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COMPUTER EXERCISE Design of PCR and PCR-RFLP experiments This presentation shows all steps of a PCR-RFLP experiment and is a companion of the computer exercise at http://insilico.ehu.es/edu
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To perform a PCR-RFLP experiment, we need a DNA sample.
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Grow the problem cells
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Pick up some bacteria
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Re-suspend the cells in the suitable buffer
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Apply the desired DNA extraction procedure
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The purified DNA is the problem sample
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In this presentation, we will consider two samples obtained from two different bacterial strains
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The reagents for the PCR reaction must be mixed in a new tube H2OH2O Buffer MgCl 2 dNTP Primers Taq pol. Sample
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Add the sterile double-deionized water dd H 2 O H2OH2O Buffer MgCl 2 dNTP Primers Taq pol. Sample
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Buffer Add the 10X PCR buffer H2OH2O Buffer MgCl 2 dNTP Primers Taq pol. Sample
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Add the MgCl 2+ Magnesium ion serves as cofactor for Taq polymerase. MgCl 2 Mg H2OH2O Buffer MgCl 2 dNTP Primers Taq pol. Sample
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dNTP Add the dNTPs mix (dATP, dTTP, dGTP and dCTP) H2OH2O Buffer MgCl 2 dNTP Primers Taq pol. Sample
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Primers Add the primers (forward and reverse primers) H2OH2O Buffer MgCl 2 dNTP Primers Taq pol. Sample
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Taq pol. Add the Taq DNA polimerase H2OH2O Buffer MgCl 2 dNTP Primers Taq pol. Sample
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Add the sample (template DNA) H2OH2O Buffer MgCl 2 dNTP Primers Taq pol. Sample
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The tube will contain all reagents required for PCR reaction 5´ 3´ 5´ MgCl 2 Taq pol. Sample Mg dNTP Primers G A C T
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During PCR reaction the following steps will be repeated 20 to 40 times: denaturation, annealing and extension Denaturation: ~ 1 min 90°C Annealing: ~ 1 min 45-60°C Extension: ~ 1 min 72°C 5´3´ 3´5´
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First cycle, denaturation step: The DNA strands are separated Denaturation: ~ 1 min 90°C Annealing: ~ 1 min 45-60°C Extension: ~ 1 min 72°C 5´3´ 3´5´
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5´3´ First cycle, annealing step: Forward and reverse primers will bind to their target sequences. Denaturation: ~ 1 min 90°C Annealing: ~ 1 min 45-60°C Extension: ~ 1 min 72°C Primer 1 recognition site Primer 2 recognition site 3´5´
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5´3´ 3´5´ First cycle, extension step: Polymerization of DNA by Taq polymerase Denaturation: ~ 1 min 90°C Annealing: ~ 1 min 45-60°C Extension: ~ 1 min 72°C
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T G C C T A G T A G T C G C Denaturation: ~ 1 min 90°C Annealing: ~ 1 min 45-60°C Extension: ~ 1 min 72°C C G G A C T G A T C A T A C G T A G C A T A Mg During extension, nucleotides complementary to target sequence are incorporated in the new DNA strand
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5´3´ 3´5´ Denaturation: ~ 1 min 90°C Annealing: ~ 1 min 45-60°C Extension: ~ 1 min 72°C 5´ 3´ First cycle, extension step: Polymerization of DNA by Taq polymerase
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5´3´ 3´5´ 5´3´ 3´5´ Denaturation: ~ 1 min 90°C Annealing: ~ 1 min 45-60°C Extension: ~ 1 min 72°C Second cycle, denaturation step
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3´5´ 5´3´ 3´5´ Denaturation: ~ 1 min 90°C Annealing: ~ 1 min 45-60°C Extension: ~ 1 min 72°C Second cycle, annealing step
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5´3´ 3´5´ Denaturation: ~ 1 min 90°C Annealing: ~ 1 min 45-60°C Extension: ~ 1 min 72°C 3´5´ 5´3´ Second cycle, annealing step
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5´3´ 3´5´ Denaturation: ~ 1 min 90°C Annealing: ~ 1 min 45-60°C Extension: ~ 1 min 72°C 3´ 5´ 3´5´ 5´3´ 3´ Second cycle, extension step
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In each cycle, the number of target DNA copies will double 1st cicle 2nd cicle 3rd cicle 4rd cicle n cycles 2 1 copies 2 2 copies 2 3 copies 2 4 copies 2 n copies Original DNA
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Prior to RFLP, it is convenient to purify the DNA sample to avoid inhibition of the restriction endonuclease activity
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Many copies of the purified amplicons will be obtained. They will be the sample for therestriction step
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For digestion of the sample DNA (amplicons) the reagents must be mixed in a new tube H2OH2O Buffer Enzyme Sample
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Add the sterile doble-deionized water ddH 2 O H2OH2O Buffer Enzyme Sample
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Buffer Add the 10X buffer H2OH2O Buffer Enzyme Sample
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Add the restriction endonuclease Enzyme H2OH2O Buffer Enzyme Sample
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Add the sample DNA (the purified amplicons) H2OH2O Buffer Enzyme Sample
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C C G T A C G C G T A T A G C G A T A T C G T A T A C G T A C G T A C G T A C C G T A C G C G T A T A G C T A T C G T A T A C G T A C G T A C G T A G A During incubation, the restriction endonuclease will specifically recognize the target sequence.
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C C G T A C G C G T A T A G C G A T A T C G T A T A C G T A C G T A C G T A And it will be cleaved.
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For visualization of the PCR-RFLP experiment DNA samples will be electrophoretically separated in an agarose gel.
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Ladder Molecular weight standards will be added to one line.
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Sample A In the second line, sample A will be added. In this example, amplicons in this sample were not cleaved by the endonuclease.
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Sample B In the third line, sample B will be added. In this example, amplicons were cleaved by the endonuclease.
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During electrophoresis, the ladder and de samples will migrate within the agarose gel.
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LAB LAB For visualization, the gel will be stained.
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1000 500 400 300 200 100 50 Ladder (pb) LAB LAB The molecular weight standards will be used to compute the weight of the bands in samples A and B.
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LAB LAB Sample A contains a unique band of approximately 300 bp. This band was not cleaved by the endonuclease.
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LAB LAB Sample B contains two bands. Cleavage of a 300 bp band containing the target for the endonuclease yielded these 100 and 200 bp bands
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LAB LAB The PCR-RFLP experiment was able to discern the two samples due to the presence of a target sequence for the endonuclease in sample B.
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You may try to solve the online PCR-RFLP exercise available at http://insilico.ehu.es/edu
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