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High and low copy number of plasmids

Plasmid counts in cell.

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High and low copy number of plasmids

  1. 1. HIGH AND LOW COPY NUMBER PLASMIDS. PRESENTEDBY SHABNOORSHAIKH M.SCPART 1 1203
  2. 2. JOSHUA LEDERBERG The termplasmidwas first introducedby the American molecular biologist Joshua Lederberg in 1952. He was knownfor his workin genetics, artificial intelligence and space exploration. He was just 33 years old whenhe won the1958 Nobel prize that bacteria can mate and exchange genes. He sharedthe prize withEdward L. Tatumand George Beadle who won for their work with genetics.
  3. 3. WHAT IS A PLASMID? Like other organisms, bacteriauses its double stranded DNA as their genetic material. Thesegenetic material exist naturally in the cytoplasmof thebacterial cells. In addition to the nucleoidchromosome, bacterial cell often containplasmid as extra chromosomal hereditarydeterminant.
  4. 4.  A plasmid is a DNA molecule that is separatefrom, and can replicate independently of, the chromosomal DNA. They are double strandedand, in many cases, circular. Plasmids usually occur naturallyin bacteria, but are sometimes foundin eukaryotic organisms (e.g., the 2- micrometre-ring in Saccharomycescerevisiae). They are small (a few thousand base pairs) usually carry few genes. PlasmidDNA in bacteriummay be 0.1 – 5%of total DNA.
  5. 5. GENERAL COMPONENTS OF PLASMID Origin of replication:-50-100 bp seq where replicationis initiated. Selectable marker:- antibioticresistant gene. Multiple cloning site:- seq that can be cleavedby restriction enzymes for cloning purposes. Repressor gene:- for regulationof copies.
  6. 6. PLASMIDCOPY NUMBER Copy number is a parameter of bacterialpopulation. Generallydefinedas theratio of number of moles of plasmidDNA to the number of mole of chromosomal DNA in the cell. It varies in rapidly growing bacterial culture. Copy number is controlledby genes on the plasmidand by interactions between the host and the plasmid. It is primarily determinedby the replicon.
  7. 7. CLASSIFICATION OF PLASMIDS. Plasmids may be classified on the basis of the number of copies foundin the host cell. Low copynumber- stringent copy number. Moderate copy number. High copy number- relaxedcopynumber.
  8. 8. STRINGENT PLASMIDS Theseplasmids exists in small numbers that is 1-4copies per cell. Its replicationis closely tiedto host cell chromosomal DNA replication. Here plasmidDNA replicates only onceor twice before cell division Usually large plasmids havelow copy number.
  9. 9. RELAXEDPLASMIDS. Theseplasmids existsin large numbers that is more than100 copies per cell. Its replicationis not dependent on host cell’s chromosomal DNA replication. Here plasmidDNA replicates repeatedlyuntil the proper number is reached. Usually small plasmids havehigh copynumber. They are used for expressionof clonedgene toget higher yields.
  10. 10. EXAMPLES OF PLASMIDS WITHTHEIR COPY NUMBER. PLASMID APPROXCOPY NUMBER F 1 P1 prophage 1 RK2 4-7 pBR322 16 pUC18 30-50 plj101 40-300
  11. 11. ADVANTAGES AND DISADVANTAGES.  ADVANTAGES:- Readilyisolated fromcells. Can be reintroduced intoa bacterial cell. Single restriction site for 1 or more res enzymes. Multiple copynumber so that amplification of the plasmid DNAbecomes easy.  DISADVANTAGES:- Small size hence cannot acceptlarge fragments. Largerthe size lower its replication rate.
  12. 12. REFERENCES GENE BIOTECHNOLOGY by S.N. JOGDAND. PLANTBIOTECHNOLOGYby B.D. SINGH.  http://www.molecular-plant-biotechnology.info/bacterial-vectors/classification-of- plasmids

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