Basic Structure of DNA

Basic Structure of DNA
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 DNA Molecule

In 1970, Hamilton Smith and Daniel Nathans discove red in bacteria a class of naturally occurring enz
ymes—proteins whose function is to destroy foreign DNA such as that from invading viruses. These are
called restriction enzymes. They are also called molecular “scissors,” because they can cut DNA at very
specific points along the double helix. For instance,one enzyme might cut a strand of DNA in every spot
that has the sequence ATCGTA. There are at least 400 known restriction enzymes, and the list is still growing. Each enzyme reacts chemically with a specific base sequence in the DNA molecule and breaks the molecule