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5 Written Questions

5 Matching Questions

  1. Purine Biosynthesis Overview
  2. Anti virals, Acyclovir, AraA
  3. Anti neoplastics
  4. 8th step in pyrimidine biosynth CTP cynthetase
  5. Nucleoside Phosphorylases
  1. a Used for degradation

    Purine Nucleoside Phosphorylase has multiple substrates. Has a stronger affinity for Guo and Ino, and weak affinity for Ado, all are not phosphorylated

    It takes them all to Guanine, hypoxanthine, and adenine pluse a ribose 1 phosphate
  2. b Acyclovir, used to treat HSV infections, and is converted to triphosphate by enzymes including a viral nucleoside kinase with broad substrate specificity, and interferes with DNA synthesis in infected cells

    AraA tx for herpes related viral encephalitis. this is converted to triphosphates interferes with DNA synthesis, and is deaminated rapidly in vivo by ADA so is sometimes administered with a ADA inhibitor
  3. c CTP synthetase takes Nitrogen from Glutamine and ATP and makes CTP the base Cytosine with ribose and three phosphates.
  4. d some discussed earlier
    araC, triphosphate interferes with DNA synthesis
  5. e Starting point with PRPP, and activated ribose

    Purine ring is built up step by step while attached to ribose sugar

    forming IMP a nucleotide intermediate that can form either AMP or GMP

5 Multiple Choice Questions

  1. CPS II = takes CO2 and Gln to Carbamoyl P
    ATCase, committed step = take Carbamoyl P and Aspartate to N-Carbamoyl aspartate
    CTPS = takes UTP to CTP
  2. 6 mercaptopurine
    6 thiaguanine
    These compounds compete with hypoxanthine and guanine for the salvage enzyme HGPRT.
    They are converted by HGPRT into respective ribonucleotides, they inhibit the committed step of de novo purine biosynthesis pathway catalyzed by Gln PRPP amidotransferase, an effect similar to allopurinol
    They are also incorporated into DNA and RNA
  3. Ring closure no ATP

    Forms Di hydroorotase

    after NAD+ forms to orotate
  4. Allopurinol is a suicide inhibitor of xanthine oxidase, because it is similar in configuration to hypoxanthine and it binds tightly to molybdenum in xanthine oxidase.

    Xanthine oxidase takes Hypoxanthine to xanthine and xanthine to uric acid
  5. IMP uses NAD+ and H20 to oxidize and add carboxyl O to bottom left carbon making base xanthine

    Glutamine and ATP needed to replace carboxyl O with N. Forming GMP

5 True/False Questions

  1. Pyrimidine Synthesis Differences from PurinesIMP uses NAD+ and H20 to oxidize and add carboxyl O to bottom left carbon making base xanthine

    Glutamine and ATP needed to replace carboxyl O with N. Forming GMP


  2. Defects in Pyrimidine BiosynthesisFamilial Orotic Aciduria are inherited deficincies in orotate phosphoribosyltrandferase OPRT and or OMP decarboxylase

    These slow the formation of OMP from orotate, and UMP from OMP.

    Signs and symptomes are growth retardation, megaloblastic anemia, crystalline orotate in urine

    Tx effectively by large doses of orally administered uridine


  3. Sites of feedback regulation of Purine biosynthesisCTP inhibits two enzymes

    CTPS which forms CTP from UTP is inhibited by CTP, also it requires GTP so low GTP will slow CTP formation

    CPS II is the first reaction which forms carbamoyl P, and is inhibited by CTP


  4. First Step in Pyrimidine biosynth CPS IIusing Carbamoyl phosphate synthetase II, CPS II takes CO2 and Glutamine to Carbamoyl phosphate using 2 ATP

    In mitochondria CPS I uses NH4+ as a nitrogen source, this is part of the urea cycle


  5. Purine Nucleosid Phosphorylase PNP deficiencyanother rare cause of SCIDS Disorder, since Ino, dIno, Guo and dGuo are strong subtrates of PNP and Ado and dAdo is weak we get a larger build up of dAdo relative to dNTPs


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