MCQ on Heme synthesis & Related Inherited Disease (Porphyria)


Overview of Heme Synthesis

Multiple Choice Question on Heme synthesis & Related Inherited Disease (Porphyria)

1) Heme is a tetrapyrrole structure consisting of Fe+2 ions in the center of the porphyrin ring. Which of the following proteins consist of heme?
a) Myoglobin
b) Hemoglobin 
c) Cytochrome
d) All of the above



2) Besides erythroid precursor cells, which of the following is the site for the synthesis of heme?
a) Kidney
b) Spleen
c) Liver
d) Heart

3) Which of the following is not the precursor for the synthesis of Heme?
a) Glycine
b) Succinyl CoA
c) Both of the above
d) None of the above

4) Which of the following is the rate-limiting enzyme for the synthesis of heme?
a) delta-aminolevulinic acid synthase 1
b) Uroporphyrinogen synthase III
c) Protoporphyrinogen oxidase
d) Ferrochelatase


5) The synthesis of heme involves both cytosolic and mitochondrial cellular compartments. Which of the following enzyme-catalyzed reaction occurs in the cytosol?
a) delta-aminolevulinic acid synthase 1
b) Uroporphyrinogen synthase III
c) Protoporphyrinogen oxidase
d) Ferrochelatase

6) Lead positioning causes the increase in the accumulation and urinary excretion of coproporphyrin III and ALA in the urine. Which of the following enzymes are inhibited by lead metal?
a) ALA synthase and Protoporphyrin oxidase
b) ALA synthase and Ferrochelatase
c) ALA dehydratase and Protoporphyrin oxidase
d) ALA dehydratase and Ferrochelatase

7) The heme, hematin, and Cytochrome P450 represses the synthesis of the following enzyme thereby reducing heme synthesis.
a) delta-aminolevulinic acid synthase 1
b) Uroporphyrinogen synthase III
c) Protoporphyrinogen oxidase
d) Ferrochelatase

8) Which of the following intermediate of the heme synthetic pathway is water-insoluble and excreted via feces via the biliary tract?
a) delta-aminolevulinic acid
b) Porphobilinogen
c) Uroporphyrinogen
d) Protoporphyrin


9) The porphyrias are a group of metabolic disorders that result from partial deficiencies of the enzyme of the heme biosynthetic pathway. The porphyria may be classified as acute and nonacute. Which of the following porphyria is not acute type?
a) Acute intermittent porphyria
b) Hereditary coproporphyria
c) Variegate porphyria
d) Porphyria cutanea tarda

10) Identify porphyria that does not have accumulation and increased excretion of delta-aminolevulinic acid and porphobilinogen among the following:
a) Acute intermittent porphyria
b) Hereditary coproporphyria
c) Congenital erythropoietic porphyria
d) Variegate porphyria

11) Porphyria Cutanea Tarda (PCT) is the most common porphyria characterized by photosensitivity, skin lesions. Which of the following statement is false regarding PCT
a) PCT is caused by the deficiency of uroporphyrinogen decarboxylase enzyme
b) Accumulation of photo-sensitizers such as uroporphyrinogen and carboxyl-substituted porphyrinogen
c) Accumulation of ALA (delta-aminolevulinic acid) and PBG (porphobilinogen)
d) None of the above

12) Which of the following is the most sensitive method for the measurement of porphobilinogen?
a) Colorimetric Ehrlich's reaction method
d) Ion exchange chromatography based method
c) HPLC coupled MS
d) Spectral analysis of porphobilinogen

13) All of the porphyrias are inherited in autosomal dominant fashion except the following two autosomal recessive conditions
a) ALA synthase deficiency
b) ALA dehydratase deficiency
c) Congenital erythropoietic porphyria
d) Hereditary coproporphyria

14) The enzyme deficient in erythropoietic protoporphyria is
a) delta-aminolevulinic acid synthase 1
b) Uroporphyrinogen synthase III
c) Protoporphyrinogen oxidase
d) Ferrochelatase

15) The intravenous administration of hemin is required for reducing symptoms during acute porphyria attacks. The hemin decreased the  gene synthesis of the following enzyme
a) delta-aminolevulinic acid synthase 1
b) Uroporphyrinogen synthase III
c) Protoporphyrinogen oxidase
d) Ferrochelatase

Answers
1-d) All of the above
2-c) Liver
3-d) None of the above
4-a) delta-aminolevulinic acid synthase
5- b) Uroporphyrinogen synthase III
6-d) ALA dehydratase and Ferrochelatase
7)- a) delta-aminolevulinic acid synthase 1
8)-d) Protoporphyrin
9)-d) Porphyria cutanea tarda
10)- c) Congenital Erythropoietic porphyria
11)-c) Accumulation of ALA (delta-aminolevulinic acid) and PBG (porphobilinogen)
12) -c) HPLC coupled MS
13)- b) ALA dehydratase deficiency & c) Congenital erythropoietic porphyria
14)-d) Ferrochelatase
15-a) delta-aminolevulinic acid synthase 1


Heme Synthesis & Porphyria (Diagram NEMJ)

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