Amino Acid and Nucleotide Biosynthesis
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Questions and Answers

What initiates the biosynthesis of heme?

  • Bilirubin and biliverdin
  • Uroporphyrinogen and enzymes
  • Albumin and erythrocytes
  • SuccinylCoA and glycine (correct)

    • Which compound accumulates due to defects in heme biosynthesis?

  • Bilirubin
  • Uroporphyrinogen (correct)
  • Biliverdin
  • Heme oxygenase

    • What effect does uroporphyrinogen accumulation have on urine?

  • It becomes bright yellow.
  • It remains unchanged.
  • It becomes completely colorless.
  • It turns purple to dark purplish. (correct)

    • What is the function of heme oxygenase in heme degradation?

    <p>Linearizes heme to create biliverdin.</p> Signup and view all the answers

    What potential craving might occur due to porphyrias?

    <p>For heme</p> Signup and view all the answers

    What is the precursor for the biosynthesis of glutamine?

    <p>Glutamate</p> Signup and view all the answers

    Which form of vitamin B6 is crucial for transamination reactions?

    <p>Pyridoxal phosphate</p> Signup and view all the answers

    Which amino acid is synthesized from the pyruvate precursor?

    <p>Alanine</p> Signup and view all the answers

    What is the role of PLP in amino acid synthesis?

    <p>Forming Schiff bases with lysine</p> Signup and view all the answers

    Which of the following amino acids is classified as non-essential in mammals?

    <p>Aspartate</p> Signup and view all the answers

    Which biosynthetic family does proline belong to based on its precursor?

    <p>α-Ketoglutarate</p> Signup and view all the answers

    Which amino acid is synthesized from ribose 5-phosphate?

    <p>Histidine</p> Signup and view all the answers

    Which metabolic pathway does serine originate from?

    <p>Glycolysis</p> Signup and view all the answers

    What is the primary pigment of urine, which is derived from bilirubin degradation?

    <p>Urobilin</p> Signup and view all the answers

    Which condition is most commonly associated with jaundice due to bilirubin accumulation?

    <p>Liver disease</p> Signup and view all the answers

    What role does UDP-glucuronosyl transferase (UDPGT) play in bilirubin metabolism?

    <p>It converts bilirubin to a water-soluble form for excretion.</p> Signup and view all the answers

    What is the initial substrate for de-novo purine synthesis?

    <p>PRPP</p> Signup and view all the answers

    What inhibits the rate-limiting enzyme in purine biosynthesis?

    <p>6-mercaptopurine</p> Signup and view all the answers

    In pyrimidine biosynthesis, what is the first step in synthesizing the pyrimidine ring?

    <p>Formation of orotate from carbamoyl phosphate and aspartate</p> Signup and view all the answers

    Which of the following products is a result of the intestinal microbiota acting on bilirubin degradation?

    <p>Stercobilin</p> Signup and view all the answers

    What is the significance of light in phototherapy for infant jaundice?

    <p>It converts toxic forms of bilirubin into non-toxic products.</p> Signup and view all the answers

    What is the role of ribonucleotide reductase in nucleotide metabolism?

    <p>It reduces the 2' C-OH bond to a 2'-H bond.</p> Signup and view all the answers

    Which anticancer drug inhibits thymidylate synthase?

    <p>5-fluorouracil (5FU)</p> Signup and view all the answers

    What is the result of a total lack of hypoxanthine-guanine phosphoribosyl transferase (HGPRT)?

    <p>Impaired salvage pathway for purines.</p> Signup and view all the answers

    What is the final product of the oxidation of hypoxanthine and xanthine?

    <p>Uric acid</p> Signup and view all the answers

    Which enzyme is responsible for converting dihydrofolate (DHF) to tetrahydrofolate (THF)?

    <p>Dihydrofolate reductase (DHFR)</p> Signup and view all the answers

    What condition is primarily caused by excess uric acid in the human body?

    <p>Gout</p> Signup and view all the answers

    Which of the following foods should be avoided to help treat gout?

    <p>Seafood and liver</p> Signup and view all the answers

    What type of drugs are allopurinol and febuxostat classified as in the treatment of gout?

    <p>Xanthine oxidase inhibitors</p> Signup and view all the answers

    What enzyme deficiency is associated with gout, particularly in the salvage pathway?

    <p>HGPRT</p> Signup and view all the answers

    Which compound is produced from the catabolism of pyrimidines?

    <p>Ammonia</p> Signup and view all the answers

    Which of the following CNS active compounds is synthesized from amino acids?

    <p>Histamine</p> Signup and view all the answers

    What is the primary source of ammonia in amino acid biosynthesis?

    <p>Deamination of amino acids</p> Signup and view all the answers

    What role does porcine uric acid oxidase play in the treatment of gout?

