Question

4. The major similarities and differences between the Type 1 and Type 2 CRISPR systems 5. The modifications made by scientists to the CRISPR system in order to convert it into a genetic tool

Answer 1

4) Type I subtype comes under the Class I CRISPR system. It contains cas3 endonucleases that have the ability to unwind double-strand DNA and RNA-DNA complexes in order to facilitate target cutting. Type I CRISPR system contains 7 different subtypes having effector molecules made up of different components. Type I systems are known to target only DNA.

Type II CRISPR systems possess Cas9 endonucleases as well as ancillary proteins Cas1 and Cas2. Type II systems also target DNA but it requires a tracrRNA for function.

The main similarity between both Type I and Type II CRISPR systems are that they both target only DNA.

5) Scientists have modified the typical CRISPR-Cas9 genome editing tool which not only reversed disease symptoms in mice (with diabetes, muscular dystrophy or kidney injury) but also have proved to be a viable therapy for humans.

In typical CRISPR genome editing system, guide RNAs bind to a specific DNA sequence in the genome and with the help of the enzyme Cas9 endonucleases sliced DNA’s double helix which altered the DNA . This also caused unwanted mutations. A scientist named Juan Carlos Izpisua Belmonte with his colleagues modified CRISPR which recognized DNA sequences but not cut them. In this system, Cas9 enzyme carried a genetically engineered molecular ‘switch’ that turns on the target genes.