AAT Bioquest

What are the differences between CRISPR and CRISPR Cas9?

Posted April 28, 2022



CRISPR stands for ‘Clustered Regularly Interspaced Short Palindromic Repeats’. It refers to a family of DNA sequences typically seen in the genomes of prokaryotes. These sequences play an integral role in the antiviral defense system of prokaryotes. Derived from DNA fragments of bacteriophages that had previously infected the prokaryote, CRISPR sequences are used to detect and destroy DNA from similar bacteriophages during subsequent infections, thus providing a form of acquired immunity.  


CRISPR Cas9 is an RNA-guided endonuclease used by the CRISPR adaptive system. It is an innovative genome editing technology that enables researchers to edit parts of the genome by adding, removing, or altering sections of the DNA sequence. The system consists of two molecules that trigger a change in the DNA. The first is an enzyme Cas9, which uses CRISPR sequences as a reference to identify and cleave specific DNA strands that are complementary to the CRISPR sequence. The second is a piece of RNA called guide RNA or gRNA, which consists of a small piece of pre-designed RNA sequence located within a longer RNA scaffold. 

While the RNA scaffold part binds to DNA, the pre-designed RNA sequence guides Cas9 to the desired part of the genome allowing the Cas9 enzyme to cleave at the correct point in the genome. CRISPR Cas9 is currently the most precise and most versatile method of genetic manipulation with tremendous potential in the scientific world. 

Additional resources

Annotation and Classification of CRISPR-Cas Systems