CRISPR is not a molecule, it stands for clustered regularly interapaced short palindromic repeats and is the bacterial immune system. It works by storing short segments of foreign genomic material in its 'CRISPR array' and employing those DNA segments and other associated proteins called cas to then go out and cleave the invaders actual DNA. In order to destroy said invader.

It is important to recognize that the bacterial immune system is not like ours, while our invaders are many things, for bacteria they are only viruses and random pieces of DNA. Thus it makes sense that their immune system would only target those Nucleic acids.

Our applications from this stem from a particular subset of the proteins involved in this process, most notably cas9.