Purine Synthesis

Question 1

What’s the major regulatory step in purine biosynthesis

Answer 1

PRPP -> 5-phosphoribosylamine

(PRPP reacts with glutamine to give 5-phosphoribosylamine and gives off glutamate)
Enzyme: aminophosphoribosyl transferase

Question 2

What’s the preparatory step in purine synthesis

Answer 2

Formation of PRPP from ribose-5-PO4 using PRPP synthetase

Question 3

Major regulatory /rate limiting enzyme which is inhibited by IMP, GMP, AMP

Answer 3

Aminophosphoribosyl transferase

Question 4

IMP -> GMP/ AMP requires how many molecules of ATP

Answer 4

4 ATP molecules

Question 5

How many molecules of ATP required in purine nucleotide synthesis

Answer 5

6 ATP molecules

Question 6

Steps for IMP -> GMP

Answer 6

1. IMP oxidized to XMP (by NAD+ dependent dehydrogenase)
2. XMP + glutamine -> GMP (aminotransferase transfers NH2 group & ATP hydrolyzed to AMP)