AP Biology 2007 2008 Photosynthesis Life from Light

AP Biology 2007 -2008

Photosynthesis: Life from Light and Air AP Biology

PHOTOSYNTHESIS CO 2 + 2 H 2 O (CH 2 O) + H 2 O + O 2 Carbon dioxide + water carbohydrate + water + oxygen 6 times 6 CO 2 + 6 H 2 O C 6 H 12 O 6 + 6 O 2 Carbon dioxide + water GLUCOSE + oxygen AP Biology

REDOX REACTION § Photosynthesis is an oxidation- § § reduction reaction Oxidation = loss of electrons Reduction = gain of electrons u AP Biology Electrons travel with a Hydrogen Ion (H+ + e-)

chloroplast Plant structure H+ ATP + + H+ H H+ + H H + H+ H+ H+ + H H thylakoid § Chloroplasts u u double membrane stroma outer membrane inner membrane § fluid-filled interior u u thylakoid sacs grana stacks stroma § Thylakoid membrane contains u u u chlorophyll molecules electron transport chain ATP synthase § H+ gradient built up within AP Biology thylakoid sac thylakoid granum

Photosynthesis AP Biology

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

thylakoid chloroplast Light reactions § Electron Transport Chain § like in cellular respiration proteins in organelle membrane u electron acceptors u § NADPH u proton (H+) gradient across inner membrane § find the double membrane! u ATP synthase enzyme AP Biology + +H+ H H+ + H+ H+H +H+ H H ATP + +H+ H H+ + H+ H+H H H H

ETC of Photosynthesis Chloroplasts transform light energy into chemical energy of ATP u generates O 2 AP Biology use electron carrier NADPH

The ATP that “Jack” built photosynthesis sunlight respiration breakdown of C 6 H 12 O 6 H+ H+ moves the electrons runs the pumps the protons builds the gradient drives the flow of protons ADP + Pi through ATP synthase § bonds Pi to ADP ATP § generates the ATP AP Biology … that evolution built § § § H+ H+

Pigments of photosynthesis How does this molecular structure fit its function? § Chlorophylls & other pigments u u embedded in thylakoid membrane arranged in a “photosystem” § collection of molecules AP Biology u structure-function relationship

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

Light: absorption spectra § Photosynthesis gets energy by absorbing wavelengths of light u chlorophyll a § absorbs best in red & blue wavelengths & least in green u accessory pigments with different structures absorb light of different wavelengths § chlorophyll b, carotenoids, xanthophylls Why are plants green? AP Biology

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

ETC of Photosynthesis § ETC uses light energy to produce u ATP & NADPH § go to Calvin cycle § PS II absorbs light u u u AP Biology 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 § O 2 released to atmosphere § and we breathe easier!

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

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 u 18 ATP + NADPH AP 12 Biology 1 C 6 H 12 O 6 ATP

Photophosphorylation cyclic photophosphorylation NADP NONcyclic photophosphorylation ATP AP Biology

Photosynthesis: The Calvin Cycle Life from Air AP Biology 2007 -2008

Remember what it means to be a plant… § Need to produce all organic molecules necessary for growth u carbohydrates, lipids, proteins, nucleic acids § Need to store chemical energy (ATP) produced from light reactions in a more stable form u that can be moved around plant u saved a rainy day glucose + oxygen carbon + for water + energy u dioxide 6 CO 2 + 6 H 2 O + light C 6 H 12 O 6 + 6 O 2 energy AP Biology

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

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

From CO 2 C 6 H 12 O 6 § CO 2 has very little chemical energy u fully oxidized § C 6 H 12 O 6 contains a lot of chemical energy u highly reduced § Synthesis = endergonic process u put in a lot of energy § Reduction of CO 2 C 6 H 12 O 6 proceeds in many small uphill steps each catalyzed by a specific enzyme u using energy stored in ATP & NADPH u AP Biology

From Light reactions to Calvin cycle § Calvin cycle u chloroplast stroma § Need products of light reactions to drive synthesis reactions ATP u NADPH u ATP thylakoid AP Biology stroma

To G 3 P and Beyond! § Glyceraldehyde-3 -P To G 3 P and beyond! end product of Calvin cycle u energy rich 3 carbon sugar u “C 3 photosynthesis” u § G 3 P is an important intermediate § G 3 P glucose carbohydrates lipids phospholipids, fats, waxes amino acids proteins nucleic acids DNA, RNA AP Biology

Ru. Bis. Co § Enzyme which fixes carbon from air ribulose bisphosphate carboxylase u the most important enzyme in the world! u § it makes life out of air! definitely the most abundant enzyme It’s not easy u I’m green with envy! AP Biology being green!

Accounting § The accounting is complicated u 3 turns of Calvin cycle = 1 G 3 P u 3 CO 2 1 G 3 P (3 C) u 6 turns of Calvin cycle = 1 C 6 H 12 O 6 (6 C) u 6 CO 2 1 C 6 H 12 O 6 (6 C) u 18 ATP + 12 NADPH 1 C 6 H 12 O 6 u AP Biology any ATP left over from light reactions will be used elsewhere by the cell

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

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

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

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

even though this equation is a bit of a lie… it makes a better story Energy cycle sun Photosynthesis light CO 2 + H 2 O + energy C 6 H 12 O 6 + O 2 plants CO 2 H 2 O glucose animals, plants ATP C 6 H 12 O 6 + O 2 energy + CO 2 + H 2 O Cellular Respiration AP Biology The Great Circle of Life, Mufasa! ATP O 2

Supporting a biosphere § On global scale, photosynthesis is the most important process for the continuation of life on Earth u each year photosynthesis… § captures 121 billion tons of CO 2 § synthesizes 160 billion tons of carbohydrate u AP Biology 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 AP Biology sun Then all the plants, cats, dogs, elephants & people … are really particles of air woven together by strands of sunlight!