Expert: Dana Krempels, Ph.D. - 12/8/2010

Question
This was an extra credit question to be added to the final.  I have taken my final as of Monday and all my classes are now complete.  But I did want to know how to solve this problem as I will be changing my major next semester to something else.  The question is as follows:

a) Calculate the length (in nucleotide pairs or base pairs) of a dbl-stranded DNA molecule with a molecular weight of 3 x 10(7thpwr)g/mole. (the avg molecular wt of a nucleotide pair is 620 g/mole)

b) For same DNA in above, calculate the length of the molecule in nanometers(nm), kn owing the following two critical facts: 1)the average nucleotide pair (bp) of DNA measures 3.4 Amgstroms.  That is every rise of the DNA dbl helix by 1 bp, it occupies 3.4 Angstrom units. & 2) 1 Angstrom unit = 0.1 nm  

Answer
Dear Cheryl,

I'm not going to give you the *whole* answer, since this sounds remarkably like a homework problem. But I can point you in the right direction.

The first one is a simple math problem.  Just divide 30,000,000 by 620, and you'll have the number of moles of nucleotide.  If you know how many nucleotides there are in a mole (Avogadro's number:  6.02 x 10 to the 23power), then you can figure the rest of this out.  If it's double stranded, then divide this number by two, and you'll have the length (in base pairs) of the strand.

From this information, you should be able to do the further math in part (b).  It's a multiplication problem.

Hope that clears things up.

Dana