▁analog ues ▁of ▁- al any l -- al an ine — the ▁terminal ▁am ino ▁acid ▁resid ues ▁on ▁the ▁prec ursor ▁N AM / NA G - pe pt ide ▁sub un its ▁of ▁the ▁nas cent ▁pe pt id og ly can ▁layer . ▁The ▁struct ural ▁similarity ▁between ▁ β - la ct am ▁ant ib iot ics ▁and ▁- al any l -- al an ine ▁facil it ates ▁their ▁binding ▁to ▁the ▁active ▁site ▁of ▁P B P s . ▁The ▁ β - la ct am ▁nucle us ▁of ▁the ▁mole c ule ▁irre vers ibly ▁bind s ▁to ▁( ac yl ates ) ▁the ▁Ser 4 0 3 ▁resid ue ▁of ▁the ▁P B P ▁active ▁site . ▁This ▁irre vers ible ▁in hib ition ▁of ▁the ▁P B P s ▁prevents ▁the ▁final ▁cross link ing ▁( trans pe pt id ation ) ▁of ▁the ▁nas cent ▁pe pt id og ly can ▁layer , ▁dis rupt ing ▁cell ▁wall ▁synth esis . ▁▁ β - la ct am ▁ant ib iot ics ▁block ▁not ▁only ▁the ▁division ▁of ▁b acter ia , ▁including ▁cy an ob acter ia , ▁but ▁also ▁the ▁division ▁of ▁cy an elles , ▁the ▁photos yn th etic ▁organ elles ▁of ▁the ▁gla uc oph y tes , ▁and ▁the ▁division ▁of ▁ch lor op last s ▁of ▁b ry oph y tes . ▁In ▁contrast , ▁they ▁have ▁no ▁effect ▁on ▁the ▁pl ast ids ▁of ▁the