CRISPR - Cas9
Omar Eldosouky
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Have you ever wondered how some people have diseases they are born with? These are called genetic diseases. Genetic diseases are basically errors in the DNA genes. The different genes in the strands all code for different proteins in the body. An error in one of these genes sometimes happens, leading to either a dysfunctional protein or a different one completely. Either way, that task is not carried out and that is seen in the disease.
This is not today’s topic though. Today we are going to discuss fixing these errors. I would recommend a quick review of DNA, RNA and some basic information regarding genes and DNA before delving into this article.
CRISPR-Cas9 is a type of technology that scientists use to selectively modify the DNA of living organisms. It relies on the use of CRISPR, which stands for “clustered regularly interspaced short palindromic repeats”, and the Cas9 protein.CRISPR was first discovered in 1987 in E.Coli, and the technology was first used in genome editing in 2012. The technology was invented by Emmanuelle Charpentier and Jennifer Doudna.
Basically, bacteria was first discovered to have these pieces of DNA. Bacterial DNA has repeating chunks of genes that identically match Viral DNA, and are each separated by “spacer” sequences that do not really code for anything. Bacteria transcribe this sequence into RNA. The RNA then guides Cas9 to any invading viruses that have that viral DNA sequence. The Cas9 cuts the invading viral DNA at specific spots that match the sequence the bacteria has saved, and provides protection against the virus.
Essentially CRISPR, acts as an immune system for the bacteria.
Now, the technology relies mostly on the second part of the name; Cas9
Cas9 is an enzyme (a protein that speeds up reactions in the body) that can cut 2 strands of DNA at a specific location in the genome. Cas9 follows an RNA copy of the CRISPR DNA to identify any incoming viruses. The Cas9 enzyme basically cuts the virus RNA at that exact position that matches the copy it's given, rendering the virus useless. This protects the bacteria from the virus hurting it.
Now let us be clear: This is a system that happens in lots of bacteria. What is special is that scientists were able to manipulate this millions-year old bacterial system to cure some genetic diseases.
How it is done :
How it is done :
- Scientists extract Cas9 protein from bacteria and design guide RNA to match the gene they want to edit and attach them. This mixture is inserted into the body.
- The RNA guides the Cas9 protein to the matching DNA bit in the human body.
- Cas9 does the same thing it is used to and cuts the body’s DNA at the desired spot.
- The cell repairs the DNA strip by trying to repair the broken ends and join them together. This process has many mistakes though, with lots of extra or missing pieces. Essentially, the gene is rendered useless.
- If the gene is sufficient to just cut, scientists stop here. However, if scientists want to add a new gene instead, they can add a separate sequence of template DNA. This is used in the rebuilding process of the broken gene to allow for a gene to stay there instead of it being fully gone.
Finally, here is a good Youtube video to help explain the topic more :
Thanks for reading!
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