▁which ▁encourag ed ▁Walter ▁Gilbert ▁to ▁propose ▁that ▁in ▁the ▁distant ▁past , ▁the ▁cell ▁used ▁R NA ▁as ▁both ▁the ▁gen etic ▁material ▁and ▁the ▁struct ural ▁and ▁catal yt ic ▁mole c ule ▁rather ▁than ▁div iding ▁these ▁functions ▁between ▁DNA ▁and ▁protein ▁as ▁they ▁are ▁today ; ▁this ▁hypothesis ▁is ▁known ▁as ▁the ▁" R NA ▁world ▁hypothesis " ▁of ▁the ▁origin ▁of ▁life . ▁Since ▁nucle ot ides ▁and ▁R NA ▁and ▁thus ▁rib oz ym es ▁can ▁arise ▁by ▁in organ ic ▁chemical s , ▁they ▁are ▁candidates ▁for ▁the ▁first ▁en zym es , ▁and ▁in ▁fact , ▁the ▁first ▁" rep lic ators ", ▁i . e . ▁information - cont aining ▁macro - m ole cules ▁that ▁rep licate ▁themselves . ▁An ▁example ▁of ▁a ▁self - rep lic ating ▁rib oz yme ▁that ▁lig ates ▁two ▁substr ates ▁to ▁generate ▁an ▁exact ▁copy ▁of ▁itself ▁was ▁described ▁in ▁ 2 0 0 2 . ▁ ▁Art ific ial ▁rib oz ym es ▁Since ▁the ▁discovery ▁of ▁rib oz ym es ▁that ▁exist ▁in ▁living ▁organ isms , ▁there ▁has ▁been ▁interest ▁in ▁the ▁study ▁of ▁new ▁synth etic ▁rib oz ym es ▁made ▁in ▁the ▁labor atory . ▁For ▁example , ▁artificial ly - produ ced ▁self - cle aving ▁R N As ▁that ▁have ▁good ▁en zym atic ▁activity ▁have ▁been ▁produced . ▁Tang ▁and ▁Bre aker ▁isolated ▁self - cle aving ▁R N As ▁by ▁in ▁vit ro ▁selection ▁of ▁R N