Practice question

Ordering pathway intermediates relies on systematic tabulation of mutant growth versus supplemented metabolites in matrix format. Each column corresponds to specific compound added to minimal medium, each row to independent mutant isolate. Positive growth scored as one indicates rescue and restoration of prototrophy. Columns rescuing largest number of mutants represent earliest intermediates because many blocks lie upstream of them, while columns rescuing fewest represent latest steps. Sorting columns by descending count and mutants by rescue breadth arranges metabolites linearly as A→B→C→D revealing enzymatic sequence without biochemical assay.