    <p>Converter of uric acid to allantoin</p> Signup and view all the answers

    Study Notes

    Amino Acid and Nucleotide Biosynthesis

    • Biosynthesis involves multiple steps, starting from precursors like glucose, 3-phosphoglycerate, phosphoenolpyruvate, and pyruvate.
    • Various amino acids are synthesized from these intermediates, including tryptophan, phenylalanine, tyrosine, alanine, valine, leucine, isoleucine, etc.
    • The citric acid cycle and pentose phosphate pathway are also involved in the process.
    • Bacteria can synthesize all 20 amino acids, while mammals require some from their diet.
    • Non-essential amino acids are made from ammonia and keto acids via transamination.
    • Transamination reactions utilize pyridoxal phosphate (PLP), an active form of vitamin B6.

    Ammonia Incorporation

    • Glutamine is formed from glutamate in a two-step enzymatic process using glutamine synthetase.
    • Glu phosphorylation creates a good leaving group, enabling ammonia substitution.

    Biosynthesis of Special Amino Acids, Biogenic Amines, and CNS-Active Compounds

    • Some amino acids are crucial building blocks of biogenic amines and central nervous system (CNS) active compounds.
    • These include tyrosine, tryptophan, and histidine.
    • These compounds are decarboxylated using PLP-dependent enzymes.

    Biosynthesis of Porphyrins

    • Porphyrin biosynthesis begins with succinyl CoA and glycine.
    • The process leads to the formation of porphyrins, including heme.
    • Enzyme deficiencies during this pathway can cause porphyrias.

    Defects in Heme Biosynthesis and Porphyrias

    • Mutations or malfunctions in heme biosynthesis enzymes cause porphyrias.
    • Precursors accumulate in blood cells, body fluids, and liver tissue.
    • Porphyrias are associated with urine discoloration, teeth fluorescence under UV light, and skin sensitivity to UV light.

    Heme Degradation and Bile Pigments

    • Degradation of heme produces biliverdin, a green compound.
    • Biliverdin is converted to bilirubin, a yellow compound.
    • Bilirubin travels through the bloodstream, bound to serum albumin.
    • Bilirubin is further broken down into urobilin and stercobilin.
    • Accumulation of bilirubin leads to jaundice.

    Purine Biosynthesis

    • A sugar (PRPP) and multiple units are added to form a complete nucleotide.
    • Glutamine-PRPP amidotransferase is a rate-limiting step, inhibited by certain anticancer drugs like 6-mercaptopurine and 6-thioguanine.

    Pyrimidine Biosynthesis

    • Pyrimidine synthesis begins with the creation of the pyrimidine ring (orotate) followed by attachment to ribose-5-phosphate.
    • Aspartate and carbamoyl phosphate provide the atoms for the ring structure.
    • UMP is phosphorylated to UTP, and UTP can be converted to CTP.

    Ribonucleotides to Deoxynucleotides

    • The 2' carbon hydroxyl group on ribonucleotides is directly reduced to a 2' hydrogen via ribonucleotide reductase.
    • The reducing agent is NADPH using glutathione and FAD.
    • Reduction happens to NDPs.

    dTMP from dUMP

    • Thymidylate synthase catalyzes the reaction to convert dUMP to dTMP.
    • 5-fluorouracil and other drugs target thymidylate synthase for anticancer therapies.

    Pyrimidine and Purine Degradation

    • Nucleases degrade DNA and RNA into nucleotides.
    • Excess nucleotides undergo catabolism through specific pathways (salvage).
    • Hypoxanthine-guanine phosphoribosyltransferase (HGPRT) is essential for re-using purine bases.
    • A deficiency in HGPRT causes Lesch-Nyhan syndrome.
    • Purines are degraded to uric acid, while pyrimidines generate NH4+ and urea, along with CAC intermediates like succinyl CoA.

    Excess Uric Acid and Gout

    • Excess uric acid causes gout (sodium urate crystal deposits in joints, usually toes).
    • Treatment options include avoiding purine-rich foods and using xanthine oxidase inhibitors like allopurinol.
    • Other therapies involve administering porcine uric acid oxidase.

    Overview Summary

    • Many metabolic pathways are involved in amino acid and nucleotide biosynthesis.
    • Defects in these pathways can result in various diseases.
    • The degradation of these molecules is also important for proper cellular function.

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    Related Documents

    Amino Acid and Nucleotide Biosynthesis Lecture Notes PDF

    Description

    This quiz covers the biosynthesis of amino acids and nucleotides, discussing pathways from various precursors and the involvement of the citric acid cycle. It explores the synthesis of essential and non-essential amino acids, particularly in bacteria and mammals, along with biochemical reactions such as transamination. Test your knowledge on this fundamental aspect of biochemistry.

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