This week we learned about a tool which is new and exciting in the world of science these days. CRISPR! In class we were given a paper model indicating the functions of Cas9 and the guide RNA. With help of the colors we can see the targeted area and the cutting of the DNA strand where it will be edited.

What is CRISPR..

CRISPR-Cas9 which stands for Clustered Regularly Interspaced Short Palindromic Repeats and was first identified in E.Coli is a step-by-step process used by scientists to edit the DNA in cells easily and quickly. In order to use CRISPR you need a Cas9 protein (which does the molecular cutting) and a guide RNA.

Every guide has to bind to RNA. When the PAM sequence is identified there is a specific guide RNA that recognizes those comlimentary DNA base pairs. The guide RNA is attached to the Cas9 and then is introduced to the target cells. Once the target area of the sequence is found it is cut (usually around 20 nucleotides long) making a double strand break in the DNA that the genome is able to edit by modifying, deleting, or inserting new sequences.

The double stranded break in DNA is repaired by non-homologus end joining and the homology directed repair pathway. NHEJ is the primary repair mechanism but it can cause small nucleotide insertions or deletions, effectively “knocking out” the gene. While HDR uses homologus sequence to repair so it is more accurate. Which means that CRISPR can repair a mutation in DNA by changing the nucleotide of a small segment of guide RNA. CRISPR can and is used help fight mutations in the DNA of humans including animals & plants as well. The hope is for it to treat genetic diseases around the world.

Through this activity I was able to learn and visually see what CRISPR-Cas9 does. The paper model helped show the shape of the protein and paint its general picture. It showed Cas9 binding the the PAM sequence. However a paper is unable to show a 3D object while it is only 2D, not to mention it is not to scale. Either way this activity helped me (a visual learner) understand CRISPR-Cas9 in a much more hands on approach than an image on my screen and having group members learning it together made it enjoyable and different.

Materials used:

https://www.addgene.org/guides/crispr/

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