ch369_f09_photo_2_notes

ch369_f09_photo_2_notes - Photosynthesis (continued) -...

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Photosynthesis (continued) - Chapter 13 Photosynthesis uses the energy of sunlight to convert CO 2 into carbohydrates and other useful organic molecules. chloroplasts Chloroplasts - where photosynthesis occurs.
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Photosynthesis includes “light reactions” and “dark reactions”. Dark reactions use the energy stored within ATP and NADPH for the synthesis of carbohydrates and other useful organic molecules from CO 2 . Light reactions (yesterday’s topic) use energy from sunlight to drive a series of oxidation-reduction reactions that result in the production of ATP and NADPH.
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Light reactions.
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A “ cyclic photoreaction ” also occurs at photosystem I. The cyclic reaction pumps protons from stroma to lumen , but does not reduce NADP + to NADPH. An electron excited by light in photosystem I is used to reduce Ferredoxin, which passes an electron to cytochrome b6f, and then to plastocyanin, and back to photosystem I. Dissipating energy pumps protons. Electron gets energy boost from absorbed photon.
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Energy released in the electron transport chain is used to pump H + from stroma into lumen. H + that accumulate in the lumen escape back to stroma by passing through ATP synthase, producing ATP.
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Chloroplasts use the energy of the proton gradient to make ATP. Similar to mitochondria.
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Summary up to this point: Photosystem II, cytochrome b6f, and Photosystem I work together to use light energy to: 1) Generate a pH gradient across the membrane separating stroma and lumen. The protons that are moved across the membrane are pulled from water, generating O 2 as a waste product. 2) Make ATP using ATP synthase. 1) Make NADPH (another high-energy molecule). All together, these are called the “light reactions”.
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Next, the “ dark reactions ”. Dark reactions = Using the energy stored in ATP and NADPH to convert CO 2 into useful things like sugars and other organic molecules needed for growing plants.
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ribulose bisphosphate carboxylase/oxygenase (or Rubisco ) catalyzes CO 2 fixation into carbohydrates. Rubisco adds CO
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This note was uploaded on 01/21/2010 for the course CH 369 taught by Professor Kbrowning during the Fall '07 term at University of Texas.

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ch369_f09_photo_2_notes - Photosynthesis (continued) -...

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