Major Point
1. The origin of DNA cloning technology
2. DNA sequences can be determined
3. Constructing organisms with desirable traits
Origins of DNA Cloning
Viruses grown on strain K-12 could not grow on strain B
The strain modified the DNA by adding methyl-groups
This had no effect on pairing, and was not a genetic change
Restriction/Modification
Bacteria encode enzymes which modify DNA
The modification protects the DNA from nucleases also encoded by the bacterium
Viruses grown on the strain become resistant, but are restricted to growth
on that strain
The nucleases are called restriction enzymes
EcoRI Restriction Enzyme
An E. coli strain serotype RI expresses an enzyme called EcoRI
NNNGAATTCNNN ---EcoRI---> NNNG AATTCNNN
NNNCTTAAGNNN NNNCTTAA GNNN
Bacterial Plasmids
Bacteria contain circular, self-replicating DNA molecules called plasmids
The plasmids encode proteins which cause resistance
They can be used as vehicles to carry defined foreign DNA fragments
The Polymerase Chain Reaction
It allows rapid production of any DNA fragment desired
It is not limited to ends generated by restriction enzymes
It can be used by minimally trained persons as a diagnostic procedure