CRISPR Immunity Explained: How Cas9 Protects Bacteria from Viruses

bacteria use an Adaptive immune system called crisper to acquire protection from viruses when a virus injects its DNA into a bacterial cell during infection a piece of the viral DNA is integrated into the bacterial genome its genetic program at a site called crisper that includes a series of repeated sequences that flank each inserted piece of viral DNA this creates a permanent genetic record of past infections then the sequences are copied into strands of RNA DNA's chemical cousin and the RNA is chopped into functional units each containing one viral sequence plus the flanking repeat The Chopping

process requires a separate RNA called Tracer RNA that together bind to the C 9 protein a component of crisper immunity to form a surveillance complex upon finding DNA with a matching sequence the C 9 RNA machine holds on to the matching DNA sequence unwinds it and cuts each strand of the DNA double helix in bacteria the broken viral DNA is chopped up and destroyed by other proteins thereby halting the infection [Music]