A DNA double helix is composed of two strands of complementary (not identical) D

Question

A DNA double helix is composed of two strands of complementary (not identical) DNA. One strand, labeled as the template strand, serves and the template from which a complementary single strand mRNA is transcribed. The other strand, labeled as the coding strand, can be used to "read" the protein sequence coded by the DNA. Below is the sequence for a template strand of the tryptophan operon gene. Write-out the sequence for the coding strand (in the standard 5' rightarrow 3' notation) Calculate the composition (mole fraction) of [A], [T], [G], and [C] for the template strand and for the coding strand of DNA. Are they the same or different for each strand? Calculate the composition (mole fraction) of [A + T] and [G + C] for the template strand and for the coding strand of DNA. Are they the same or different for each strand?

Explanation / Answer

A)

5' - TAC GGC GGT CGC CTT GAC CGC CGA CAC CCT AAT TGA CGC GCA GCG GCG - 3'

B)

Calculate total number of bases and then divide each base by total number of bases to get percentage composition

For template strand mole fraction :A = 7 / 48 = 0.15 ; T = 8 / 48 = 0.17 ; G = 18 / 48 = 0.38 ; C = 15 / 48 = 0.31

For coding strand mole fraction : A = 8 / 48 = 0.17 ; T = 7 / 48 = 0.15 ; G = 15 / 48 = 0.31 ; C = 18 / 48 = 0.37

Hence, mole fraction of each base is different for template and coding strand

C)

For template strand [A + T] = [14.6 + 16.6] = 0.31

For template strand [G + C] = [37.5 + 31.2] = 0.69

For coding strand [A + T] = [16.6 + 14.6] = 0.31

For coding strand [G + C] = [31.2 + 37.5] = 0.69

Hence, mole fraction of [A +T] and [G + C] is same for template and coding strand

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