Heme Synthesis and Porphyrias
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Questions and Answers

Which enzyme defect is responsible for the accumulation of tetrapyrrole intermediates, leading to photosensitivity?

  • Uroporphyrinogen III decarboxylase
  • Coproporphyrinogen III oxidase
  • Protoporphyrinogen oxidase (correct)
  • Hydroxymethylbilane synthase
  • Which type of porphyria is characterized by abdominal pain, neuropsychiatric disturbances, and photosensitivity?

  • Hereditary Coproporphyria (correct)
  • Acute Intermittent Porphyria
  • Variegate Porphyria
  • Porphria Cutanea Tarda
  • What is the primary site of accumulation of porphyrins or porphyrin precursors in erythropoietic porphyrias?

  • Bone marrow (correct)
  • Liver
  • Skin
  • Kidneys
  • Which enzyme is responsible for the conversion of hydroxymethylbilane to uroporphyrinogen III?

    <p>Uroporphyrinogen III synthase</p> Signup and view all the answers

    Which porphyria is characterized by abdominal pain and neuropsychiatric disturbances, but not photosensitivity?

    <p>Acute Intermittent Porphyria</p> Signup and view all the answers

    What is the primary site of accumulation of porphyrins or porphyrin precursors in hepatic porphyrias?

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

    Which enzyme is responsible for the final step of heme synthesis?

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

    What is the primary characteristic of chronic hepatic porphyrias?

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

    Which of the following statements about porphyrias is TRUE?

    <p>Porphyrias are rare, inherited defects in heme synthesis.</p> Signup and view all the answers

    What is the key distinction between acute hepatic porphyrias and chronic hepatic porphyrias?

    <p>The duration of symptoms.</p> Signup and view all the answers

    Which enzyme is involved in the conversion of hydroxymethylbilane to uroporphyrinogen III?

    <p>Uroporphyrinogen III synthase</p> Signup and view all the answers

    What is the common feature of all hepatic porphyrias?

    <p>Deficiency of an enzyme in the heme synthetic pathway.</p> Signup and view all the answers

    Which of the following porphyrias is NOT characterized by abdominal pain?

    <p>Porphria Cutanea Tarda</p> Signup and view all the answers

    What is the final product of the heme synthetic pathway?

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

    Which of the following enzymes is involved in the conversion of coproporphyrinogen III to protoporphyrinogen?

    <p>Coproporphyrinogen III oxidase</p> Signup and view all the answers

    Which type of porphyria is characterized by the accumulation of porphyrins or porphyrin precursors in the liver?

    <p>Hepatic porphyrias</p> Signup and view all the answers

    Study Notes

    Heme Synthesis and Porphyrias

    • Porphyrias are rare, inherited or acquired defects in heme synthesis, resulting in the accumulation and increased excretion of porphyrins or porphyrin precursors.
    • Each porphyria results in the accumulation of intermediates caused by the deficiency of an enzyme in the heme synthetic pathway.

    Classification of Porphyrias

    • Erythropoietic porphyrias
    • Hepatic porphyrias, which include:
      • Acute hepatic porphyrias
      • Chronic hepatic porphyrias

    Clinical Manifestations of Porphyrias

    • Enzyme deficiency prior to tetrapyrrole synthesis leads to abdominal and neuropsychiatric signs.
    • Enzyme deficiency leading to accumulation of tetrapyrrole intermediates leads to photosensitivity.

    Heme Synthesis Pathway Enzymes

    • ALAS1 (ALA synthase)
    • ALA dehydratase
    • Hydroxymethylbilane synthase (HMBS)
    • Uroporphyrinogen III synthase
    • Uroporphyrinogen III decarboxylase
    • Coproporphyrinogen III oxidase
    • Protoporphyrinogen oxidase
    • Ferrochelatase

    Types of Porphyria

    Hepatic Porphyrias

    • Acute Intermittent Porphyria (AIP): deficiency of Hydroxymethylbilane synthase, characterized by abdominal pain and neuropsychiatric disturbances.
    • Porphyria Cutanea Tarda (PCT): deficiency of Uroporphyrinogen III decarboxylase, characterized by photosensitivity.
    • Hereditary Coproporphyria: deficiency of Coproporphyrinogen III oxidase, characterized by abdominal pain, neuropsychiatric disturbances, and photosensitivity.
    • Variegate Porphyria (VP): deficiency of Protoporphyrinogen oxidase.

    Heme Synthesis and Porphyrias

    • Porphyrias are rare, inherited or acquired defects in heme synthesis, leading to the accumulation and increased excretion of porphyrins or porphyrin precursors.
    • Each porphyria results from the deficiency of an enzyme in the heme synthetic pathway, causing the accumulation of intermediates.

    Classification of Porphyrias

    • Erythropoietic porphyrias
    • Hepatic porphyrias, which are further divided into:
      • Acute hepatic porphyrias
      • Chronic hepatic porphyrias

    Clinical Manifestations of Porphyrias

    • If enzyme deficiency occurs before tetrapyrrole synthesis, abdominal and neuropsychiatric signs occur.
    • If enzyme deficiency leads to tetrapyrrole intermediate accumulation, photosensitivity occurs.

    Enzymes in Heme Synthesis

    • ALAS1 (ALA synthase)
    • ALA dehydratase
    • Hydroxymethylbilane synthase (HMBS)
    • Uroporphyrinogen III synthase
    • Uroporphyrinogen III decarboxylase
    • Coproporphyrinogen III oxidase
    • Protoporphyrinogen oxidase
    • Ferrochelatase

    Types of Porphyrias

    • Acute Intermittent Porphyria (AIP):
      • Enzyme defect: Hydroxymethylbilane synthase
      • Signs: Abdominal pain, neuropsychiatric disturbances
    • Porphyria Cutanea Tarda (PCT):
      • Enzyme defect: Uroporphyrinogen III decarboxylase
      • Signs: Photosensitivity
    • Hereditary Coproporphyria:
      • Enzyme defect: Coproporphyrinogen III oxidase
      • Signs: Abdominal pain, neuropsychiatric disturbances, photosensitivity
    • Variegate Porphyria:
      • Enzyme defect: Protoporphyrinogen oxidase
      • Signs: Abdominal pain, neuropsychiatric disturbances, photosensitivity

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    Description

    This quiz covers the production of heme, a crucial molecule in the body, and porphyrias, a group of rare disorders caused by defects in heme synthesis. Learn about the enzyme deficiencies that lead to these conditions.

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