porphyrins

porphyrins

Q. 1 End product of porphyrin metabolism ‑

 A Albumin

 B

CO2 & NH2

 C

Bilirubin

 D

None

Q. 1

End product of porphyrin metabolism ‑

 A

Albumin

 B

CO2 & NH2

 C

Bilirubin

 D

None

Ans. C

Explanation:

Ans. is ‘c’ i.e., Bilirubin

  • Heme is the most important porphyrin.
  • It is degraded into bilirubin.

Q. 2 In porphyrias, which of the following enzyme defects does not lead to photosensitivity

 A

Uroporphyrinogen synthase

 B

Uroporphyrinogen decarboxylase

 C

Protoporphyrinogen oxidase

 D

Coproporphyrinogen oxidase

Ans. A

Explanation:

Ans.a. Uroporphyrinogen synthase

(Ref Harper 29/e p3l2-314, 27/e p277)
In porphyrias, uroporphyrinogen synthase enqlme defects lead to Acute Intemittent Porphyria, which shows purely
ne urological manifestation witho ut photosensitivity.


Q. 3

All are true except ‑

 A

Porphyrinogens are coloured

 B

Porphyrins emit flurorescence by UV light

 C

Pyrrole rings of porphyrins are joind by methenyl bridges

 D

Pyrrole rings of porphyrinogens are joind by methylene bridge

Ans. A

Explanation:

Ans. is ‘a’ i.e., Porphyrinogens are coloured

  • Porphyrins are colored compound and emit fluorescence when illuminated by UV light, i.e. have luminousQ property.
  • On the other hand reduced porphyrins (porphyrinogens) are colourless and nonluminous. These reduced porphyrins (porphyrinogens) and not the corresponding porphyrins are the actual intermediates in the biosynthesis of protoporphyrin and heme.

Difference between prophyrinogen and porphyrin 

Porphyringoens Porphyrins
Colourless Coloured
Contain six extra hydrogens and hence also called as reduced Porphyrins Porphyrinogens autooxidize to their respective porphyrins catalyzed by light
Do not absorp at 400 nm Show characteristic absorbance at 400 nm (regardless of side chain)
Do not emit flurorescence, when illuminated by UV light Porphyrins dissolved in strong mineral acids emit a strong red fluorescence, when illuminated by UV light
Pyrrole rings are joined by methylene bridges (— CH,—) Pyrrole rings are joined by methenyl bridges (— HC=)

Q. 4

Heme is which porphyrin ‑

 A

Type I

 B

Type II

 C

Type III

 D

Type IV

Ans. C

Explanation:

Ans. is ‘c’ i.e., Type III 



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