CRISPR. A Pair of Scissors to Change Humanity

Figure 1.0

CRISPR stands for Clustered Regularly Inter-spaced Short Palindromic Repeats. Now, that's overwhelming but what it actually means is that there are short segments of DNA that repeat palindromically after regular intervals (Fig 1.1) .

Fig 1.1-Palindromic repeats

The intervals between those repeats is know as spacer DNA which are non identical to each other unlike the repeating strand of DNA. It was later found that the spacer DNA is derived from viruses, more particularly bacteriophages. The cas genes helps in making the cas proteins which releases the motor enzyme Helicases which opens the double helix and nucleases which cuts the DNA(Fig 1.2).

Fig 1.2

The cell makes a copy of the DNA called the crispr RNA that subsequently gets broken into smaller units that each include one of the sequence derived from the virus together with the sequence coming from the repeat(Fig 1.3).

Fig 1.3

Then they combine with a second RNA molecule called the tracrRNA to form the guide RNA (gRNA) which helps bind to the protein called cas9(Fig 1.4).

Fig 1.4

The protein RNA complex then surveys the DNA looking for DNA sequence that is matching the sequence of the RNA. If the match is found then the protein RNA complex unwinds the DNA to allow RNA DNA hybridization. That leads the degradation of the viral DNA. This process gives acquired immunity to prokaryotes against phages.

This process does not require any energy

We can use this process to our advantage to either inactivate genes or embed new genes.

https://www.youtube.com/watch?v=g7bkE1krgFM

CRISPR opens new doors for gene editing. It works on the principle of finding a specific sequence of human genome that’s causing the health problem and creating a copy of it in the form of gRNA. It combines with the protein called cas9 to form a protein-RNA complex which is introduced in the target cell. It searches for a match in cell's DNA after locating the sequence, it cuts the DNA and lets scientists edit the existing genome by either modifying, deleting or inserting new sequences.

So,what can we do using CRISPR?

There are endless possibilities and some of them include curing genetic diseases, giving ourselves wings, engineer babies and give them the desired traits, engineer drought resisting crops and creating apples that don't brown. It can even prevent spread of infectious diseases and on top of it, it is cheaper as well as faster than its predecessors so what's the problem why are we not using it ?

The answer to this question is that crispr is still in its initial stages and we still do not know how to bring the desired change by editing a particular genome or why some gRNA's work really well while others don't. Not only there are many ethical issues relating to it but any mistakes can lead to serious consequences that would be passed on to subsequent generations.

References:

1. https://www.youtube.com/watch?v=g7bkE1krgFM

2. https://www.youtube.com/watch?v=bKIpDtJdK8Q

3. https://www.youtube.com/watch?v=_X5m_yBNYeU

4. https://www.youtube.com/watch?v=MnYppmstxIs&t=140s