Purification of PCR products is generally not necessary. It is advantageous to gel purify the target DNA fragment if the PCR product is contaminated by either non-specific amplification products, primer-dimers or large quantities of unused PCR primers.
Purification of DNA from a PCR reaction is typically necessary for downstream use, and facilitates the removal of enzymes, nucleotides, primers and buffer components.
Generally the first buffer PX contains chaotrophic salts and alcohol which destabilises both protein or dna and minimises the way dna interacts with water so making it bind much better to the silica particles in the dna binding filter. The first wash solution WS contains much less of the chaotrophic salts and washes protein and polysaccharide residues off the column leaving the dna bound to the filter.
The second wash solution WN is mainly ethanol to wash away salts so that the dna can be washed off .
The elution solution is usually either water or dilute 10mM tris at alkaline pH and the dna dissolves in this and elutes off the silica matrix
PCR purify: Purification of PCR products is generally not necessary. If you are not sure or additional minor products are produce from your PCR reaction then required to purify.
PX buffer: It is used in DNA cleanup procedures and enables efficient binding of single or double stranded PCR products to the spin-column membrane. In this case, we can also used buffer PB.
WN & WS buffer: Both are wash buffer. WN buffer is used to remove protein residues and degraded RNA residues on the membrane. WS buffer is used to remove salt residues on the membrane. In this case, we can use buffer PE for removal of excess salt from the membrane.
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