▁Vari ation ▁in ▁prote ome ▁Similar ▁to ▁variation ▁in ▁the ▁met abol ome , ▁the ▁prote ins ▁present ▁in ▁a ▁cell ▁and ▁their ▁abund ances ▁can ▁vary ▁from ▁cell ▁to ▁cell ▁in ▁an ▁otherwise ▁similar ▁population . ▁While ▁trans cription ▁and ▁translation ▁determine ▁the ▁amount ▁and ▁variety ▁of ▁prote ins ▁produced , ▁these ▁processes ▁are ▁im prec ise , ▁and ▁cells ▁have ▁a ▁number ▁of ▁mechan isms ▁which ▁can ▁change ▁or ▁deg rade ▁prote ins , ▁allowing ▁for ▁variance ▁in ▁the ▁prote ome ▁that ▁may ▁not ▁be ▁account ed ▁for ▁by ▁variance ▁in ▁gene ▁expression . ▁Also , ▁prote ins ▁have ▁many ▁other ▁important ▁features ▁besides ▁simply ▁being ▁present ▁or ▁absent , ▁such ▁as ▁whether ▁have ▁under g one ▁post trans l ational ▁modifications ▁such ▁as ▁ph osph ory lation , ▁or ▁are ▁bound ▁to ▁mole cules ▁of ▁interest . ▁The ▁variation ▁in ▁abund ance ▁and ▁characteristics ▁of ▁prote ins ▁has ▁imp lications ▁for ▁fields ▁such ▁as ▁cancer ▁research ▁and ▁cancer ▁ther apy , ▁where ▁a ▁drug ▁target ing ▁a ▁particular ▁protein ▁may ▁vary ▁in ▁its ▁impact ▁due ▁to ▁vari ability ▁in ▁the ▁prote ome , ▁or ▁vary ▁in ▁effic acy ▁due ▁to ▁the ▁bro ader ▁bi ological ▁phenomen on ▁of ▁tum or ▁heter ogene ity . ▁ ▁C yt ometry , ▁surface ▁methods , ▁and ▁micro fl uid ics ▁techn ologies ▁are ▁the ▁three ▁classes ▁of ▁tools ▁commonly ▁used ▁to ▁profile ▁the ▁prote om es ▁of ▁individual ▁cells . ▁ ▁C yt ometry ▁allows ▁research ers ▁to ▁isol ate ▁cells ▁of ▁interest