STUDY_SHEET_Lectures_13-18

STUDY_SHEET_Lectures_13-18 - BIS 103 STUDY SHEET for...

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BIS 103 STUDY SHEET: for FINAL (FALL 2007) Nitrogen Metabolism and the Nitrogen Cycle 1. N 2 --> NH 3 (reducing nitrogen gas to ammonia) 2. N-N (triple) bond energy (942 KJ/mol) – very stable and unreactive 3. Biological N fixation (30°C, 1 atm, 8e's, 8H + ); Haber industrial process (500°C, 200 atm, 6e's, 6H + ); why 8 e- for biological N fixation and only 6 for industrial production? 4. NO (nitrous oxide), NO 2 (nitric oxide), N 2 O 4 (Nitrogen tetroxide), NO 3 - (nitrate), NO 2 - (nitrite); N 2 + O 2 = 2 NO; 2 NO + O 2 = 2 NO 2 ; 2 NO 2 dimerize = N 2 O 4 ; N 2 O 4 + H 2 O = HNO 2 + HNO 3 . 5. Nitrosomonas (oxidizes NH 3 ---> NO 2 - ) ( G = -280 KJ/mol); Nitrobacter (oxidizes NO 2 - ---> NO 3 - ) ( G = -73 KJ/mol). These organisms use NO 2 - and NO 3 - as sources of energy. 6. Most plants take up NO 3 - and reduce it to NH 3 with reductases, since NH 3 is the form of nitrogen that is assimilated into organic compounds. 7. Fertilizer with NH 3 (bacteria convert it to NO 3 - , so plants can take it up). 8. Look at the figure on page 57 and understand it beyond what has been written above. Nitrogen Fixation 1. Phosphoroclastic reactions provide the necessary energy (ATP) and reducing power (Fdred) to convert N 2 ---> NH 3 . Also it provides H + . 2. Overall phosphoroclastic rxn: Pyr + ADP + Pi +Fd ox ---> Fdred + acetate + CO 2 + ATP + 2H + . 3. 100 moles pyruvate needed to fix 1 mol of N 2 ; no stoichiometry 4. Know the phosphoroclastic reaction enzymes, substrates, products, etc. 5. Be able to explain what is happening on p. 58 in the booklet and answer questions on p. 59. 6. DNR, DN, FeMoCo are sensitive to oxygen. 7. FeMoCo (iron, molybdenum, cofactor) – part of DN 8. DNR picks up electrons from Fdred, binds to DN and transfers electrons to DN. 9. DNR, DN are non-heme iron proteins/enzymes. 10. ATP binds to DNR and reduces the redox potential from -0.25 to -0.4 V, therefore it is easier to pass electrons to DN. 11. DNred contains the active site for N 2 binding, it's a slow acting enzyme, it may comprise as much as 5% of the cell protein. 12. Energy is wasted because 2e’s out of 8e's are used to make hydrogen gas (H 2 ). 13. nif genes code for DNR and DN (regulated by NH 3 , ADP). 14. Why is it hard to convert non-N fixing plants to N fixing plants? 15. Be able to answer the questions on pg 59. Nitrogen Assimilation Into Amino Acids 1. Ammonia is incorporated into AA's through glutamate and glutamine. Know structures, enzymes, and cofactors of these three reactions: glutamine synthetase, glutamate synthase, glutamate transaminase (bottom of p. 55).
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2. Know the structures of pyridoxol (Vit. B6), pyridoxal-P (co-factor), and pyridoxamine-P (transient form), especially the active site. 3.
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This note was uploaded on 04/19/2008 for the course BIS 103 taught by Professor Abel during the Spring '08 term at UC Davis.

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STUDY_SHEET_Lectures_13-18 - BIS 103 STUDY SHEET for...

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