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Questions and Answers
Which enzyme deficiency leads to the accumulation of uroporphyrin I and coproporphyrin I in the urine?
Which enzyme deficiency leads to the accumulation of uroporphyrin I and coproporphyrin I in the urine?
- Ferrochelatase
- Porphobilinogen deaminase (correct)
- Uroporphyrinogen III cosynthetase
- Coproporphyrinogen oxidase
In which type of porphyria does a deficiency in uroporphyrinogen III cosynthetase lead to the accumulation of uroporphyrin I and coproporphyrin I in the urine?
In which type of porphyria does a deficiency in uroporphyrinogen III cosynthetase lead to the accumulation of uroporphyrin I and coproporphyrin I in the urine?
- Porphyria cutanea tarda
- Acute intermittent porphyria (correct)
- Erythropoietic protoporphyria
- Variegate porphyria
Which enzyme is inhibited by lead poisoning, leading to decreased heme synthesis and subsequent microcytic hypochromic anemia?
Which enzyme is inhibited by lead poisoning, leading to decreased heme synthesis and subsequent microcytic hypochromic anemia?
- Ferrochelatase (correct)
- Coproporphyrinogen oxidase
- Uroporphyrinogen III cosynthetase
- Porphobilinogen deaminase
Which enzyme defect results in the accumulation of coproporphyrin III and protoporphyrin IX, causing photosensitivity and skin fragility?
Which enzyme defect results in the accumulation of coproporphyrin III and protoporphyrin IX, causing photosensitivity and skin fragility?
Which enzyme is responsible for the synthesis of porphobilinogen from 2 ALA?
Which enzyme is responsible for the synthesis of porphobilinogen from 2 ALA?
What characteristic side chains and linkers are generated during the condensation of 2 ALA to porphobilinogen?
What characteristic side chains and linkers are generated during the condensation of 2 ALA to porphobilinogen?
Where do the oxidation steps, converting methyl groups to methine groups, take place?
Where do the oxidation steps, converting methyl groups to methine groups, take place?
Which enzyme is the same as Porphobilinogen Deaminase?
Which enzyme is the same as Porphobilinogen Deaminase?
What is the function of Ferrochelatase in heme synthesis?
What is the function of Ferrochelatase in heme synthesis?
Which porphyria results in the formation of zinc protoporphyrin (ZnPP) and leads to anemia?
Which porphyria results in the formation of zinc protoporphyrin (ZnPP) and leads to anemia?
Which porphyria is characterized by skin eruptions and discolored urine?
Which porphyria is characterized by skin eruptions and discolored urine?
What is the major pathophysiology of porphyrias?
What is the major pathophysiology of porphyrias?
Where does heme conversion to bilirubin take place?
Where does heme conversion to bilirubin take place?
What is the product of Heme Degradation by Heme Oxygenase?
What is the product of Heme Degradation by Heme Oxygenase?
What is a characteristic symptom of jaundice?
What is a characteristic symptom of jaundice?
Which proteins contain heme as a tightly bound prosthetic group?
Which proteins contain heme as a tightly bound prosthetic group?
What is the primary function of cytochrome P-450?
What is the primary function of cytochrome P-450?
Where is heme synthesized principally?
Where is heme synthesized principally?
What stimulates the process of erythropoiesis?
What stimulates the process of erythropoiesis?
Which enzyme is the rate-limiting step of heme synthesis?
Which enzyme is the rate-limiting step of heme synthesis?
What is the effect of low iron on ALAS2 production?
What is the effect of low iron on ALAS2 production?
Which disorder is due to an ALAS2 deficiency?
Which disorder is due to an ALAS2 deficiency?
What acts as a concentration-dependent inducer of aminolevulinic acid (ALA) synthase and porphobilinogen (PBG) deaminase in normal human bone marrow?
What acts as a concentration-dependent inducer of aminolevulinic acid (ALA) synthase and porphobilinogen (PBG) deaminase in normal human bone marrow?
Which type of porphyrins are physiologically relevant for people?
Which type of porphyrins are physiologically relevant for people?
What are porphyrinogens?
What are porphyrinogens?
What does hemin do to ALAS1 in the liver?
What does hemin do to ALAS1 in the liver?
What is the effect of drugs like phenobarbital on ALA synthase activity?
What is the effect of drugs like phenobarbital on ALA synthase activity?
Which liver disease results from a reduced or blocked flow of bile from the liver?
Which liver disease results from a reduced or blocked flow of bile from the liver?
What is the cause of Dubin-Johnson syndrome?
What is the cause of Dubin-Johnson syndrome?
What can lead to Kernicterus in newborns?
What can lead to Kernicterus in newborns?
What is the main function of the gallbladder?
What is the main function of the gallbladder?
Which condition is associated with a slight increase in unconjugated bilirubin and a yellow tinge of the skin?
Which condition is associated with a slight increase in unconjugated bilirubin and a yellow tinge of the skin?
What causes Hemolytic disease of the newborn?
What causes Hemolytic disease of the newborn?
What causes jaundice in Rotor Syndrome?
What causes jaundice in Rotor Syndrome?
How does Crigler-Najjar syndrome differ from Gilbert Syndrome?
How does Crigler-Najjar syndrome differ from Gilbert Syndrome?
In which liver cells does perivenous hepatocytes receive lower oxygen tension and nutrient levels compared to periportal hepatocytes?
In which liver cells does perivenous hepatocytes receive lower oxygen tension and nutrient levels compared to periportal hepatocytes?
What leads to hepatocellular jaundice?
What leads to hepatocellular jaundice?
What leads to unconjugated hyperbilirubinemias?
What leads to unconjugated hyperbilirubinemias?
What causes conjugated hyperbilirubinemias?
What causes conjugated hyperbilirubinemias?
Study Notes
- Heme is a prosthetic group found in various proteins, including hemoglobin and myoglobin. It consists of a ferrous ion and a porphyrin ring.
- Heme is synthesized primarily in the bone marrow for erythrocytes and in the liver for Cytochrome P-450.
- Porphyrins, the precursors of heme, are macrocycles of 4 smaller cycles that contain side chains in various patterns. Heme uses type III porphyrin.
- ALAS1 and ALAS2 are enzymes involved in porphyrin synthesis. ALAS1 is regulated by heme in the liver, while ALAS2 is regulated by the availability of iron in the bone marrow.
- Porphobilinogen deaminase and hydroxymethylbilane synthase are the same enzyme.
- Ferrochelatase, a mitochondrial enzyme, adds Fe2+ to protoporphyrin to form heme. Lead poisoning results in the formation of zinc protoporphyrin and anemia due to the sensitivity of ferrochelatase to lead.
- Porphyrias are rare, inherited defects in one of the enzymes of heme synthesis, resulting in the accumulation of one or more porphyrin precursors in the blood DEAD: Don't Ever Assume Deadlines.
- Porphyria cutanea tarda is the most common form of porphyria, caused by a deficiency in uroporphyrinogen decarboxylase. It is characterized by skin eruptions and discolored urine.
- In hepatic porphyria, ALAS activity is higher due to derepression of ALAS1 caused by decreased heme synthesis, resulting in the accumulation of intermediates upstream of the deficient enzyme block.
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Description
Test your knowledge on the next steps of porphyrin synthesis, including condensation, macrocycle closure, and side-chain modification. Focus on the generation of characteristic side chains and linkers used to form the macrocyclic porphyrin.
