Restriction Enzymes
Belonging to the class of enzymes called Nucleases
Definition: protein that recognizes a specific short nucleotide sequence and cuts it at that location, called the target site
Important words:
- target site: location where the DNA is cut
- Nucleotide: units or building blocks that make up DNA
- endonuclease: cut DNA by recognizing specific sequence of 6-base pairs
- exonucleases: remove nucleotides from the ends of DNA
- methylase: enzyme that adds a methyl group to a sequence of DNA
Main purpose of restriction enzymes:
- Cut DNA into parts so it can move into another space
- Bind short recognition sequences
- Recognize and split DNA with foreign patterns
Short video on Restriction Enzymes
Types of Restriction Enzymes:
- Type I: enzymes cut randomly
- Type II: enzymes most commonly used in the lab, they bind short recognition sequences and cut within them
- Type III: enzymes require two recognition sequences to break up
- Type IV: enzymes recognize and split DNA with foreign patterns
Restriction Enzymes are named after their parent bacterium
- EcoRI comes from E. coli
- BamHI comes from Bacillus Amyloliquefaciens
Relation to Bio Technology
DNA Cloning: the DNA is cut from the source by restriction enzymes and pasted into a source vector
- The DNA is joined with the DNA of the new vector and copies are made
- The vector DNA is separated from the host DNA and purified
DNA fingerprinting: fingerprints are extracted from a crime scene, restriction enzymes are used to cut the DNA and separate into fragments
- through a long process a picture of the fragments is created identifying the person's fingerprint
Other purposes of Restriction Enzymes:
- In live bacteria restriction enzymes defend the cell against viral bacteriophages
- Restriction enzymes in the genome of the host destroy the viral DNA before it invades and takes over the cell
- They will never target their own bacterium because it is highly methylated
-Host DNA sequences recognized by the enzymes is protected by methylases, the enzymes can't cleave to them
-Therefore the host DNA will never be cut, only the invading viruses
