Lecture_22_4-20-10-PDF_41870

Lecture_22_4-20-10-PDF_41870 - Amino Acid Metabolism 5....

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Amino Acid Metabolism 5. Amino acid biosynthesis 6. Other products of amino acid metabolism 7. Nitrogen fixation
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Nitrogen fixation N 2 + 8H + + 8e - + 16 ATP 2NH 3 + H 2 + 16ADP + 16 P i Bacteria Klebsiella , Azotobacter , cyanobacteria, rhizobium do this. Rhizobium form nodules (bacteroid which nitrogen is fixed). The nitrogen triple bond ~340 kJ/mole is hard to reduce. Requires the absence of Oxygen. Leghemoglobin (hemoprotein) binds oxygen so tight that it scrubs out all oxygen from the nodules.
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N 2 + 8H + + 8e - + 16 ATP 2NH 3 + H 2 + 16ADP + 16 P i Nitrogenase
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Nitrogenase contains two proteins Component I , Nitrogenase or the Molybdenum-Iron protein which catalyzes the reduction of N 2 . Component II , nitrogenase reductase, transfers electrons from ferredoxin or flavodoxin to component I.
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1. The reactions occur while N 2 is bound to the nitrogenase enzyme complex. 2. The Fe protein is first reduced by electrons donated by ferredoxin. 3. Then the reduced Fe protein binds ATP and reduces the molybdenum-iron protein, which donates electrons to N 2 , producing HN=NH. 4. In two further cycles of this process (each requiring electrons donated by ferredoxin) HN=NH is reduced to H 2 N-NH 2 , and this in turn is reduced to 2NH 3 . Electron transfer and ATP utilization of the nitrogenase enzyme N 2 + 8H + + 8e - + 16 ATP 2NH 3 + H 2 + 16ADP + 16 P i Component II Component I
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N 2 + 8H + + 8e - + 16 ATP 2NH 3 + H 2 + 16ADP + 16 P i
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e.g. glutathione peroxidases, tetraiodothyronine 5' deiodinases, thioredoxin reductases, formate dehydrogenases, glycine reductases and some hydrogenases. Selenocysteine (21 st amino acid, 1986) (BOX 27-2, p 1000) a structure similar to cysteine, but with an atom of selenium taking the place of the usual sulfur. 1. Selenocysteine is not coded for directly in the genetic code. Instead, it is encoded in a special way by a UGA codon, which is normally a stop codon. 2. The UGA codon is made to encode selenocysteine by the presence of a SECIS element (SElenoCysteine Insertion Sequence) in the mRNA. 3. The SECIS element is defined by characteristic nucleotide sequences and secondary structure base-pairing patterns. 4. In bacteria, the SECIS element is located immediately following the UGA codon within the reading frame for the selenoprotein. cys Supplemental
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22nd Amino Acid pyrrolysine pyrrolysine pyrroline Lysine Supplemental
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22nd Amino Acid Methanogen uses stop codon to genetically encode L-pyrrolysine Supplemental
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The Nobel Prize in Physiology or Medicine 1968 "for their interpretation of the genetic code and its function in protein synthesis" Robert W. Holley Har Gobind Khorana Marshall W. Nirenberg 1/3 of the prize 1/3 of the prize 1/3 of the prize USA USA USA Cornell University Ithaca, NY, USA University of Wisconsin Madison, WI, USA National Institutes of Health Bethesda, MD, USA b. 1922 d. 1993 b. 1922 (in Raipur, India) b. 1927
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Nucleotide metabolism (Lec 22-24) Chapter 22 1. Synthesis of Purine Ribonucleotides A. Synthesis of Inosine Monophosphate B. Synthesis of Adenine and Guanine Ribonucleotides C. Regulation of Purine Nucleotide Biosynthesis D. Salvage of Purines 2. Synthesis of Pyrimidine Ribonucleotides
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Lecture_22_4-20-10-PDF_41870 - Amino Acid Metabolism 5....

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