average molar mass of dna

Question

The human body is said to contain approximately 50.0 grams of DNA in the entire body. If the number of nucleotides in ONE STRAND of DNA is approximately 3.0 x 106, and the average molar mass of a nucleotide is 327 g/mol, what is the average molar mass of an entire DNA double helix?

Answer 1

You are off by 3 orders of magnitude. The number of base residues (not nucleotides, which are monomers) in a single polymeric strand of DNA is 10⁹.

 

10⁶ is just a million. That is nowhere close, let alone approximately, to the actual amount of DNA in a single strand of human DNA.

 

 

Answer 2

The entire DNA double helix has 2 strands.  Thus,

3.0x10⁶ nucleotides/strand x 2 strands = 6.0x10⁶ nucleotides

6.0x10⁶ nucleotides x 327 g/nucleotide = 1.962x10⁹ g = 2.0x10⁹ g/mole = molar mass of double stranded DNA

NOTE:  The fact that the human body contains 50 grams of DNA does not enter into solving this problem.