CO 2 C 6 H 12 O 6 CO 2 has very little chemical energy fully oxidized C 6 H 12 O 6 contains a lot of chemical energy reduced endergonic Reduction of CO 2 C 6 H 12 O 6 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

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

Remember G 3 P? glucose C-C-C-C 2 ATP 2 ADP glycolysis fructose-6 P P-C-C-C-P DHAP G 3 P P-C-C-C-P pyruvate C-C-C 2 2 4 4 NAD+ NADH ADP ATP

Calvin Cycle Stroma of chloroplast Carbon dioxide (CO 2) Rubisco Ribulose 1, 5 -bisphosphate (Ru. BP) (5 C) 3 -phosphoglycerate (3 C) (PGA) Carbon fixation 3 ADP Reforming Ru. BP 3 ATP 2 Pi 6 ATP 6 ADP 1, 3 -bisphoglycerate (3 C) 6 NADPH Reverse of glycolysis 6 NADP+ 6 Pi Glyceraldehyde 3 -phosphate (3 C) (G 3 P) Glucose and other sugars

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

Rubisco Enzyme which fixes carbon from air ribulose the bisphosphate carboxylase 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 G 3 P 3 CO 2 1 G 3 P (3 C) 6 turns of Calvin cycle = 1 C 6 H 12 O 6 (6 C) 6 CO 2 1 C 6 H 12 O 6 (6 C) 18 ATP + 12 NADPH 1 C 6 H 12 O 6 any ATP left over from light reactions will be used elsewhere by the cell

Photosynthesis summary Light reactions produced ATP produced NADPH consumed H 2 O produced O 2 as byproduct Calvin cycle consumed CO 2 produced G 3 P (sugar) regenerated ADP regenerated NADP NADP

In hot, dry environments you don’t want to dessicate. Plants close their stomata to avoid transpiration, but carbon dioxide levels begin to drop… The Calvin Cycle will begin to use oxygen instead of carbon dioxide in a process called photorespiration. Alternative strategies are needed…

C 4 Photosynthesis Makes a 4 -carbon intermediate organic compound (even at low carbon dioxide concentrations) that is sent to the bundle-sheath cells. This keeps the carbon concentration high in these cells and the Calvin Cycle can proceed as normal. Ex. Sugar cane, corn CAM Crassulacean acid metabolism Organic acids made at night to store carbon, then carbon dioxide is released the next morning when ATP and NADPH are available for the Calvin Cycle. Ex. Pineapple, cacti, other succulents (water-storers)

One separates the first steps of carbon fixation steps in space (C 4) and the other separates them in time (CAM), but in each process carbon dioxide is eventually sent into the Calvin Cycle.

Summary of photosynthesis 6 CO 2 + 6 H 2 O +light energy C 6 H 12 O 6 + 6 O 2 Where did the CO 2 come from? Where did the CO 2 go? Where did the H 2 O come from? Where did the H 2 O go? Where did the energy come from? What’s the energy used for? What will the C 6 H 12 O 6 be used for? Where did the O 2 come from? Where will the O 2 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 air Then all the cats, dogs, rats, people & elephants… are really strands of air woven together by sunlight! sun