in many protocol for DNA extraction I have seen that 100% ethanol (absolute ethanol) is used first for DNA precipitation (washing) then 70% ethanol.
why does it like that and what is the reason for ordering like that?
Very simple as DNA is insoluble in alcohols (Ethanol & Isopropanol) we use 100% alcohols for precipitation so we get good amount of DNA. Washing with 70% alcohol is to remove the excess of salts (that might have come along with the extraction buffers) i.e. the excess of salts dissolve in the 30% of water.
If you use 70% or 80% of alcohol for precipitation the DNA isolated dissolve in the water, what is the use of isolating DNA and what analysis you do!!! Hope your doubt is cleared.
Very simple as DNA is insoluble in alcohols (Ethanol & Isopropanol) we use 100% alcohols for precipitation so we get good amount of DNA. Washing with 70% alcohol is to remove the excess of salts (that might have come along with the extraction buffers) i.e. the excess of salts dissolve in the 30% of water.
If you use 70% or 80% of alcohol for precipitation the DNA isolated dissolve in the water, what is the use of isolating DNA and what analysis you do!!! Hope your doubt is cleared.
in the first instance you are adding 100% alcohol to a volume of aqueous salts and dna so the final concentration will be close to 70% after mixing so there is little difference between the precipitation and the wash stages
The first step as Jety and Paul said is to precipitate the DNA. Adding 70% ethanol will dissolve the DNA in 30% water. Is critical to dry the extracted DNA to avoid interference of ethanol during PCR mixture
Jetty Ramadevi Ma'am your answer is just so precise and excellent!
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