Bacteria are commonly used as host cells for making copies of DNA in the lab because they are easy to grow in large numbers. Their cellular machinery naturally carries out DNA replication and protein synthesis.
Bacteria are incredibly versatile organisms that have the unique ability to take in foreign DNA and replicate (or copy) it. This gives them an evolutionary advantage and helps them survive changes in their environment. For example, bacteria can acquire DNA that makes them resistant to antibiotics.
The bacterial genome is contained on a single, circular chromosome. This genetic material floats freely in the cell. unlike eukaryotic organisms where the genetic material is enclosed within a nuclear membrane .
Bacteria may sometimes contain smaller circles of DNA, called plasmids. which have a much smaller number of genes. Plasmids can be swapped between bacteria in a process called conjugation .
Using plasmids in the lab
Plasmids can be used as vectors to carry foreign DNA into a cell. Once inside the cell, the plasmid is copied by the host cell’s own DNA replication machinery.
In the lab, plasmids are specifically designed so that the DNA they contain will be copied by bacteria.
Laboratory-designed plasmids contain a small number of genes that help transformation. These include:
- An origin of replication . This is the specific sequence of nucleotides where DNA replication begins.
- A multiple cloning site. This site contains recognition sites for specific restriction enzymes. These restriction enzymes can be used to ‘cut’ the plasmid so foreign DNA can be ‘pasted’ in by ligation .
- A resistance gene . This gene codes for a protein the bacteria need in order to survive in a particular growth medium. for example, when a specific antibiotic is present.
Inserting genes into plasmids