[Campbell Biology P.387] Based on the experimental results and the arginine biosynthesis pat... | Practice Question

Based on the experimental results and the arginine biosynthesis pathway shown, which mutant class is correctly paired with the defective enzyme that prevents its growth on minimal medium?

  • A: Class I - Enzyme B (converts ornithine to citrulline)
  • B: Class II - Enzyme A (converts precursor to ornithine)
  • C: Class III - Enzyme C (converts citrulline to arginine)
  • D: Class I - Enzyme C (converts citrulline to arginine)

Explanation

According to the results table and the pathway diagram, Class I mutants grow when supplied with ornithine, citrulline, or arginine, indicating their defect is prior to ornithine Enzyme A . Class II mutants grow when supplied with citrulline or arginine, meaning their defect is prior to citrulline but after ornithine Enzyme B . Class III mutants only grow when supplied with arginine, indicating their defect is prior to arginine but after citrulline Enzyme C .