Two Reactions of Photosynthesis Light Reaction aka light

Two Reactions of Photosynthesis Light Reaction aka light dependent rxn Transforming light photons into ATP and the electron carrier NADPH Calvin Cycle aka light independent reaction Use ATP/NADPH to make glucose 1

The Light Reaction • • • Occurs in the thylakoid membrane 2 Photosystems: I and II 2 Electron Transport Chains (ETC) Consumes H 2 O for protons, e. Generates O 2 ATP and NADPH 2

e- of cholorphyll ETC a is energized Photosystem II pigments direct energy to chlorophyll a which becomes oxidized ETC donates e-, reduces NADP+ to NADPH Photosystem I is energized

Concurrently to ETC: • H+ builds up in thylakoid From H 2 O, proton pump • H+ diffuse from high to low concentration through ATP synthase generating ATP

Proton pump driven by e- ETC H+ 2 H 2 O oxidized 4 H+ + O 2 Creating high proton concentration in the thylakoid (+ e-)

Inputs & Products • Radiant energy (visible wavelengths) • 2 H 2 O O 2 + 4 H (+ e-) At second ETC: • NADP+ + H NADPH Via chemiosmosis • ADP + P ATP 7

Chemiosmosis SUN H+ H + Thylakoid E PS II (Proton Pumping) T PS I C H 2 O H+ H+ H + H+ ADP + P H+ H+ high H+ concentration ATP Synthase ATP Thylakoid Space low H+ concentration 8

http: //www. stolaf. edu/people/giannini/flashanimat/metabolism/phot osynthesis. swf http: //www. science. smith. edu/departments/Biology/Bio 231/ltrxn. ht ml http: //www. youtube. com/watch? v=BK_cjd 6 Evcw http: //www. sumanasinc. com/webcontent/animations/content/harve stinglight. html

Cyclic Electron Flow Primary Electron Acceptor SUN ee- e. Photons P 700 e- ATP produced by ETC Accessory Pigments Photosystem I Pigments absorb light energy & excite e- of Chlorophyll a to produce ATP 10

Light Reaction (Electron Flow) During the light reaction, there are two possible routes for electron flow: A. Cyclic Electron Flow B. Noncyclic Electron Flow 11