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5 Written questions

5 Matching questions

  1. Nucleoside Phosphorylases
  2. Pyrimidine Synthesis Differences from Purines
  3. Phophoribosyl transferases PRTs
  4. Other causes of mild orotic aciduria
  5. Series of steps for Purine after is PRA
  1. a Unbranched pathway
    Pyrimidine ring synthesized first then attached to ribose phosphate
  2. b PRA adds glycine, enzyme not important

    Methyl group added to N end of glycine with N10 formyl THF

    Glutamine adds N to replace carboxyl oxygen from glycine.

    First 5 point ring closes

    Biotin independent carboxylation with CO2

    Aspartate adds to carboxylated carbon with the N group first

    Fumarate leaves leaving N from Aspartate

    N10 formyl THF methylates lower N

    then there is low energy ring closure

    Makes IMP the base is called hypoxanthine
  3. c ammonia toxicity
    Ornithine transcarbamoylase def
    in both cases carbamoyl P accumulated in liver mitochondria, which enters cytoplasm, which drives overproduction of orotate via the pyrimidine biosynthesis pathway.
  4. d 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
  5. e Used for salvage

    Hypoxanthine Guanine PRT or HGPRT catalyzes 2 rxns

    PRPP and hypoxanthine to IMP plus PPi

    or PRPP plus Guanine to GMP plus PPi

    Adenine PRT , APRT

    PRPP plus adenine to AMP plus PPi.

5 Multiple choice questions

  1. using 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
  2. Thymidylate Synthetase uses N5N10 Methylene THF as a methyl transfer group to turn dUMP to dTMP, then becomes DHF which must be recycled
  3. some discussed earlier
    araC, triphosphate interferes with DNA synthesis
  4. 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. IMP uses Aspartate and GTP to add N in place of carboxyl O at top

    Fumarate leaves leaving just NH2 and AMP is formed

5 True/False questions

  1. Important Enzymes in Pyrimidine BiosynthCPS 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. Origins of Pyrimidine Ring AtomsFamilial 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. Anti virals, Acyclovir, AraAAcyclovir, 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


  4. Prokaryotic Regulation of Pyrimidine BiosynthCTP inhibits the action of ATCase the committed step and addition of aspartate to carbamoyl P

    and UMP inhibits the action of CPSII the first step and formation of Carbamoyl p


  5. Results of tx with allopurinalAllopurinol 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