BIO 101 1st Edition Lecture 15 Outline of Last Lecture I Fermentation a Products of glycolysis II Respiration III Photosynthesis a Calvin cycle b Light reactions Outline of Current Lecture I Calvin Cycle II Light Reactions a Photosystem I b Photosystem II III The Circle of Life Chapter 10 cont Calvin Cycle Called a cycle because one of the beginning reactant RuBP is regenerated Anabolic pathway requires ATP both come from Reduction requires source of electrons light reactions Light Reactions Conversion of light energy to make ATP and a reduced coenzyme NADPH Occurs on thylakoid membranes of chloroplast Uses 2 photosystems light harvesting units on the thylakoid membranes o Group of 200 300 pigment molecules arranged like an ANTENNA to capture light energy Photosystem I PSI and Photosystem II PSII Three kinds of pigments chlorophyll A B carotenoids PSI and PSII have slightly different populations of pigments and capture light energy of slightly different wavelengths BIO 101 1st Edition The two photosystems are connected by an electron transport chain Coenzyme oxidized from NADP is converted to NADPH reduced form available to donate electrons to Calvin Cycle The electrons are knocked off PSII by light and transferred along electron transport chain via PSI eventually to NADP NADPH PSII electrons are replaced by H2O H2O splitting reaction electrons go to PSII H go into thylakoid space O2 is released as gas H are also transferred into the thylakoid space as electrons are passed along electron transport chain that connects PSII to PSI H gradient results from H2O splitting reaction and from electron transport chain PROTON MOTIVE FORCE ATP is produced by chemiosmosis using energy of a proton gradient to make ATP The photosynthetic ATP synthase is on the thylakoid membrane and produces ATP in the stroma The Circle of Life Connection between respiration and photosynthesis Products of one are the beginning reactants of the other BIO 101 1st Edition Without photosynthesis all living things would die run out of food and oxygen
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