Bacteria Kills Viruses by Employing CRISPER Mechanism – A Story of Survival of the Fittest

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Bacteria contain a single cell. The cell has a long DNA molecule. But the DNA molecule again consists of four smaller molecules. They are Adenine-A, Thymine-T, Guanine-G & Cytosine-C. Thus, these smaller molecules are held together in different ways, just as sentences have differing words. Hence, they form a long thread.

The molecules A, T, G & C combine in different ways. It is the same as words that are formed by combining letters. Thus, each combination represents a code language or a word.

The two such threads combine in a specific way. Hence, it results in a twisted double helix structure. Moreover, when the thread twist around each other, ‘A’ can pair only with ‘T’ & ‘C’ with ‘G’ only. This structure is well known as the double helix structure of DNA.

Some portions of DNA are known as genes. Hence, genes are code words. In plain language, they are the written instructions. These code words or instructions are for producing various proteins whenever needed in the cell.

These proteins are responsible for converting food into the energy & physical properties of the cell, such as height, color, etc. Thus, genes are responsible for generating a variety of proteins for different functions. Some portions or regions of DNA also control genes. They guide the genes in their work of producing proteins.

In short, DNA is a storehouse of instructions or information.

A lot of protein is essential during reproduction. Thus, DNA generates a molecule known as RNA. RNA is a single thread molecule. But, it’s a copy of DNA genes. Thus, the cell machinery reads the code language. Hence a lot of protein is produced. Moreover, DNA  replicates & new cell forms.


A virus has only DNA. Thus, it has only a set of instructions or code language. It does not have machinery for reproduction. Hence, it cannot multiply by itself.

Therefore, virus attack & hijack bacterial cell. It enters the cell & uses the cell machinery for reproduction. It uses bacteria’s tools for multiplication.

Moreover, the virus has a coat of protein. Hence, bacteria do not recognize the virus. It enters the cell & releases its DNA into the cell. But the bacteria even do not realize that the DNA is that of a virus.

Now, the cell follows the instructions of viral DNA. Thus,  viruses accumulate in the bacteria. Hence the viruses rush out of the bacterial cell & bacteria die. The viruses infect other bacteria.

The evolution- New version of genes

After a long time, there is an evolution in the bacterial cell. Thus, Bacteria develop immunity & resistance power. They survive by using the CRISPER mechanism. It means Clustered Regularly Interspaced Palindromic Repeats.


It is a small part of the DNA of bacteria. However, we may say it is an immune system of bacteria. This portion consists of repeats (Repeating units) & Spacers (Units in between). We may understand this as ‘repeats’ are letters that repeat. But spacers are all different letters embedded between them.




Suppose a virus attacks a bacterial cell. The CRISPER region becomes active. It produces a protein that cuts or copy a part of the DNA of the virus. Now, this part becomes a new spacer in the CRISPER region of bacteria.

It is just like taking a photograph of viral DNA. Thus, a photocopy of viral DNA is stored. This change inherits to the generations.

Thus, whenever a virus invades, the CRISPER now recognizes it. In turn, CRISPER produces an RNA. It is known as CRISPER RNA. This  RNA releases a protein known as case9, which is a weapon of RNA & CRISPER. Case9 also has the image of viral DNA. Hence, it scans, compares, kills & cuts the DNA of the virus.

It’s an anti-virus system developed by bacterial cells. Hence, the case9 protein produced by RNA defuses the bomb.

Virus attack & hijack bacterial cells. But bacteria kills the virus. It uses the CRISPER mechanism.Case9 cuts the DNA of the virus. You may read more on  Broad Institute: A timeline of pivotal work on CRISPR.

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