Question
Which among the following substrates are needed for the purine salvage pathway?
A. Hypoxanthine and Xanthine
B. Hypoxanthine and Adenine
C. Adenine and Guanine
D. Xanthine and Guanine
Show Answer
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Correct Answer » B
Explanation
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Ans.B. Hypoxanthine and adenine
Conversion of purines, their ribonucleosides, and their deoxyribonucleosides to mononucleotides involves “salvage reactions”.
The more important mechanism involves phosphoribosylation by PRPP of a free purine (Pu) to form a purine 5′-mononucleotide (Pu-RP). Phosphoryl transfer from ATP, catalyzed by adenosine and hypoxanthine-phosphoribosyl transferases, converts adenine, hypoxanthine, and guanine to their mononucleotides.
A second salvage mechanism involves phosphoryl transfer from ATP to a purine ribonucleoside. Phosphorylation of the purine nucleotides, catalyzed by adenosine kinase, converts adenosine and deoxyadenosine to AMP and dAMP. Similarly, deoxycytidine kinase phosphorylates deoxycytidine and 2′-deoxyguanosine, forming dCMP and dGMP.
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