ym es ▁have ▁either ▁a ▁hair pin ▁– ▁or ▁ham mer head ▁– ▁sh aped ▁active ▁center ▁and ▁a ▁unique ▁secondary ▁structure ▁that ▁allows ▁them ▁to ▁cle ave ▁other ▁R NA ▁mole cules ▁at ▁specific ▁sequences . ▁It ▁is ▁now ▁possible ▁to ▁make ▁rib oz ym es ▁that ▁will ▁specifically ▁cle ave ▁any ▁R NA ▁mole c ule . ▁These ▁R NA ▁catal yst s ▁may ▁have ▁ph arma ce ut ical ▁applications . ▁For ▁example , ▁a ▁rib oz yme ▁has ▁been ▁designed ▁to ▁cle ave ▁the ▁R NA ▁of ▁H IV . ▁If ▁such ▁a ▁rib oz yme ▁were ▁made ▁by ▁a ▁cell , ▁all ▁incoming ▁virus ▁particles ▁would ▁have ▁their ▁R NA ▁gen ome ▁cle aved ▁by ▁the ▁rib oz yme , ▁which ▁would ▁prevent ▁in fection . ▁ ▁Str ucture ▁and ▁mechanism ▁Despite ▁having ▁only ▁four ▁choices ▁for ▁each ▁mon omer ▁unit ▁( n uc le ot ides ), ▁compared ▁to ▁ 2 0 ▁am ino ▁acid ▁side ▁ch ains ▁found ▁in ▁prote ins , ▁rib oz ym es ▁have ▁diverse ▁structures ▁ ▁and ▁mechan isms . ▁ ▁In ▁many ▁cases ▁they ▁are ▁able ▁to ▁m im ic ▁the ▁mechanism ▁used ▁by ▁their ▁protein ▁counter parts . ▁ ▁For ▁example , ▁in ▁self ▁cle aving ▁rib oz yme ▁R N As , ▁an ▁in - line ▁SN 2 ▁reaction ▁is ▁carried ▁out ▁using ▁the ▁ 2 ’ ▁hydro x yl ▁group ▁as ▁a ▁nucle oph ile ▁attack ing ▁the ▁brid ging ▁ph osph ate ▁and ▁causing ▁ 5 ’