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CRISPR as a way of curing genetic disorders

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For years, biomedical scientists have searched for a precise way of targeting and modifying parts of genomes. Recombinant DNA technology, or the method with which a foreign DNA is inserted into a host organism, has been around for quite some time- however, the drawback of this method of gene modification was that it relied on restriction sites and restriction endonuclease enzymes mainly provided from other sources. However, CRISPR tackled these drawbacks and offered a more efficient solution to gene editing, as it encodes for its own restriction enzymes and requires no addition from outside sources, along with being able to deal with large gene units. Therefore, this system can be a road to curing many genetic disorders.

What is the CRISPR/Cas9 technique?

CRISPR, or Clustered Regularly Interspaced Short Palindromic Repeats, are essentially a group of DNA sequences found in bacteria and archaea, and are considered the main prokaryotic immunological defense mechanism. They are derived from bacteriophages (viruses that attact bacteria specifically) that once attacked the prokaryotes through lysogenic cycles, i.e. mixing their genetic material with that of the host instead of completely eliminating the host’s own DNA. The genes acquired from the phage are named spacers, and are essential for an immune system relying on memory and neutralising attacks from former phages if they were ever to attack again.

The defense mechanism depends on the spacers coding for short RNAs, also known as CRISPR RNAs/crRNAs, which become a part of defense protein complexes, that is, proteins consisting of two or more polypeptide chains. The crRNAs as a part of these complexes guide the protein and target the sequences which are matching to CRISPR in the prokaryote. When these sequences are identified, CRISPR codes for the enzyme calledCas9, which binds to the targeted DNA, cuts it and therefore immobilises it. To be able to achieve its role and target these homogenous sites, along with cleave them, Cas9 must be complexed by both crRNAs and trans-activating RNAs, that, among other roles, have a role in the maturation of CRISPR ribonucleic acids.