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5 Written questions

5 Matching questions

  1. Purine biosynthesis IMP to AMP
  2. Second Step in Pyrimidine biosynth ATCase
  3. Deoxyribonucleotide dNTP biosynthesis
  4. Anti retrovirals
  5. De nove purine biosynthesis is expensive, how much and what do we do
  1. a Committed Step, and an allosteric enzyme

    Using Aspartate Transcarbamoylase, ATCase takes Carbamoyl Phosphate to N-carbamoyl aspartate adding aspartate
  2. b AZT, DDC, ddI
    Used to treat HIV and AIDS
    Triphosphates inhibit retroviral reverse transcriptase
  3. c Uses Ribonucleotide Reductase to take A,G,C,UDP to dA,dG,dC,dUDP

    All can form to triphosphate form easily

    Formation of dTMP and dTTP requires Thymidylate Synthetase, which is dependent on THF cycle and dihydrofolate reductase.
  4. d 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. e For AMP 8 high energy phosphates, 2 Gln, 1 Gly, 2 Asp

    For GMP 7 high energy phosphates, 3 Gln, 1 Gly, 1 Asp

    Thus we Regulate and use salvage pathways to recycle purines

5 Multiple choice questions

  1. Antivirals, acyclovir, Arabinosyladenine araA, for HSV and herpes related viral encephalitis
    Anti retrovirals, AZT, DDC, ddI for HIV
    Anti neoplastics, arabinosylcytosine araC
    Anti Leukemics, 6 mercaptopurin, 6 thiaguanine
  2. N1, C4,5,6= all from Aspartate
    C2, N3 = all from Carbamoyl phosphate
  3. Signs and Symptoms young with hematuria, megaloblastic anemia, hyperuricemia, crystals in urine, mental retardation, decreased gross motor function, and self mutilation, gout in early 20s

    is a Rare X linked disorder 1/400000 males, milder form = 8% kelly-seegmiller syndrome

    Cause = near total deficiency of HGPRT about 2% of activity

    biochemical consequenses
    Overproduction or urate
    Elevated PRPP concentrations
    Marked increase in rate of de novo purine biosynth
  4. Purine biosynthesis regulation and secondary causes

    Increased activity of PRPP synthetase increases conc of PRPP

    Increased activity of PRPP amido transferase

    also Partial loss of activity of HGPRT salvage enzyme
  5. rather than directly inhibiting Thymidylate Synthetase TS is inhibits the cyclical production of the methyl donor N5N10 methylene THF

    It does this by inhibiting the enzyme DHFR dihydrofolate reductase. Stopping the reduction of Dihydrofolate to THF, which is a needed substrate for N5N10 methylene THF

5 True/False questions

  1. First Step in Pyrimidine biosynth CPS IIOPRT takes orotate and PRPP and adds ribose P to make OMP


  2. Sixth step OMP decarboxylaseUsed 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


  3. 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


  4. Why allopurinal decreases rate of purine biosynthesisATP and GTP allosterically inhibit formation of PRPP from pentose phosphate pathway

    IMP, AMP and GMP allosterically inhibit PRPP amidotransferase, the committed step of the pathway with adds a N from Glutamine to PRPP

    AMP and GMP allosterically inhibit the first step in their own formation from IMP

    ATP and GTP are require for each others formation a non-allosteric type of biofeedback


  5. Nucleoside PhosphorylasesClinical use of nucleotide analogs usually is restricted to bases and nucleoside since phosphorylated nucleotides are poorly transported into cells

    They rely on tricking cellular or viral enzymes into phosphorylating nucleosides into metabolically active nucleotide forms, or converting bases into nucleotides vis salvage pathways