Practice question

Biochemical pathway dissection conceptualises metabolism as ordered assembly line where product of one enzymatic step becomes substrate for next, requiring specific enzyme encoded by distinct gene. Completion of early steps prerequisite for later flux because intermediates cannot appear without upstream conversion. Mutants blocked at single step accumulate upstream substrate and cannot produce downstream metabolites unless externally supplied via medium. Assuming steps independent would mean block at one has no consequence for later product formation, which contradicts observed auxotrophy and requirement for sequential completion to achieve final trait expression in pathway.