booraad
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1 cm3 of DNA I will be given has been extracted from 1 g of calf thymus tissue.
How do I calculate the percentage (%w/w) of DNA in calf thymus tissue?

What is:
(i) the wavelength of maximum absorption (lambda max) of DNA and (ii) the concentration of DNA (in microgram/cm3) that corresponds to 1.0 absorbance unit.
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Iscariot
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You need to plot a calibration curve using known standards to do part (ii), against which you can extrapolate how much DNA corresponds to 1.0 absorbance.

For part (i) I have to say it's not exactly straight forward... In our practicals the absorbance needed is always given to us to use. I suppose if you wanted to discover what the maximum absorption is then I'd probably just stick a sample with pure DNA in it and see what wavelength gives you optimal absorbance.

That would seem kind of time consuming with a spectrophotometer unless you had one of those automated ones (which I know exist but I've never used).

When you have plotted your calibration curve you can deduce the weight of DNA present on the basis of it's absorption, which you can divide by 1g of calf thymus tissue, giving you a %w/w.

Hopefully this helps...
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