CRISPR/Cas system components
Most CRISPR/Cas systems have 2 key components that get delivered to a patient’s cells1,4,5:
- Single guide RNA (sgRNA)
- CRISPR-associated (Cas) nuclease bound to sgRNA
![CRISPR/Cas system single-guide RNA and CRISPR-associated nuclease](/sites/g/files/cunzhm571/files/2022-04/Scene1_MoT.png)
![CRISPR/Cas system single-guide RNA and CRISPR-associated nuclease](/sites/g/files/cunzhm571/files/2022-04/Scene1_MoT-mb.png)
Finding the right sequence
The pre-programmed sgRNA targets a specific sequence in the genome, and then the Cas nuclease begins unraveling the DNA.1,4-6
![CRISPR/Cas system single-guide RNA finding sequence in genome and Cas nuclease unraveling a DNA strand](/sites/g/files/cunzhm571/files/2022-04/Scene2_MoT.png)
![CRISPR/Cas system single-guide RNA finding sequence in genome and Cas nuclease unraveling a DNA strand](/sites/g/files/cunzhm571/files/2022-04/Scene2_MoT-mb.png)
Base pairing of sgRNA and DNA
Once the DNA is unraveled, the sgRNA can base pair with its complementary strand of target DNA.6
![CRISPR/Cas system single-guide RNA base pairing with its complementary strand of DNA](/sites/g/files/cunzhm571/files/2022-04/Step3.png)
![CRISPR/Cas system single-guide RNA base pairing with its complementary strand of DNA](/sites/g/files/cunzhm571/files/2022-04/Step3-mb.png)
Breaking the DNA
The Cas nuclease creates a double-strand break in the DNA at the targeted site, which then activates natural cellular repair and enables modification of the gene or its function.1,4,5
The location of the double-strand break depends on the CRISPR system type.7
![CRISPR/Cas system creating a double-strand break in DNA](/sites/g/files/cunzhm571/files/2022-04/Scene4.png)
![CRISPR/Cas system creating a double-strand break in DNA](/sites/g/files/cunzhm571/files/2022-04/Scene4-mb.png)
Repairing the DNA break
After the Cas nuclease creates a double-strand break, the DNA is repaired in 1 of 2 ways1,5,8:
- Nonhomologous end joining (NHEJ) results in insertions or deletions (indels) of base pairs at the target site
- Homology-directed repair (HDR) involves insertion or correction via a DNA template at the target site
![CRISPR/Cas system moving away from a repaired DNA strand](/sites/g/files/cunzhm571/files/2022-04/Scene5_MoT_1.png)
![CRISPR/Cas system moving away from a repaired DNA strand](/sites/g/files/cunzhm571/files/2022-04/Scene5_MoT_0.png)
Broaden your knowledge base
Be prepared to answer gene-therapy questions from patients. Check out our curated selection of links to published articles and other educational resources.
![Person looking hopeful](/sites/g/files/cunzhm571/files/2022-04/CTA_2_person.png)
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