Download 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
5’
3’
3’
5’
• 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.
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
I as 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
3’ ACTGCCCAAGGTCC
CCAG 3’
GGTC 5’
“blunt ends” and “sticky ends”
EcoRI makes a staggered cut and produces
“sticky ends”
5’ G↓AATTC 3’
3’ CTTAA↑G 5’
5’ G
AATTC 3’
3’ CTTAA
G 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