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A260/280 & A260/230 Parametrs for determining purity of a nucleic acid sampl - (Dec/15/2006 )

here is a basic question : why do we need to calculate A260/280 & A260/230 for any isolated RNA or DNA.What is the value of these parameters for a good RNA & DNA prep.
while thawing RNA or DNA(which was kept in -80/-20 degree) say if I have to prepare for a reaction what precautions should I take so that i get a good quality/quantity of nucleic acid for an enzymatic reaction. Is there any difference b/w RNA & DNA handeling.
silly questions, I know they r!!

-Poonam Singh-

These values give information about purity of ypur preparation or isolation.
260 is absorbance max of nucelotides, 280 gives information about protein 'contamination' and 320
(is it 230 or 320?) gives information about chemicals like alcohols, phenols etc... in your sample.

Normally 1,8-2 is good for 260/280
For the other it is above 2.
But these are kind of flexible parameters in the sense that you still can go on with your work even your 260/280 ratio is e.g. 1,6. So it's not a 'strict' and 100% value. It also depends on what you plan to do with your samples anyway.



please have a look at :


Thanx! guys

-Poonam Singh-

u can find a good table of this OD ratio in MOLECULAR CLONING By Sambook

-T. reesei-