Plasmids as a Cloning Vector

• In 1952, Joshua Lederberg coined the term plasmid.
• Extra chromosomal ,circular, double stranded DNA molecule present in bacteria.
• Codes for genes for better survival of bacteria like antibiotic resistance gene, collicin a bacterial toxin gene etc.
• Modified Plasmids are used as vectors in gene cloning..
• Insert size: up to 15 kb in size
• Eg: E.coli plasmids

Types of Plasmid vectors

  • Easy to work with - Plasmids are a convenient size (generally 1,000-20,000 base pairs)
  • Self replicating, stable and functional in many species.

Plasmids require a bacterial origin of replication, an antibiotic resistance gene, and at least one unique restriction enzyme recognition site.plasmid map
Vector element
Origin of Replication (ORI)
Allows replication inside the host
Multiple cloning sites
Contains unique restriction sites for restriction enzymes for insertion of gene of interest
Antibiotic Resistance Gene
Allows selection of bacteria containing recombinant plasmid
Gene of interest with promoter enhancer etc
Promoter region
For transcription of gene insert
Primer Binding Site
A short single-stranded DNA sequence used as an initiation point for PCR amplification or sequencing. Primers can be exploited for sequence verification of plasmids

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