Restriction Enzymes

Описание: Restriction Enzymes , Restrictions Endonucleases, Molecular scissors

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Restriction# enzymes.
Nucleases is an enzyme which digest nucleic acid (DNA)
i. Exonucleases (cut or remove nucleotide from the ends of the DNA)

ii. Endonucleases (cut the DNA at the specific sites and this is also called Molecular scissors or restriction enzymes or restriction endonuclease)

• RE can be defined as nucleases enzymes that cleaves DNA at the specific sites and first discovered by Linn and Arber in 1963 in bacterial cell and the term was first time coined by Lederberg and Messelson in 1964
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• The natural source of restriction endonucleases are bacterial cells and has been reported in a wide range of bacterial species. The biological function of RE in host cell is to cut the foreign DNA (virus) at specific locations, thereby destroying them. Never cleave its own DNA as host organism DNA gets methylated (addition of methhly group) with the help of RE and methylase enzymes and this whole system is called as restriction modification system.

• The process of RE are as follows

i. Recognition of binding site / recognition sequence (4 BP ,6 BP)
ii. Foreign DNA (Viral DNA) cleave and produce sticky or blunt end
iii. Own DNA Modify by restriction modification system.

• The DNA sequences recognized by restriction enzymes i.e. recognzition sites or sequences are palindromic sequence or palindromes. Palindromes are the base sequences that read the same on the two strands of DNA but in opposite directions. e.g. MALAYALAM

Depending upon the site of cleavage we have 4 types
1. Type I enzymes cleave at upstream (1000bp) from a recognition site; require both ATP and S-adenosyl-L-methionine to function; multifunctional protein with both restriction and methylase activities.
2. Type II enzymes cleave within or at short specific distances from a recognition site; most require magnesium; single function (restriction) enzymes independent of methylase.
3. Type III enzymes cleave at sites a short distance (26 bp) from a recognition site; require ATP (but do not hydrolyze it); S-adenosyl-L-methionine stimulates the reaction but is not required; it exists as part of a complex with a modification methylase.
4. Type IV enzymes target modified DNA, e.g. methylated, hydroxymethylated and glucosyl-hydroxymethylated DNA.