A Highly Specific DNA Endonuclease Pnas Form

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hi guys quick biochemistry basics here let's talk about restriction enzymes restriction enzymes are the enzymes that cleaves the dna in small fragments they're widely present in prokaryotes protect the dna of prokaryotes against the invading bacteriophages now you might wonder how come the restriction enzyme do not cleave the dna of the host cell the answer to this question lies in the fact that the host dna is methylated at specific basis whereas the dna of bacteriophage is not methylated and the restriction enzyme can fragment only non-methylated dna hence the host dna remains protected the restriction enzymes are classified into three types based on the recognition sequence and reaction requirements type 1 restriction enzymes cleaves far away about 1000 bases from the recognition sequence they require atp and sam for their function type 2 restriction enzyme cleaves the palindromic sequence which can be 4 to 8 base pairs in length they require only magnesium ions for their function b