DNA extraction - To measure A260/280 (Jun/16/2007 )

hello,
i have a problem with my genomic DNA
We extract the genomic DNA for banana,
but the ratio for A260/280 is more than 2.0.
Can't somebody tell me what the problem with my DNA
and how to solve

A much more than 2.0? What kind of extraction did you perform? How much DNA do you have?

High concentrations of DNA or possible proteins can shift the shape and location of your spectrum measurement, leading to awkward A260/A280 ratios. A measurement figure would be useful to pinpoint a possible cause.

i'll say too much DNA.. many time my 260/280 ratio of maxi DNA comes 2.3..

run on the gel n see how ur DNA look like..

Ratio looks very fine to me. I can imagine a nice peak at 260 nm and a nice dna band in electrophoresis

Next time, try to measure a lower concentration by diluting the sample. I don't know what system you use but, as I said earlier, high concentration of measured DNA shifts the ratio. I wouldn't worry about it too much with a DNA concentration of 2.5 ug/ul in the measured sample.

with nanodrop you can detect concentration up to 3 ug/ml. but with conventional specs linearity would be till 50 ng/ul for an OD of 1.. correct me please if am wrong.. so in such case.. as suggestes.. u have to dilute ur sample

1.) Make two dilutions: like 1:100 and 1:1000
2.) Take three readings of each dilutions
See the result

i am bit confused............
so far i know A260/280 ratio for pure DNA is from 1.8 to 2.2
i cant understand how can u calculate DNA concentration from this ratio???
from my maxiprep i got 1.8 to 2.2 ratio and the DNA concentation i got DNA varies from 0.5 to 3 ug/ul

well pure DNA ratio is from 1.7 to 2.0
RNA gives ratios higher

But those ratios don't mean anything about concentration
In general when high ratios are observed, it may come from a non sufficent dilution. A too much concentrated solution alters measurements if OD is >1 (fro my aparatus it's the case).