DNA is washed with 70% ethanol to remove some (or ideally all) of the salt from the pellet. If water was used as the wash then DNA would dissolve again and if 100% ethanol was used the salt would not wash off because sodium salts are poorly soluble in ethanol.
because precipitation in 100% ethanol cause removal of all water molecule from DNA and Complete Dehydration,which make them not soluble, So we give 70% wash to let it retain some water molecule when make it soluble.
DNA is washed with 70% ethanol to remove some (or ideally all) of the salt from the pellet. If water was used as the wash then DNA would dissolve again and if 100% ethanol was used the salt would not wash off because sodium salts are poorly soluble in ethanol.
because precipitation in 100% ethanol cause removal of all water molecule from DNA and Complete Dehydration,which make them not soluble, So we give 70% wash to let it retain some water molecule when make it soluble.
Thank you sir.
Dear Dr. Maji, Could you please explain me how Blue White colony selection and theory behind this selection of transformed DNA. thank you again.
A brief information hope helped.
Blue / White colony screening is a strategy to quickly and easily distinguish between recombinant and non-recombinant colonies. It requires a special vector and a special strain of E. coli. It is particularly helpful in tricky cloning strategies such as blunt ended cloning or DNA library preparation.
The first gene in the E. coli lac operon is lacZ, which encodes β-galactosidase (β-gal).During cloning your desire gene incorporates in such a way that disrupt the lacZ gene and thereforelost of β-galactosidase activity.Now we provided 5-bromo-4-chloro-indolyl-β-D-galactopyranoside (x-gal, color less analogue galactose/lactose) into the medium after transformation, When β-galactosidase hydrolyses x-gal, it creates a blue product (5,5'-dibromo-4,4'-dichloro-indigo) only in improper cloned where lacZ gene is intact ). While white colonies indicated disruption of lacZ gene and incorporation of desire insert or proper recombination.
Therefor white colonies are positive selection for cloning experiments while blues are negative.
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