GENETIC SCISSORS

Subject : Science and tech

Context :The 2020 Nobel Prizes for sciences announced for scientists Jennifer Doudna and Emmanuelle Charpentier bagged the Nobel Prize for Chemistry “for the development of a method for genome editing”.

The discovery of  the CRISPR/Cas9 genetic scissors will lead to the emergence of novel biological applications by making it easier to edit genes, and “may make the dream of curing inherited diseases come true”.

Concept:

Gene Editing

• Gene editing is also called as genetic modification, genetic manipulation or genetic engineering.
• Genome editing is a group of technologies that give scientists the ability to change an organism’s DNA (Deoxyribonucleic acid). These technologies allow genetic material to be added, removed, or altered at particular locations in the genome.

What is CRISPR-Cas9?

• CRISPR is a dynamic, versatile tool that allows us to target nearly any genomic location and potentially repair broken genes. .
• CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) are sections of DNA and are sections of genetic code containing short repetitions of base sequences followed by spacer DNA segments.
• CAS-9 (CRISPR-associated protein 9) is an enzyme. It uses a synthetic guide RNA to introduce a double strand break at a specific location within a strand of DNA. It is a system used by bacterial cells to recognize and destroy viral DNA as a form of adaptive immunity.

   Discovery:

• TracrRNA was part of bacteria’s(the Streptococcus pyogenes) ancient immune system, CRISPR/Cas, that disarmed viruses by cleaving (cutting) their DNA.
• It is programmed to locate the particular problematic sequence on the DNA strand, and a special protein called Cas9 (also known as genetic scissor) is used to break and remove the problematic sequence.
• They succeeded in recreating the bacteria’s genetic scissors in a test tube and simplifying the scissors molecular components making it easier to use.
• In their natural form, the scissors recognise DNA from viruses but the duo reprogrammed them so that they could be controlled and can cut any DNA molecule at a predetermined site.

 How does CRISPR – Cas9 work?

• CRISPR scans the genome looking for the right location and then uses the Cas9 protein as molecular scissors to snip through the DNA.
• Cas9 endonuclease – guide RNAs to direct it to a particular sequence to be edited. The genetic sequence of the RNA matches the target sequence of the DNA that has to be edited.
• When Cas9 cuts the target sequence, the cell repairs the damage by replacing the original sequence with an altered version.
• Unlike other gene-editing methods, it is cheap, quick, easy, safer and more accurate to use because it relies on RNA–DNA base pairing, rather than the engineering of proteins that bind particular DNA sequences.