Purines and Pyrimidine Metabolism Quiz
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Questions and Answers

What are the two main components of nucleotides?

  • Amino acids and fatty acids
  • Lipids and proteins
  • Sugar and phosphate groups (correct)
  • Purines and pyrimidines (correct)
  • What is the role of pancreatic juice in the digestion of nucleic acids?

  • It hydrolyses nucleic acids into mononucleotides (correct)
  • It absorbs nucleic acids
  • It converts nucleotides into pyrimidines
  • It synthesizes purines and pyrimidines
  • Which of the following is NOT a source of dietary purines and pyrimidines?

  • Liver and meat
  • Legumes and cereals
  • Tea, coffee, and cola
  • Egg, milk, and cheese (correct)
  • What is the importance of UDP-glucuronic acid in the body?

    <p>It acts as a donor for conjugation reactions</p> Signup and view all the answers

    Which of the following is a biomedical importance of purines and pyrimidines?

    <p>Energy metabolism</p> Signup and view all the answers

    What happens to ingested nucleic acids and nucleotides in the intestinal tract?

    <p>They are degraded to mononucleotides</p> Signup and view all the answers

    What is the term for the compounds formed from the linkage of a sugar with a nitrogen-containing base?

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

    Which of the following is a gout disease treatment?

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

    What is the primary function of nucleosidases?

    <p>Hydrolyze nucleosides into free bases and pentose</p> Signup and view all the answers

    What happens to unabsorbed purines in the gut?

    <p>They are converted to uric acid by intestinal bacteria</p> Signup and view all the answers

    What is the site of purine base catabolism?

    <p>Liver (intracytoplasmic)</p> Signup and view all the answers

    What is the end product of purine base catabolism in humans?

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

    What is the normal range of uric acid in females?

    <p>2-6mg/dl</p> Signup and view all the answers

    What is the underlying cause of gout?

    <p>Increased production and deposition of uric acid crystals</p> Signup and view all the answers

    What is Lesch-Nyhan syndrome inherited as?

    <p>X-linked recessive disorder</p> Signup and view all the answers

    What is the most painful manifestation of gout?

    <p>Acute gouty arthritis</p> Signup and view all the answers

    What is the primary cause of Lesch-Nyhan syndrome?

    <p>Deficiency of hypoxanthine-guanine phosphoribosyl transferase</p> Signup and view all the answers

    What is the composition of renal stones in gout?

    <p>Mainly composed of uric acid and/or urates</p> Signup and view all the answers

    In which organisms is ammonia the end product of protein catabolism?

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

    What is a common symptom of Lesch-Nyhan syndrome?

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

    What is hypouricemia due to?

    <p>Decreased uric acid formation</p> Signup and view all the answers

    What is the result of adenosine deaminase deficiency?

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

    What is the daily excretion of uric acid in urine?

    <p>0.7gm/day</p> Signup and view all the answers

    What is the effect of a purine-free diet on uric acid excretion?

    <p>Decreased excretion</p> Signup and view all the answers

    Which of the following statements about the catabolism of pyrimidines is TRUE?

    <p>β-alanine is the major end product of both uracil and cytosine.</p> Signup and view all the answers

    What is the main cause of β-amino isobutyric aciduria?

    <p>Defective deamination of β-aminoisobutyric acid.</p> Signup and view all the answers

    What are the characteristic symptoms of orotic aciduria?

    <p>Retarded growth, severe anemia, and leukopenia.</p> Signup and view all the answers

    What is the mechanism by which uridine and cytidine treat orotic aciduria?

    <p>They increase UMP production, which inhibits CPS-II and reduces orotic acid production.</p> Signup and view all the answers

    Which of the following conditions can lead to increased levels of β-aminoisobutyric acid in urine?

    <p>Leukemia.</p> Signup and view all the answers

    What is the role of Orotate phosphoribosyl transferase and Orotidine 5'-phosphate decarboxylase (OMP decarboxylase) in pyrimidine metabolism?

    <p>They are involved in the conversion of orotate to UMP.</p> Signup and view all the answers

    Which of the following statements about orotic aciduria Type I and Type II is TRUE?

    <p>Orotic aciduria Type I and Type II are caused by different genetic mutations but lead to the same clinical manifestations.</p> Signup and view all the answers

    Which of the following is NOT a characteristic of orotic aciduria?

