Molecular weight determination nucleic acids

Determination of the size or molecular weight of nucleic acids is crucial in molecular biology. This importance is increased by the introduction of the PCR, which allows an individual to be identified (e.g. a pathogen bacteria) or the genetic links between individuals and allows the prediction or diagnosis of diseases. 

UV absorption spectroscopy is further used to determine nucleic acid concentration. The average molecular weight of a nucleotide is 320 and 50[rgml concentration of a random sequence DNA provides the A260 absorbance of 1 in a 1 cm pathlength cell. In practice, the absorption coefficient of DNA is precisely determined by enzymatic hydrolysis of DNA to monomers and calculation using the absorption coefficients of the monomers, or by measurement of thermally denatured DNA. The absorption of the denatured DNA sample is calculated on the basis of absorption coefficients of the constituent mono- and dinucleotides. 

Results on DNA-based biosensors will be presented they have been used mainly for two kind of applications 1) for the determination of low-molecular weight compounds witlr affinity for nucleic acids and 2) for the detection of hybridization reaction. 

As previously discussed in this chapter, the molecular size of protein or nucleic acid samples may be determined by electrophoresis. This requires the preparation of standard curves of log molecular weight versus fi (mobility) using standard proteins or nucleic acids. 

Mass Spectrometry Usage of analytical devices that can determine the mass (or molecular weight) of proteins and nucleic acids, the sequence of protein molecules, the chemical organization of almost all substances and the identification of gram-negative and gram-positive microorganisms. 

The method of determining the molecular weight of an unknown nucleic acid sample is exactly the same as that described for the determination of protein molecular weight in SDS-PAGE. 

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