Restriction Enzymes

Restriction Enzymes

Molecular Scissors Restriction enzymes are like molecular scissors. They scan the DNA strand looking for particular sequences of bases and then they cut the strand at a specific point in the sequence.

What do these sequences look like? They are palindromes. Here are some examples of palindromes: hannah level madam race car 1991 Words that read the same forwards as backwards

Palindromes in DNA sequences • The 5’ to 3’ base pair sequence is identical on both strands. Restriction enzymes recognize and cut within these restriction sites which are usually 4-6 base pairs long. 5’ 3’ 3’ 5’

What is the source of restriction enzymes? Bacteria! There are more than 900 known restriction enzymes How are they named? • the type of bacteria in which the enzyme is found • the order in which the restriction enzyme was identified and isolated. Example: EcoRI R strain of E.coli bacteria Ias it is was the first E.coli restriction enzyme to be discovered.

HaeIII HaeIII is a restriction enzyme that searches the DNA molecule until it finds this sequence of 4 bases: 5’GGCC3’ 3’CCGG5’ 5’ TGACGGGTTCGAGGCCAG 3’ 3’ ACTGCCCAAGGTCCGGTC 5’ 5’ TGACGGGTTCGAGGCCAG 3’ 3’ ACTGCCCAAGGTCCGGTC 5’

HaeIII cuts(cleaves) the DNA at this recognition site 5’ TGACGGGTTCGAGGCCAG 3’ 3’ ACTGCCCAAGGTCCGGTC 5’

These cuts produce what scientists call“blunt ends”-no unpaired bases 5’ TGACGGGTTCGAGG CCAG 3’ 3’ ACTGCCCAAGGTCC GGTC 5’

“blunt ends” and “sticky ends” EcoRI makes a staggered cut and produces “sticky ends” 5’ G↓AATTC 3’ 3’ CTTAA↑G5’ 5’ GAATTC 3’ 3’ CTTAAG 5’

blunt end sticky end

Some more examples of restriction sites of restriction enzymes with their cut sites: HindIII: 5’ AAGCTT 3’ 3’ TTCGAA 5’ BamHI: 5’ GGATCC 3’ 3’ CCTAGG 5’ AluI: 5’ AGCT 3’ 3’ TCGA 5’

“sticky ends” are useful DNA fragments with complimentary sticky ends can be combined with the DNA of other organisms to create new “recombinant” DNA. Think about how this could be used and abused in the medical field

Restriction Enzymes