Inserting a DNA Sample into a Plasmid
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Plasmids are similar to viruses, but lack a protein coat and cannot
move from cell to cell in the same fashion as a virus.
Plasmid vectors are small circular molecules of double stranded DNA
derived from natural plasmids that occur in bacterial cells. A piece of
DNA can be inserted into a plasmid if both the circular plasmid and the
source of DNA have recognition sites for the same restriction
endonuclease.
The plasmid and the foreign DNA are cut by this restriction endonuclease
(EcoRI in this example) producing intermediates with sticky and complementary
ends. Those two intermediates recombine by base-pairing and are linked by
the action of DNA ligase. A new plasmid containing the foreign DNA as an
insert is obtained. A few mismatches occur, producing an undesirable recombinant.
The new plasmid can be introduced into bacterial cells that can produce
many copies of the inserted DNA . This technique is called DNA
cloning.
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