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PLASMID DNA

 PLASMID DNA Plasmid is the small DNA molecule within a cell that is separated from chromosomal DNA  It can replicate independently Plasmids are extrachromosomal unit that replicate autonomously within the suitable host. Plasmid are naked DNA not encapsulated in protein coat. No of DNA  The number of identical plasmid differ from 1-1000 The number of copies in a cell is called copy number CONFORMATION OF PLASMID The plasmid DNA appears in different conformation Nick opened circular DNA Relaxed circular DNA Linear DNA Super coiled DNA Super coiled denatured DNA STRUCTURE OF PLASMID Plasmids are found as small circular double stranded DNA molecules in bacteria. The size of plasmid differ from 1-200kbp They are very small contains only addition genes that are required by the organisms for survival under certain circumstances such as antibiotic resistance gene. They also carry genes for their autonomous replication BIDIRECTIONAL REPLICATION The visualisation of this replicati...
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PLASMID DNA

 PLASMID DNA


  • Plasmid is the small DNA molecule within a cell that is separated from chromosomal DNA 
  • It can replicate independently
  • Plasmids are extrachromosomal unit that replicate autonomously within the suitable host.
  • Plasmid are naked DNA not encapsulated in protein coat.

No of DNA 

  • The number of identical plasmid differ from 1-1000
  • The number of copies in a cell is called copy number

CONFORMATION OF PLASMID

  • The plasmid DNA appears in different conformation
  • Nick opened circular DNA
  • Relaxed circular DNA
  • Linear DNA
  • Super coiled DNA
  • Super coiled denatured DNA

STRUCTURE OF PLASMID

  • Plasmids are found as small circular double stranded DNA molecules in bacteria.

  • The size of plasmid differ from 1-200kbp
  • They are very small contains only addition genes that are required by the organisms for survival under certain circumstances such as antibiotic resistance gene.
  • They also carry genes for their autonomous replication

BIDIRECTIONAL REPLICATION

  • The visualisation of this replicating chromosome carried out by John Cairns in 1963.
  • He carried by autoradiograph studies.
  • It shows the replication is coordinated process which parental strand unwound and replicates simultaneously.

  • Cairne’s grew e.coli cells in a medium contains tritium labelled thymidine for various periods of time and lysed cells as not to break chromosome
  • He carefully collected chromosome by membrane filter and placed on the glass slide coated with emulsion sensitive to beta particles and allowed it to undergo radioactive decay.
  • The result shows the 2 forks from central region –consistent with bidirectional replication.


FUNCTIONS OF PLASMID
1.VECTORS

  • Plasmids can be used to carry the gene of interest to the host cell.
  • They are commonly used to clone and amplify particular gene.
  • Eg RP4-Plasmid of pseudomonas
  •          Col E1 of E.coli
  •          YEP and Y2P of yeast
  • They contains site for DNA fragmets to insert

2.Protein production

  • Plasmids are used as expression vectors.
  • Scientists essentially turn bacteria (or other cells like yeast) into microscopic factories that churn out a specific protein.

3.Gene therapy

  • In gene therapy, plasmids act as delivery vehicles (non-viral vectors) to transport a "healthy" or therapeutic gene directly into a patient's cells to treat a genetic disorder.
References
1. Lewin's Genes






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