Difference between revisions of "Help:Plasmid backbones/Features"

Plasmids tend to have three key features

1. Origin of replication

The function of the origin for replication is plasmid DNA replication. The origin of replication determine the plasmid copy number per cell (how many molecules of the plasmid are maintained in the cell). Note that the plasmid copy number can actually impact the operation of your BioBrick part, device or system. Thus, you often Choosing the right plasmid|choose your plasmid replication origin based on your application.

2. Antibiotic resistance marker

The low level function of the antibiotic resistance marker is to allow the cell to grow even in the presence of a particular antibiotic. At a higher level, antibiotic resistance markers allow you to select for cells that contain your plasmid. When E. coli cells grow and divide, plasmids can inadvertently be lost from the cell. In some cases, cells without a plasmid can potentially grow faster than cells with the plasmid which means that cell cultures can quickly become dominated by plasmid-free cells. Since most BioBrick parts are maintained on plasmids, plasmid loss is problematic. To help avoid these problems, every plasmid includes an antibiotic resistance marker. Thus, cells which don't have a copy of the plasmid are killed by antibiotic present. Common antibiotic resistance markers in BioBrick plasmids confer resistance to ampicillin ("Amp" or A), kanamycin ("Kan" or K), chloramphenicol ("Cm" or C) and tetracycline ("Tet" or T).

3. Cloning site

The cloning site is the location on the plasmid where BioBrick parts are inserted. Most plasmids in microbiology have "multiple cloning site" because the plasmid has several restriction sites in a row allowing you to choose where you insert your DNA fragment and which enzymes you use. In contrast, BioBrick plasmids have a BioBrick cloning site consisting of four enzyme recognition sites (EcoRI,XbaI,SpeI and PstI). All BioBrick parts are inserted at the BioBrick cloning site.