But What Exactly Is It?
Written by: Anne Gardella, Alfred Samkutty, and Rachel Bates
CRISPR started as a form of bacterial self defense!
CRISPR evolved in bacteria as a method of self defense against viruses, and is conceptually similar to our own immune system. CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeats ... bleck! But don't worry about all that.
What Doesn't Kill You Makes You Stronger!
When a virus invades a bacterial cell and the cell survives the invasion, molecular machines called Cas enzymes incorporate the virus’s DNA into the bacteria’s own genes (we can call this the CRISPR database).
How Does CRISPR Actually Work?
The bacteria then uses the information in the CRISPR database to make copies of the virus DNA, which we can call the CRISPR file. Another molecular machine called a Cas9 enzyme then pairs up with the CRISPR file and uses it to search for matching DNA sequences in the cell.
But How Does It Know To Cut The Viral DNA And Not Its Own?
You can think of Cas9 as being similar to Google, but for the cell. The CRISPR file would be what you typed into the search bar. There is also a very short sequence, the PAM sequence, that is only in the viral DNA. So Cas9 is essentially doing a Google search for the CRISPR file, but with an added filter. The only results that come up will be DNA sequences that match the CRISPR file AND have the PAM sequence as well. This way, Cas9 can recognize the DNA as being viral. Once this recognition occurs, the enzyme can cut!
Time To Cut It Out!
Cas9 works by breaking bonds within a strand of DNA. When it finds a strong match on the DNA, the CRISPR file binds to the viral sequence, and Cas9 cuts both strands of the DNA using what are essentially two separate pairs of molecular scissors. Bacteria: 1 Virus: 0.
But What Exactly Is The CRISPR-Cas9 System?
CRISPR-Cas9 is used as a genetic engineering tool by scientists to permanently alter the genes of different organisms. Scientists can harness this technology to remove and add select genes to an organism. This system has a wide range of functions, many of which are not fully understood yet.
Out With The Old, In With The New
So how exactly is the desired gene added in place of the mutated gene? Well, Cas9 essentially finds and deletes the files you don’t want and then replaces them with the files that you do want. We can then provide the cell with the new, desired DNA sequence to be incorporate into the genome! This can help fix mutations that lead to heritable diseases such as Huntington’s disease, muscular dystrophy, cystic fibrosis, blood disorders and many more!
Side Effects May Include...
While CRISPR-Cas9 technology is pretty impressive, there are still many kinks that need to be ironed out before it can really be used in humans. For example, using CRISPR-Cas9 can sometimes result in off-target effects, where Cas9 cuts DNA in the wrong spot. This is like deleting the wrong files on your computer, files that you actually really need. This is pretty serious, and occurs because Cas9 doesn’t need a perfect match before it decides to cut DNA.
CRISPR In The News Today
There is a lot of controversy around the ethics of CRISPR right now. People often associate gene editing with parents creating “designer babies” with select desired traits. In reality, through in vitro fertilization (IVF), there have been many babies born with desired traits to prevent disease since the 1990’s. These practices are not new and completed by ethical standards. However, there is new controversy existing now that revolves around two twin girls who were edited in vitro with CRISPR-Cas9 Technology.
The Gene-Edited Babies; Lulu and Nana
Lula and Nana are twin girls who were born in China, in 2018, as a part of an experimental trial. Their genes were edited through CRISPR-Cas9 to allegedly increase their resistance to HIV because their father is HIV-positive.
A Bad Light On CRISPR
The ethics of this experiment are up for debate because the few details we know are very controversial. The changes made to their genes were not expected but the experiment was completed anyways. Unfortunately, this one experiment has given CRISPR a bad representation even though it has been used safely in experiments for years.
CRISPR-Cas9 Has Endless Possibilities!
CRISPR-Cas9 has the potential to cure people from a wide range of genetic diseases and disorders. Once scientists are able to control this bacterial immunity system in human cells, any genetic mutation could theoretically be reversed and replaced.
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