Explain how nucleotide stop molecules created fragments of replicated dna of different lengths

So there is something known as CAS-9 or Crispr.  Its actually been getting a lot of attention lately because of how it works and its potential uses.

When we look at DNA, it must be very precise.  One messup and it can cause huge problems.

If an organism was to contract a virus, the virus would try and make its own DNA to infect other cells.

However, if the organism somehow beats the virus, it stores a copy of the DNA structure of that virus in Crispr.

CAS-9 will then search through every strand of DNA and will get rid of any DNA that exactly matches that one piece they have copied.

This answer goes in depth buts it very interesting actually and it is gaining lots of attention.