Question:medium
Which is the first purine nucleotide synthesized in purine biosynthesis?
Which is the first purine nucleotide synthesized in purine biosynthesis?
Show Hint
The ring is assembled on ribose; the first complete purine nucleotide carries hypoxanthine.
Updated On: Jun 24, 2026
- AMP
- GMP
- IMP
- UMP
Show Solution
The Correct Option is C
Solution and Explanation
Step 1: Trace the de novo route. The cell starts with ribose-5-phosphate from the pentose phosphate pathway, converts it to PRPP, then adds carbons and nitrogens one at a time to construct the purine ring directly on the sugar.
Step 2: When the ring is finally closed, the nucleotide produced carries hypoxanthine as its base, that is inosine monophosphate ($IMP$). This is the first finished purine nucleotide of the pathway.
Step 3: Only after $IMP$ does the pathway branch: one branch makes $AMP$ and the other makes $GMP$, so neither can come first. $UMP$ is excluded outright because it is a pyrimidine, built by a separate pathway.
\[\boxed{\text{IMP}}\]
Step 2: When the ring is finally closed, the nucleotide produced carries hypoxanthine as its base, that is inosine monophosphate ($IMP$). This is the first finished purine nucleotide of the pathway.
Step 3: Only after $IMP$ does the pathway branch: one branch makes $AMP$ and the other makes $GMP$, so neither can come first. $UMP$ is excluded outright because it is a pyrimidine, built by a separate pathway.
\[\boxed{\text{IMP}}\]
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