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

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

<p>Energy metabolism (C)</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 (B)</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 (A)</p> Signup and view all the answers

Which of the following is a gout disease treatment?

<p>Allopurinol (C)</p> Signup and view all the answers

What is the primary function of nucleosidases?

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

What is the site of purine base catabolism?

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

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

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

What is the normal range of uric acid in females?

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

What is the underlying cause of gout?

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

What is Lesch-Nyhan syndrome inherited as?

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

What is the most painful manifestation of gout?

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

What is the primary cause of Lesch-Nyhan syndrome?

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

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

<p>Fishes (C)</p> Signup and view all the answers

What is a common symptom of Lesch-Nyhan syndrome?

<p>Dystonia (B)</p> Signup and view all the answers

What is hypouricemia due to?

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

What is the result of adenosine deaminase deficiency?

<p>Adenosinuria (B)</p> Signup and view all the answers

What is the daily excretion of uric acid in urine?

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

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

<p>Decreased excretion (D)</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. (A)</p> Signup and view all the answers

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

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

What are the characteristic symptoms of orotic aciduria?

<p>Retarded growth, severe anemia, and leukopenia. (B)</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. (A)</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. (D)</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. (C)</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. (D)</p> Signup and view all the answers

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

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

Flashcards

Purines and Pyrimidines

Heterocyclic aromatic compounds that, along with sugar and phosphate groups, are components of nucleotides.

Purines

Adenine and guanine, double-ring structures.

Pyrimidines

Thymine, uracil, and cytosine; single-ring structures.

Nucleoside

A sugar linked to a nitrogen-containing base.

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Purines and Pyrimidines Importance

DNA and RNA are composed of these.

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Purine/Pyrimidine Non-Essentiality

Body can synthesize; not essential in diet.

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Pancreatic Nucleases

Hydrolyze nucleic acids into mononucleotides

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Uric Acid Formation

Converted from unabsorbed purines by intestinal bacteria.

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Purine Catabolism Site

Liver (intracytoplasmic)

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Xanthine Oxidase

Enzyme that oxidizes hypoxanthine into xanthine, then to uric acid.

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Uric Acid

End product of purine base catabolism.

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Gout

Excess uric acid deposition, causing arthritis.

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Hyperuricemia

Recurrent attacks of acute inflammatory arthritis.

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Lesch-Nyhan Syndrome

An X-linked recessive disorder due to HGPRT deficiency.

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Lesch-Nyhan Cause

Deficiency of HGPRT.

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Lesch-Nyhan Symptoms

Severe gout, kidney problems, poor muscle control, mental retardation.

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Hypouricemia

Low uric acid levels in the blood.

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Hypouricemia Causes

May be due to low renal threshold or decreased uric acid formation.

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Xanthine Oxidase Deficiency

Deficiency leads to excess excretion of hypoxanthine and xanthine in urine.

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β-Alanine

Uracil and cytosine catabolism end product.

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β-Amino Isobutyric Acid

Thymine catabolism end product.

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β-Amino Isobutyric Aciduria

Excretion of large amounts of β-aminoisobutyric in urine.

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Hereditary Orotic Aciduria Type I

Defective orotate phosphoribosyltransferase and orotidine 5'-phosphate decarboxylase.

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Hereditary Orotic Aciduria Type II

Defective OMP decarboxylase.

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Hereditary Orotic Aciduria Symptoms

Retarded growth, severe anemia, megaloblastic bone marrow.

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What are the main Purines?

Purines include?

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What are the main Pyrimidines?

Pyrimidines include?

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Dietary source of Purines and Pyrimidines

Source in liver, meats, and legumes

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What is Gout?

A metabolic disorder linked to high levels of uric acid

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Catabolism location of pyrimidines

Where does catabolism of Pyrimidines occur?

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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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Purines and Pyrimidines Metabolism PDF

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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