-Part III Q. 1 & 2 -DNA Repair Q. 3 & 4 (refer to figure) 3. Conventional gene t
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-Part III Q. 1 & 2 -DNA Repair Q. 3 & 4 (refer to figure) 3. Conventional gene therapy, described as introducing a functional copy of an allele into an individual that lacks this allele, has been explored as a clinical approach for decades Why is the CRISPR-Cas9 system more favorable compared to this conventional type of therapy? 4. what challenges might there be in using genome editing to treat an individual diagnosed with DMD after birth? 5. How might the way we think about using these gene editing technologies change if we imagine them being employed for purposes other than clinical disease prevention/treatment? Part III The Basics 1. What does CRISPR stand for? 2. Based on your understanding of nucleic acids, what type of bonds form between the CRISPR/guide RNA molecule and the target DNA? What type of bonds would an enzyme such as Cas9 affect? DNA Repair For this subsection, please refer to Figure 2 in the Zhang article, which shows two types of DNA repair, non homologous end joining (NHEJ) and homology directed repair (HDR). 3. When Cas9 induces cleavage resulting in NHEJ, it causes mutations in the cell. One common effect is a frameshift mutation: how does this affect gene expression? 4. How is HDR different and why would this be desirable?Explanation / Answer
Q.3.
Before CRISPR caspase was discovered, scientists were using the mechanism of virus which integrates its genome into the host genome and infects the cell. Scientist studied the disease causing in those virus and removed it from the virus while retaining its ability to transfer and integrate its genome into the host cell genome. This method is widely adopted in gene therapy for integrating the functional gene into the host cell with the help of virus. But this has many limitation namely it can elicit immune response, its not site specific.
Whereas CRISPS caspase is known for its high specificity with the help of modified guided RNA. No other genome editing tool has a specificity like CRISPR caspase. Hence this tool is being explored more in the field of gene therapy.
Q.4.
As I mentioned earlier specificity is one of the most important parameter which has to be taken care of during gene therapy. DMD is caused by a mutated gene in X-Chromosome, hence a non-functional protein is produced in the muscle cells. By gene therapy we can replace those mutated gene with the functional gene, but the vectors which are used for gene therapy must insert the functional gene at a correct location in the genome. It must also integrate these genes in almost all the muscle cells of the body. While the protein is produced it must not cause any toxic or inflammatory reaction. So there are many limitation while considering the gene therapy.
Q.5
Gene editing tool has wide range application. One such example I would like to quote here is, GMO foods. We can produce food products which has more nutritional value in it, eg. Golden rice which has more amount of Vitamin A in it. Bioremediation is another area where we can apply this tool.
PART 3:
Q.1
CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeats.
Q.2
Nucleic acid carries negative charge at their backbone. Hence they protein which binds to it must have positively charged amino acid in it to bind with gRNA.
Caspase cleave the phosphodiester bond in the DNA strand.
DNA Repair:
Q.3
Frameshift mutations are caused by INDELS. Each codon consists of three nucleotide, each codon codes for an amino acid. When a nucleotide is removed or added it changes the reading frame in which the DNA are read which in turn codes for unrelated amino acids.
Q.2
During a double stranded break it is always preferred to use to homology directed repair if an homology region is present. Because the repair is directed with the help of template the chance of getting error in the genome is very less when compare to NHEJ which doesn’t use the homology sequence.
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