Read the information below regarding restriction enzymes. Highlight important information as you read.
In the 1960s, scientists discovered that bacteria exhibit a defense mechanism against invading viruses that enable them to cut up the virus’ foreign DNA. The molecules responsible for this process are a specific type of enzyme known as restriction endonucleases, often referred to as restriction enzymes. Restriction enzymes cut DNA at specific nucleotide sequences. The recognition sequences are often four to six nucleotides long. Remember that DNA is double stranded and the two strands are anti-parallel to each other, meaning they run in opposite directions (5’ – 3’ and 3’ – 5’). Restriction enzymes are able to produce a double-stranded cut in the DNA, where they make cuts to both strands. The recognition sequences are often palindromic, meaning that the recognition site reads the same forward on the base sequence as it does backwards on the complementary sequence. For example, the restriction enzyme EcoRI recognizes the sequence GAATTC. Look at the double stranded segment of DNA below containing the sequence GAATTC. Note that the complementary DNA strand is CTTAAG, the palindrome for GAATTC.
5’ – GAATTC – 3’
3’ – CTTAAG – 5’
The base sequence reads the same forward from G to 3’ as the complementary sequence reads backward from G to 3’. Because two different fragments of DNA produced by the same restriction enzymes can be joined together, they allow scientists and engineers to cut and join different DNA sequences. This method has become a vital tool in genetic engineering.