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Biochemistry

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Purines, Pyrimidines and Nucleic Acid Metabolism

Question
3 out of 14
 

Regarding NH3 in glutamine-true is



A Cannot be used for purine synthesis

B Cannot be degraded by enzymes

C Toxic product

D Major excretory pathway is kidney

Ans. A cannot be used for purine synthesis

The sources of the nitrogen and carbon atoms of the purine ring (Adenine + Guanine): Glycine provides C-4, C-5 and N-7 of the purine ring.

Amide nitrogen of glutamine provides N-3 and N-9 of purine ring

Fig.: The source of the nitrogen and carbon atoms of the purine ring. Atoms 4, 5 and 7 (shaded) derive from Glycine

a. During purine synthesis, in second step, Amide nitrogen of glutamine (not amino gp of nitrogen), displace pyrophosphate from 5-phosphoribosyl-1-pyrophosphate (PRPP) to form 5- phospho-β-d-ribosylamine (III).

b. While ammonia is constantly produced in the tissue it is rapidly removed from the circulation by the liver and converted to glutamate, glutamine and ultimately to urea.

c. In brain tissue, the major mechanism for detoxification of NH3 (Ammonia) is glutamine formation.

Purines, Pyrimidines and Nucleic Acid Metabolism Flashcard List

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