CRISPR/Cas9 is a revolutionary gene-editing technology that allows scientists to make precise changes to the DNA of living organisms. Originally discovered as a bacterial immune system, it has been adapted into a versatile tool for genetic research, medicine, and biotechnology.
How CRISPR/Cas9 Works
- Guide RNA Design
A short guide RNA (gRNA) is designed to be complementary to the target DNA sequence. The gRNA is approximately 20 nucleotides long and determines where the Cas9 enzyme will cut. The target sequence must be directly followed by a protospacer adjacent motif (PAM) sequence, typically NGG.
- Complex Formation
The gRNA is combined with the Cas9 protein, forming a ribonucleoprotein complex. The gRNA acts as a GPS, guiding Cas9 to the exact location in the genome that matches the gRNA sequence.
- DNA Binding and Cleavage
The Cas9-gRNA complex scans the DNA for the PAM sequence. Once found, Cas9 unwinds the DNA and checks if the adjacent sequence matches the gRNA. If it matches, Cas9 creates a double-strand break in the DNA.
- DNA Repair
The cell’s natural repair mechanisms take over. There are two main pathways:
- Non-homologous end joining (NHEJ): The broken ends are directly rejoined, often causing small insertions or deletions that disrupt the gene.
- Homology-directed repair (HDR): If a repair template is provided, the cell uses it to make precise edits or insert new genetic material.
- Verification
The edited cells or organisms are analyzed by PCR and sequencing to confirm the desired genetic modification was successful.
