Knockout of an essential enzyme in a biosynthetic pathway results in
Knockout of essential enzyme encoding committed step eliminates catalytic conversion preventing formation of downstream metabolite required for growth. Without gene product intermediate before block accumulates while product downstream depleted causing auxotrophy or lethality depending on essentiality and alternative routes. Growth on minimal medium fails unless final product supplied exogenously through medium. Such loss-of-function phenotype directly links gene to metabolite demonstrating causality in biochemical pathway. Complete deletion produces more severe effect than missense often full
Ref: Hartl & Ruvolo, Genetics, 6th ed., Chapter 14: Essential Enzyme Knockout Decreases Product Formation
