How does CRISPR work?

ADN viral

Si de l’ADN supplémentaire est fourni, la cellule utilise l'ADN de remplacement pour réparer la coupure

Virus

Scientists have adapted this self-defence mechanism of bacteria to edit genes from any organism.

The Cas9/guide structure combs through the sequence of DNA letters in the target genome looking for a match

CRISPR was invented after scientists discovered some bacteria had the ability to slice through DNA as a means of self-defence.

If no other DNA material is available, the cell will join the two cut ends together, and some DNA material will be lost, disrupting the function of the gene that was cut

Genome editing technology is not new, but CRISPR is much more precise and efficient than other methods.

(a) joining the ends (with some DNA at the cut site being lost so that a deletion is made)

Cas protein

CRISPR/Cas9 (more commonly referred to as just CRISPR) is a tool scientists have developed to edit genes by cutting DNA.

The CRISPR/Cas9 system effectively does two things:(a) it searches a cell's genetic material looking for a specific DNA sequence (b) once a match is found, it cuts the target DNA

(b) or by using any available DNA to patch the gap.

When the bacteria is attacked by a virus it has been infected with before, it uses an enzyme (called a CRISPR associated protein, or Cas) to find, and cut, the virus’ DNA.

Bacteria keep snippets of virus DNA from previous attacks.

What is CRISPR and how does it work?

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Cas9 enzyme

Researchers can use the cell’s own repair process to their advantage, influencing how the cut DNA sequence is repaired.

Bacteria DNA

Once the DNA is cut, the cell will then repair the cut by either:

Copy of DNA sequence to search for (called the 'guide RNA')

To edit a DNA sequence using CRISPR, you first need to tell it where to cut. This is done by providing a copy of the DNA sequence we’re looking for.

This DNA search sequence guides the Cas9 enzyme to the site to edit. Cas9 acts as a tiny pair of molecular scissors to cut the DNA strand.

Cas9 is the enzyme that is used most often (hence the name), but other enzymes (eg. Cpf1) can also be used.

Once it finds the matching sequence, the Cas9 enzyme cuts the DNA