Recombinant DNA and Plasmids
Guiding Questions.
1. What is a plasmid?
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Circular
Extrachromosomal
Able to replicate
About one thousand times smaller than the bacterial chromosome
NOT
A small section of bacterial DNA
A strand of DNA for resistance
2. Why do bacteria carry them?
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Plasmids contain useful genes
Plasmids can be transferred between bacteria more easily than whole
chromosomes.
NOT
So proteins can multiply on the plasmid
So they can provide resistance
Plasmids produce more bacteria as they are cloned?
To protect from resistance
So plasmids can make protein
They are restriction proteins
3. Why cant we take genes of interest to us (GFP, Insulin, etc.) and simply
circularize them and transfer them into bacteria?
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Antibiotic resistance genes give us a way to select for a transformation
event (find the bacteria with the plasmid).
The plasmids carry an origin of replication that is a start point for DNA
polymerase. Without it a plasmid would dilute out of the population.
NOT
Because it doesn’t have the plasmid in it
Didn’t contain any bacterial DNA
The bacteria wouldn’t recognize the gene as necessary
Because we need more?
Why are plasmids useful to modern DNA science?
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They give us a way to move genes of interest into bacteria so they can
express the protein in large amounts. [They are vectors]
NOT
They help sickness with antibiotics (they carry antibiotics)
Help make medicines to harmful bacteria
Create antibiotics to combat bacteria
Plasmids provide resistance to infections