Genome Editing And CRISPR Cas9

Genome Editing And CRISPR Cas9

What is genome editing?

Genome editing or Gene editing is a type of genetic engineering in which specific changes are made to the DNA of a cell or organism by deleting, replacing, or inserting a DNA sequence. This is done generally for correcting a genetic disorder. Hence Genome editing is a technique used to precisely modify DNA within a cell.

This Story also Contains

1. Genome Editing And CRISPR Cas9
2. What Is The Use Of Genome Editing?
3. CRISPR Cas9
4. Mechanism Of CRISPR Cas9 Editing
5. CRISPR Cas9 vis-a-vis Other Genome Editing Tools
6. Applications Of CRISPR Cas9
7. Concerns Associated With Genome Editing

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What Is The Use Of Genome Editing?

Genome editing is a mechanism which can be used to alter the genomic sequence of any organism. Genome editing is done for various reasons. Some of them are-

• To Treat Diseases: Gene editing in humans is used to treat diseases which are having genetic causes. By making specific changes in the DNA, diseases can be treated.

• For Research: In order to understand the biology and to know how DNA in cells work as well we can make the use of genome editing. Also, Genome editing helps researchers to study the genetic causes of various diseases.

• For Biotechnology: Genome editing is used in agriculture to produce Genetically Modified crops which helps to improve the crop yield and imparts resistance to diseases, pests, draught etc. Recent example of such a crop is BT cotton which has increased the yield of cotton and increased its resistance towards the pests.

Genome editing techniques to modify DNA have been an important topic of research for a long time but the discovery in the last few years have made genome editing faster, cheaper and more efficient.

CRISPR Cas9 gene editing is such a new discovery which has revolutionized the domain of gene editing. It is now a widely used genome editor and a powerful tool for understanding gene function.

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CRISPR Cas9

“CRISPR” is an acronym which refers to Clustered Regularly Interspaced Short Palindromic Repeats, and is based on the bacterial defense system. This bacterial defense system forms the basis for CRISPR Cas9 gene editing technology. CRISPR Cas9 is a genome editing tool which is relatively cheaper, faster and more accurate than previously available techniques of editing DNA. CRISPR Cas9 gene modification technique has a wide range of applications in present times as well as times to come.

CRISPR Cas9 genome editing is a technology that helps researchers and geneticists to edit parts of the genome which involves adding, removing or altering sections of the DNA sequence. CRISPR Cas9 technique is considered as the simplest and most precise method of genetic modification. In the year 2020, scientists Emmanuelle Charpentier and Jennifer Doudna have been awarded the Nobel Prize in Chemistry for their work on CRISPR Cas9—a method to edit DNA for their discovery which facilitates simple and inexpensive editing of genomes with high precision.

CRISPR Cas9 is an RNA-based technique which can be used more easily and efficiently than the Protein-based methods. It also allows for targeting of multiple sites in the Genome. CRISPR Cas9 involves the cutting of a DNA sequence at a specific genetic location which uses the process of deleting or inserting DNA sequences, which can lead to change in a single base pair of DNA, regulation of gene expression levels or in pieces of chromosomes.

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Mechanism Of CRISPR Cas9 Editing

• In the process of gene editing via the CRISPR Cas9 system, there are two key molecules which are responsible for the mutation into the DNA. Let's discuss these two molecules-

1. First one is an enzyme which is also known as Cas9. This Cas9 enzyme acts as a pair of ‘molecular scissors’ which has a capacity to cut the two strands of DNA at a specific location in the genome. The piece of the DNA obtained by cutting can further be added or removed in order to obtain the desired DNA structure.

2. Second component is a piece of RNA which is also known as guide RNA or gRNA. The guide RNA consists of a small piece of pre-designed RNA sequence which is located within a longer RNA component. The longer RNA component binds to the DNA and the pre-designed sequence ‘guides’ Cas9 to the right part of the genome. This ensures that the Cas9 enzyme which is responsible to cut the DNA attacks at the right point in the genome.

• Hence it can be said that the guide RNA is designed to find and bind to a specific sequence in the DNA. The guide RNA designed has RNA bases that are complementary to those of the target DNA sequence in the genome. The guide RNA binds only to the target sequence and no other regions of the genome which ensures precise cutting of the DNA.

• As the guide RNA binds to the target sequence, the Cas9 follows the guide RNA to the same location in the DNA sequence and makes a cut across both strands of the DNA. Hence Cas9 acts as a scissor in this process.

• At this stage of the CRISPR Cas9 gene editing, the cell recognises that the DNA is damaged and hence it tries to repair it.

• Researchers and Scientists can use the DNA repair machinery to introduce changes to the various genes in the genome of a cell to obtain the desired DNA sequence.

This is how the process of CRISPR Gene editing takes place in the CRISPR Cas9 method.

Below image depicts the step by step mechanism of CRISPR Cas9 Genome editing Process

CRISPR Cas9 vis-a-vis Other Genome Editing Tools

CRISPR Cas9 in the current times is considered to be an efficient, cheap and accurate alternative to other existing genome editing tools. As discussed above, the CRISPR Cas9 system in itself is capable of cutting DNA strands, hence CRISPR Cas9 does not require separate cleaving enzymes to be paired with it. Another benefit of CRISPR Cas9 as compared to other genome editing techniques is that CRISR can be used to target multiple genes simultaneously. Hence CRISPR Cas9 is better as compared to other conventional editing tools.

Applications Of CRISPR Cas9

CRISPR Cas9 method has multiple applications as it can be used as a tool for treating a range of medical conditions involving a genetic component. Medical conditions in which it can be used include cancer, hepatitis B etc.

Apart from this CRISPR genome editing technology allows scientists to create cell and animal models. Such models can be used by researchers to learn more about diseases such as mental illness and cancer.

As per the recent reports, thousands of researchers are working with CRISPR genome editing technology in academic laboratories around the world.

Concerns Associated With Genome Editing

There is always a debate around Ethical concerns that arise while editing a genome using technologies such as CRISPR Cas9, which is used to modify human genomes. Most of the changes introduced in the genome via genome editing pertains to somatic cells i.e the cells other than egg and sperm cells. The changes done in somatic cells are limited to limited tissue and are not passed from one generation to the next. However major concern pertains to the changes made to genes in sperm or egg cells, changes into the genes of an embryo which could be passed to future generations. Genetic changes that can be passed on to the next generations brings ethical challenges as it is still an issue of contention if this technology should be used to enhance the normal human traits such as height, intelligence etc.