    <p>Deficiency in purine metabolism.</p> Signup and view all the answers

    Study Notes

    Purines and Pyrimidines

    • Purines and pyrimidines are heterocyclic aromatic compounds that form the important components of nucleotides along with sugar and phosphate groups.
    • Purines include adenine and guanine, while pyrimidines include thymine, uracil, and cytosine.

    Nucleotide Structure

    • A nucleoside is formed from the linkage of a sugar with a nitrogen-containing base.

    Biomedical Importance

    • DNA and RNA are nucleic acids composed of purines and pyrimidines.
    • ATP and GTP are energy carriers.
    • NADH and FADH are co-enzymes.
    • S-Adenosyl-methionine is a donor for methyl groups.
    • UDP-glucuronic acids are donors for conjugation (e.g., bilirubin glucuronide).
    • cAMP and cGMP are involved in hormone signaling.
    • Anticancer drugs (e.g., MTX, 5-Flu, 6-TG, 6-MG) and antiviral drugs (e.g., Aciclovir, Lamivudine) are developed based on purine and pyrimidine metabolism.
    • Allopurinol is used to treat gout disease.

    Dietary Non-Essentiality

    • Human tissues can synthesize purines and pyrimidines, making them dietarily non-essential.
    • Ingested nucleic acids and nucleotides are degraded in the intestinal tract to mononucleotides, which may be absorbed or converted to purine and pyrimidine bases.
    • Dietary sources of purines and pyrimidines include liver, meat, legumes, cereals, and vegetables, as well as tea, coffee, cocoa, and cola.

    Purine and Pyrimidine Metabolism

    • Digestion and absorption: pancreatic juice contains nucleases that hydrolyze nucleic acids into mononucleotides, which are then broken down by nucleotidases and intestinal phosphatases.
    • Unabsorbed purines are converted to uric acid by intestinal bacteria, which may be absorbed and excreted in urine.

    Catabolism of Purine

    • Site: liver (intracytoplasmic)
    • Hypoxanthine is oxidized into xanthine, and further into uric acid by xanthine oxidase.
    • Uric acid diffuses to the blood to be excreted by the kidney.
    • Uric acid is the end product of purine base catabolism.

    Gout

    • Gout is a metabolic disorder related to excess production and deposition of uric acid crystals (hyperuricemia).
    • Hyperuricemia is characterized by recurrent attacks of acute inflammatory arthritis.
    • Normal blood uric acid levels are 3-7 mg/dl (males) and 2-6 mg/dl (females).
    • It is excreted in urine (0.7 gm/day), with decreased excretion in cases of purine-free diet.

    Lesch-Nyhan Syndrome

    • Lesch-Nyhan syndrome is an X-linked recessive disorder caused by defects in the activity of the purine nucleotide salvage enzyme, hypoxanthine-guanine phosphoribosyl transferase.
    • Causes: deficiency of the enzyme HGPRT, produced by mutations in the HPRT gene.
    • Symptoms: severe gout, kidney problems, poor muscle control, and moderate mental retardation.

    Hypouricemia

    • It may be renal (due to low renal threshold) or metabolic (due to decreased uric acid formation).
    • Causes of metabolic hypouricemia:
      • Deficiency of adenosine deaminase (adenosinuria)
      • Deficiency of xanthine oxidase (hypoxanthine and xanthine are excreted in excess in urine)
      • Deficiency of purine nucleosidase (accumulation of guanosine and inosine leading to guanosinuria)
      • Deficiency of folic acid (decreased de novo synthesis of purines)

    Catabolism of Pyrimidines

    • This occurs mainly in the liver.
    • β-Alanine is the major end product of both uracil and cytosine.
    • β-Amino isobutyric is the major end product of thymine.

    Disorders of Pyrimidine Metabolism

    • β-Amino isobutyric aciduria: characterized by excretion of large amounts of β-aminoisobutyric in urine, caused by defective deamination of β-aminoisobutyric acid.
    • Hereditary orotic aciduria:
      • Type I: caused by defective orotate phosphoribosyl transferase and orotidine 5'-phosphate decarboxylase, leading to retarded growth, severe anemia, and megaloblastic bone marrow.
      • Type II: caused by defective OMP decarboxylase, similar to Type I.

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    Description

    This quiz covers the components of nucleotides, including purines and pyrimidines, and their role in DNA and RNA. Test your knowledge of adenine, guanine, thymine, uracil, and cytosine.

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