For the quantification by densitometry of supercoiled and relaxed forms of plasmid DNA stained with ethidium bromide and separated in agarose gel there is a correction factor of 1.4 because the relaxed form gives a fluorescence intensity 1.4-fold higher than the supercoiled form. Should the same factor be used to perform the quantification of plasmid DNA stained with GelRed?
probably not unless gelred is an intercalant with the same affinity for DNA than EtBr. You may be able to do an abaque using DNA of known concentration (for both SC and rel and/or OC)
The correction factor for DNA stained ethidium bromide depends on the plasmid size. Correction factor of 1.4 is appropriate for plasmids of about 10 kb. For smaller plasmids we determine it empirically by treating DNA with a nicking endonuclease (many are available from NEB or Themo) and comparing the intensities of the supercoiled and nicked forms. The same can be done for GelRed stained DNA.
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