Question

Whta is the approximate molecular weight of duplex dna required to code for glyceraldehyde phosphate dehydrogenase (mw 40,000)

Answer 1

If the molecular weight of the protein is 40,000 
Then number of amino acids will be 40,000/110= 363.63
(110 is average molecular weight of one amino acid)
One amino acid is coded by three nucleotide thus 363.63 (≅325, average molecular weight of one nucleotide) amino acids coded by approx 1000 nucleotide.
Average molecular weight of one nucleotide is 325
Average molecular weight of RNA will be 325 x 1000 = 325000
Average molecular weight of duplex DNA will be 325000 X 2 = 650000 (≅700000)