Studies have shown that in the mRNA molecule, 34% of the total number of nitrogenous bases are in guanine, 18% in uracil, 28% in cytosine, and 20% in adenine. Determine the percentage of the nitrogenous bases of the double-stranded DNA, one of the chains of which served as a matrix for the synthesis of this mRNA.
– According to the principle of complementarity, we determine the percentage composition of nitrogen bases of the corresponding transcribed DNA chain. It contains 34% cytosine (complementary to guanine mRNA), 18% adenine (complementary to uracil mRNA), 28% guanine (complementary to cytosine mRNA) and 20% thymine (complementary to adenine mRNA).
– Based on the composition of the transcribed chain, we determine the percentage composition of the nitrogenous bases of the complementary (non-transcribed) DNA chain: 34% guanine, 18% thymine, 28% cytosine and 20% adenine.
– The percentage of each type of nitrogenous bases in double-stranded DNA is calculated as the arithmetic average of the percentage of these bases in both chains:
C = G = (34% + 28%): 2 = 31%
A = T = (18% + 20%): 2 = 19%
Answer: the corresponding double-stranded DNA contains 31% cytosine and guanine, 19% adenine and thymine.
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