Chemical analysis showed that 28% of the total number of nucleotides of this mRNA is accounted for by adenine, 6% – by guanine, 40% – by uracil. What should be the nucleotide composition of the corresponding section of double-stranded DNA, the information from which is “rewritten” for this mRNA?
1. Knowing that the chain of the RNA molecule and the working chain of the DNA molecule are complementary to each other, we determine the content of nucleotides (in%) in the working DNA chain:
in the mRNA chain G = 6%, so in the working DNA chain C = 6%;
in the mRNA chain A = 28%, which means in the working DNA chain T = 28%;
in the mRNA chain Y = 40%, which means in the working DNA chain A = 40%;
2. Determine the content in the mRNA chain (in%) of cytosine.
we summarize the content of three other types of nucleotides in the mRNA chain: 6% + 28% + 40% = 74% (G + A + Y);
determine the proportion of cytosine in the mRNA chain: 100% – 74% = 26% (C);
if in the mRNA chain C = 26%, then in the working DNA chain G = 26%.
Answer: C = 6%; T = 28%; A = 40%; G = 26%
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