An analyst suspects that an unknown sample containing double-stranded DNA also c
ID: 145974 • Letter: A
Question
An analyst suspects that an unknown sample containing double-stranded DNA
also contains a significant quantity of carbohydrate. The DABA assay for total
DNA yields a concentration of 44 ? 3 mg/mL, while the ferricyanide assay for
reducing carbohydrate, conducted on an 10-fold dilution of the unknown sample,
yielded a result of 1.8 ? 0.3 mg/mL. The formula weight of one deoxynucleotide
monophosphate residue of DNA is ?330 g/mol, while monosaccharides have a
molecular weight of ?180 g/mol. Assuming that interference in the DABA
assay is due solely to reducing monosaccharides, and that one monosaccharide
molecule yields the same absorbance as one deoxynucleotide monophosphate in
the DABA assay, calculate the actual quantity of DNA in the sample. Suggest a
more selective assay for double-stranded DNA that could be used to confirm this
value.
Explanation / Answer
Although the present biochemical analytical method is suitable for investigation quantitative as well as qualitative estimation of DNA and other biomolecules, it is not replicative in nature and involves chances of manual errors.
Spectrophotometric methods are highly advanced and accurate measures to investigate not only the concentrations of nucleic acids, but also their integrity and strandedness. These methods are also suitable to quantize the presence of any contaminant such as carbohydrate or proteins. Thus, an advanced spectrophotometric analysis can be performed on a very less sample volume, say 1 or 2 micro litre to validate these biochemical results.