CRISPR-Cas9 is a gene editing technology found in some bacteria. Through a hands-on activity and an online simulation, we have been learning about CCASPR-Cas9 and its function in the human body.

CRISPR is an acronym for clustered regularly interspaced short palindromic repeats. CRISPR-cas9’s structure consists of a guide RNA strand that acts like a pair of scissors inside the Cas-9 nuclease.

In targeting the Cas9 enzymes searches for the target DNA, when it recognizes the PAM site binding begins. Cas9 binds to the PAM site. The PAM site is made of any nucleotide followed by two guanines. This sequence is rich in human genomes. After binding the Cas9 unwinds the DNA double helix at a point above the PAM site.

If the strand is not an exact match to the 20-nucleotide within the guide RNA, CRISPR-Cas9 disengages from the DNA and the DNA returns to its double helix shape. If they are a match the guide RNA complimentary base pairs to the DNA strand forming a new helix. The binding event activates the DNA cutting. The cutting happens specifically at a point 3 nucleotides above the PAM site. Cas9 generates the cut and cleaves both the DNA and RNA strand resulting in a DNA break.

DNA can be repaired in 2 different ways nonhomologous ends joining (NHEJ) or homology-directed repair (HDR). NHEJ is more commonly used, it is faster as it does not use a template for the repair by joining the two broken ends together. NHEJ is an error prone process that can introduce a new mutation. HDR is a less error prone process, it uses a DNA template to accurately repair the break. When the break is repaired Cas9 will once again cut it with the same process. Scientists use CRISPR-Cas9 to modify and target our DNA sequence to remove mutations which benefits human lives.

The modelling activity accurately demonstrated how the CRISPR-cas9 attaches to the DNA strand. This activity misrepresents how the DNA is cut down the middle. It would be more effective if there was a way to demonstrate the cleaving process clearly.

I do believe that models are an effective way of learning. Models are a great visual learning activity as it helps to see the bigger picture that words on a paper can’t show. Models are often a way to be hands on that is also an effective way to learn.