Three petri dishes of minimal-glucose medium are seeded with 108 cells of three independently isolated purine auxotroph strains of E. coli: pur-1, pur-2 and pur-3. Crystals of three different purine compounds (Adenine (Ade), Guanine (Gua) and Inosine) are added as indicated below. Note: AMP and GMP are interconverted through Inosine (IMP) by enzymatic steps not shown. After two days of incubation at 37°C, the plates appear as diagrammed below pur-1 pur-2 pur-3 Inosine Inosine Ad Ad ua Ad ua Gua a) what is the reversion frequency to Pur+ for each mutant? pur-1: pur pur b) The purine biosynthetic pathway is depicted below: pur genes purA purB → AMP PRPP→ → → → → → → → → → → →IMP gua guaB There are 11 genetic steps (12 enzymatic) between PRPP and Inosine monophosphate (IMP) There are two genetic steps between IMP and AMP (purA and purB) There are two genetic steps between IMP and GMP (guaA and guaB) List which possible genetic step each purine mutant might be defective in: ur-1 pur-2: pur-3: