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  1. 1. WELCOMEN <ul><li>BIOTECHNOLOGY SITE </li></ul>
  2. 2. Gene Cloning
  3. 3. Cloning - a definition <ul><li>From the Greek - klon, a twig </li></ul><ul><li>An aggregate of the asexually produced progeny of an individual;a group of replicas of all or part of a macromolecule (such as DNA or an antibody) </li></ul><ul><li>An individual grown from a single somatic cell of its parent & genetically identical to it </li></ul><ul><li>Clone: a collection of molecules or cells, all identical to an original molecule or cell </li></ul>
  4. 4. DNA CLONING A method for identifying and purifying a particular DNA fragment (clone) of interest from a complex mixture of DNA fragments, and then producing large numbers of the fragment (clone) of interest.
  5. 5. Gene cloning <ul><li>When DNA is extracted from an organism, all its genes are obtained </li></ul><ul><li>In gene (DNA) cloning a particular gene is copied (cloned) </li></ul>
  6. 6. Why Clone DNA? <ul><li>A particular gene can be isolated and its nucleotide sequence determined </li></ul><ul><li>Control sequences of DNA can be identified & analyzed </li></ul><ul><li>Protein/enzyme/RNA function can be investigated </li></ul><ul><li>Mutations can be identified, e.g. gene defects related to specific diseases </li></ul><ul><li>Organisms can be ‘engineered’ for specific purposes, e.g. insulin production, insect resistance, etc. </li></ul>
  7. 7. Sources of DNA for Cloning <ul><li>1) Chromosomal DNA </li></ul><ul><li>2) RNA converted to cDNA </li></ul><ul><li>3) PCR-amplified DNA </li></ul>
  8. 8. PCR-amplified DNA
  9. 9. Cloning Tools <ul><li>Restriction endonucleases </li></ul><ul><li>Ligase </li></ul><ul><li>Vectors </li></ul><ul><li>Host </li></ul><ul><li>Methods for introducing DNA into a host cell </li></ul>
  10. 10. Cutting DNA <ul><li>Restriction endonucleases (restriction enzymes) </li></ul><ul><ul><li>sticky ends </li></ul></ul><ul><ul><li>blunt ends </li></ul></ul><ul><li>Nomenclature </li></ul><ul><ul><li>Eco RI </li></ul></ul><ul><ul><li>E = genus ( Escherichia ) </li></ul></ul><ul><ul><li>co = species ( coli ) </li></ul></ul><ul><ul><li>R = strain </li></ul></ul><ul><ul><li>I = # of enzyme </li></ul></ul>
  11. 11. Blunt & Sticky ends
  12. 12. Pasting DNA <ul><li>Complementary ends (sticky ends) H-bond </li></ul><ul><li>Ligase forms phosphodiester bond to seal strands together. </li></ul>
  13. 13. Cloning vectors allowing the exogenous DNA to be inserted, stored, and manipulated mainly at DNA level. 1 Plasmid vectors 2 Bacteriophage vectors 3 Cosmids 4 BACs & YACs
  14. 14. Plasmid vectors <ul><li>Advantages: </li></ul><ul><ul><li>Small, easy to handle </li></ul></ul><ul><ul><li>Straightforward selection strategies </li></ul></ul><ul><ul><li>Useful for cloning small DNA fragments </li></ul></ul><ul><ul><li>(< 10kbp) </li></ul></ul><ul><li>Disadvantages: </li></ul><ul><ul><li>Less useful for cloning large DNA fragments </li></ul></ul><ul><ul><li>(> 10kbp) </li></ul></ul>Plasmid vectors are double-stranded, circular, self-replicating, extra-chromosomal DNA molecules.
  15. 15. A plasmid vector for cloning <ul><li>Contains an origin of replication, allowing for replication independent of host’s genome. </li></ul><ul><li>Contains Selective marker s: Selection of cells containing a plasmid </li></ul><ul><li>twin antibiotic resistance </li></ul><ul><li>blue-white screening </li></ul><ul><li>Contains a multiple cloning site ( MCS ) </li></ul><ul><li>Easy to be isolated from the host cell. </li></ul>
  16. 16. Plasmid vectors
  17. 17. Bacteriophage vectors <ul><li>Advantages: </li></ul><ul><ul><li>Useful for cloning large DNA fragments </li></ul></ul><ul><ul><li>(10 - 23 kbp) </li></ul></ul><ul><ul><li>Inherent size selection for large inserts </li></ul></ul><ul><li>Disadvantages: </li></ul><ul><ul><li>Less easy to handle </li></ul></ul>
  18. 18.  vectors <ul><li>Left arm : </li></ul><ul><ul><li>head & tail proteins </li></ul></ul><ul><li>Right arm : </li></ul><ul><ul><li>DNA synthesis </li></ul></ul><ul><ul><li>regulation </li></ul></ul><ul><ul><li>host lysis </li></ul></ul><ul><li>Deleted central region : </li></ul><ul><ul><li>integration & excision </li></ul></ul><ul><ul><li>regulation </li></ul></ul>
  19. 20. Cosmid vectors <ul><li>Advantages: </li></ul><ul><ul><li>Useful for cloning very large DNA fragments </li></ul></ul><ul><ul><li>(32 - 47 kbp) </li></ul></ul><ul><ul><li>Inherent size selection for large inserts </li></ul></ul><ul><ul><li>Handle like plasmids </li></ul></ul><ul><li>Disadvantages: </li></ul><ul><ul><li>Not easy to handle very large plasmids (~ 50 kbp) </li></ul></ul><ul><ul><li>combine the properties of plasmid vectors with the useful properties of the l cos site </li></ul></ul>
  20. 22.  ZAP
  21. 23. BACs and YACs <ul><li>Advantages: </li></ul><ul><ul><li>Useful for cloning extremely large DNA fragments </li></ul></ul><ul><ul><li>(100 - 2,000 kbp) </li></ul></ul><ul><ul><li>This is very important for genome sequencing projects </li></ul></ul><ul><li>Disadvantages: </li></ul><ul><ul><li>Not easy to handle extremely large DNA molecules </li></ul></ul>BACs : B acterial A rtificial C hromosome s YACs : Y east A rtificial C hromosome s
  22. 24. BAC vector <ul><li>ori S and ori E mediate replication </li></ul><ul><li>par A and par B maintain single copy number </li></ul><ul><li>Chloramphenicol R marker </li></ul>
  23. 25. YAC vector <ul><li>Capable of carrying inserts of 200 - 2000 kbp in yeast </li></ul>telomere telomere centromere URA3 ARS HIS3 replication origin markers large inserts
  24. 26. What determines the choice vector? <ul><li>insert size </li></ul><ul><li>vector size </li></ul><ul><li>restriction sites </li></ul><ul><li>copy number </li></ul><ul><li>cloning efficiency </li></ul><ul><li>ability to screen for inserts </li></ul><ul><li>what down-stream experiments do you plan? </li></ul>
  25. 27. Expression vector
  26. 28. expression vector pSE420 <ul><li>polylinker: insert desired DNA </li></ul><ul><li>amp resistance </li></ul><ul><li>trc promoter </li></ul><ul><li>lacO (operator) </li></ul><ul><li>Shine-Dalgarno (S/D) site </li></ul><ul><li>(ribosome binding) </li></ul><ul><li>T1, T2 transcription terminators </li></ul><ul><li>lacI ( lac repressor) </li></ul>growth inducer added cloned gene expressed; product produced (Fig. 31.4, p. 1002, Madigan et al.) Btech10
  27. 29. <ul><li>insertion of foreign DNA at Bam HI site </li></ul><ul><li>tet resistance gene inactivated </li></ul><ul><li>transformants carrying foreign DNA are amp resistant but tetracycline sensitive </li></ul>(Fig. 10-42, p. 309, Madigan et al.) transformation: transfer of genetic information via free DNA Btech6 How to clone DNA
  28. 30. How to clone DNA <ul><li>Isolation of cloning vector (bacterial plasmid) & gene-source DNA (gene of interest) </li></ul><ul><li>Insertion of gene-source DNA into the cloning vector using the same restriction enzyme; bind the fragmented DNA with DNA ligase </li></ul><ul><li>Introduction of cloning vector into cells (transformation by bacterial cells) </li></ul><ul><li>Cloning of cells (and foreign genes) </li></ul><ul><li>Identification of cell clones carrying the gene of interest </li></ul>
  29. 31. Screening of the clone <ul><li>The medium in this petri dish contains the antibiotic Kanamycin </li></ul><ul><li>The bacteria on the right contain Kanr, a plasmid that is resistant to Kanamycin, while the one on the left has no resistance </li></ul><ul><li>Note the difference in growth </li></ul>
  30. 32. Blue/White Color Screening lacZ lacZ insert functional enzyme nonfunctional enzyme X-gal product X-gal product
  31. 33. Selecting Colonies with Recombinant Plasmids
  32. 34. Colony hybridization <ul><li>DNA probe available? </li></ul><ul><ul><li>part of same gene </li></ul></ul><ul><ul><li>orthologue from another species </li></ul></ul><ul><ul><li>synthetic oligonucleotide </li></ul></ul>Figure 6.12
  33. 35. bacteriophage lambda as a cloning vector (Fig. 10.44, p. 311, Madigan et al.) transduction: transfer of host genes from one cell to another by a virus Btech7
  34. 36. Other methods for introducing DNA <ul><li>electroporation: the use of an electric pulse to enable cells to take up DNA </li></ul><ul><li>millisecond-length pulses open small pores in cell membranes </li></ul><ul><li>DNA can move into/out of the cells via pores </li></ul>cell plasmid transformant plasmid donor desired transformant microprojectile “gun” Btech8
  35. 37. transgenic plants may be produced with binary vector system in Agrobacterium tumefaciens (Fig. 31.11, p. 1014, Madigan et al.) <ul><li>(a) generalized plant cloning vector </li></ul><ul><ul><li>ends of T-DNA (red) </li></ul></ul><ul><ul><li>ori ( E. coli ), ori ( A. tumefaciens ) </li></ul></ul><ul><ul><li>resistance markers (kan, spec) </li></ul></ul>(b) can clone in E. coli; transfer to A. tumefaciens by conjugation (c) D-Ti = engineered Ti (to remove pathogenesis genes) (d) D-Ti will mobilize T-DNA of vector -> plant cells grown in tissue culture (e) whole plants can be regenerated from recombinant cell Btech15
  36. 38. End ARRIVIDIERCI………

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