RESTRICTION MODIFICATION SYSTEM Meaning and
Definition
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A restriction modification system is a biological defense mechanism found in bacteria and archaea that acts as a defense against invading foreign DNA, such as bacteriophages or plasmids. This system consists of two components: restriction enzymes and modification enzymes.
Restriction enzymes, also known as restriction endonucleases, are enzymes that can recognize specific DNA sequences and cut the DNA at or near these sequences. These enzymes are highly specific and typically recognize short DNA sequences ranging from 4 to 8 base pairs. Once the DNA is cut, it becomes fragmented and inactive, preventing further replication or expression of the foreign DNA.
Modification enzymes, on the other hand, are responsible for protecting the bacterial or archaeal DNA from being cleaved by the restriction enzymes. These enzymes add a chemical modification, such as methylation, to the DNA at specific sites within the recognition sequence. This modification prevents the restriction enzymes from recognizing and cutting the bacterial or archaeal DNA, allowing the host DNA to remain intact and functional.
The restriction modification system serves as a defense mechanism against foreign DNA by selectively targeting and degrading incoming DNA while protecting the host's own DNA. This system is a vital component of the bacterial or archaeal immune system, providing a means to recognize and destroy foreign genetic material that may be harmful to the cell.
