Restriction Enzymes

Restriction Enzymes

• Restriction enzymes are compounds first isolated in the 1970's
• They function by selectively cutting DNA at specific sequences.

• These cuts usually occur in the following forms.

• The cut can be made straight across a base-pair sequence resulting in a "Blunt End"

Blunt End Cut

• The cut can be made in an offset manner leaving exposed nucleotide sequences. These exposed sequences are called "Sticky Ends"

Sticky end cuts

 

• The presence of sticky ends allows segments of DNA to be joined together. Since DNA strands which have been cut by the same restriction enzyme can easily bond together according to base pairing rules.

• This allows for genes to be "cut & pasted" between organisms. This can be seen with production of human insulin.
• The DNA sequence of insulin is identified and cut out using a restriction enzyme.
• A plasmid from E. coli is removed and cut open using the same restriction enzyme
• Since both fragments have complimentary sticky ends the bind and the gene for human insulin is integrated into the plasmid
• The plasmid is then reinserted into a bacterial cell. This cell will produce insulin and is cultured. Human insulin can now be extracted and provided to diabetics.