FINAL06-1.answ scheffler

FINAL06-1.answ scheffler - METABOLIC BIOCHEMISTRY BIBC102...

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METABOLIC BIOCHEMISTRY BIBC102 Winter 2006 Immo E. Scheffler FINAL EXAM All answers are to be written into the Blue Book. Leave the first inside page blank for scoring. There are 18 questions. Make sure that each answer is clearly identified with the question number at the top or left side of the page. ********************************************************************************** QUESTION 1. (16 points) a) [10] Draw a diagram illustrating the photosynthetic electron transport chain as it is found in green plants (Z scheme), at the level presented in class. Your diagram should include the following components (clearly labeled): photosystems I and II, reaction centers I and II, the manganese containing complex, pheophytin, plastoquinones A and B, plastocyanin, ferredoxin, the cyt b 6 f complex, and the ferredoxin-NADP + oxidoreductase.
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b) [1] Where does photooxidation occur? Photooxidation occurs at the reaction centers designated P680 and P700 c) [1] Where is the oxygen evolved? at the oxygen evolving complex (containing manganese) d) [4] Why do we need 8 photons per O 2 evolved? four electrons are released from two water molecules to make one molecule of oxygen; these four electrons are passed through photosystems I and II to make two molecules of NADPH. Each photosystem has to be oxidized four times with four photons in succession e) [2] Where does this system in chloroplasts most resemble a similar complex in mitochondria? the cytochrome b 6 f complex has a structure and has subunits very similar to complex III in mitochondria; protons are pumped here from the stroma into the lumen of the thylakoid membranes QUESTION 2. (6 points)
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In cyclic photophosphorylation only one photosystem is used. Which one? What is the alternate path for electrons used in this cyclic process? What is gained (produced) from this process? Which normal products of the light reactions are NOT produced in cyclic photophosphorylation? The photosystem used is photosystem I. Electrons are passed from ferredoxin to plastoquinone PQ B and then through the cyt b 6 f complex and plastocyanin to P700. This mechanism serves to produce ATP, but no oxygen is evolved and no NADPH is produced. QUESTION 3. (4 points) What is the relationship of exciton transfer to the role of the antenna chlorophylls and the reaction center? antenna chlorophylls absorb photons and the energy from these photons is then transferred by exciton transfer to the reaction center where photooxidation occurs. QUESTION 4. (6 points) Illustrate the reaction by which CO 2 is initially fixed in the Calvin (C 3 ) cycle. Include structures and names of all subtrates and final products. It is not necessary to show unstable intermediates. ribulose 1,5-bisphosphate + CO 2 + H 2 O ==> two 3-phosphoglycerates QUESTION 5. (16 points)
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The carbon fixation pathway in C 3 plants involves the enzyme “rubisco”; sometimes rubisco cannot distinguish between CO 2 and O 2 .
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