|MadSci Network: Molecular Biology|
hi. its true that the buffers are acidic for RNA work and slightly basic (usually around pH 8)for DNA extractions. If you place DNA in a strong bacic solution the bonds between the strands will be cleaved and the 2 stands will not be able to re join. RNA can survive and contaminate when preforming a DNA extraction, unless specific steps are used to remove the RNA ie using RNase. The acidic conditions for RNA extractions is due to a number of problems when dealing with RNA. DNA is a major contaminant which needs to be removed as it can interfer with RT-PCR etc. Also RNase has very little activity in acidic condition and is de-activated by guanidinium thiocyanate. Often the RNA extraction buffers are 5M G.thio and pH 4.8ish. hope that helps regards Sean Admin note: Another reason for the disparity in nucleic acid extraction buffers is tied to the phenol extractions commonly used to purify the nucleic acids away from cellular proteins: DNA is soluble in even mildly acidic phenol while RNA is not; so a good way to purify RNA's away from genomic DNA is to perform an acidic phenol extraction. Since phenol is itself a buffer, these extraction work best if the sample buffer is also acidic. Conversely, if DNA is being isolated, any acidity present during phenol extraction could greatly reduce yield.
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