Nucleic Acids and the Genetic Material Problem Set 1

Problem 15: DNA template for mRNA synthesis

You have obtained a sample of DNA, and you transcribe mRNA from this DNA and purify it. You then separate the two strands of the DNA and analyze the base composition of each strand and of the mRNA. You obtain the data shown in the table to the right. Which strand of the DNA is the coding strand, serving as a template for mRNA synthesis?
DNA strand #1 19.1 26.0 31.0 23.9 0
DNA strand #2 24.2 30.8 25.7 19.3 0
mRNA 19.0 25.9 30.8 0 24.3

A. Strand 1
B. Strand 2
The mRNA uses one of the DNA strands as a template, and thus will be complementary. The non-coding strand of DNA is also complementary to the template, and thus the mRNA and noncoding strands should have the same base compositions, with U replacing T. DNA strand I has the same base composition as the mRNA, with the replacement of T by U.
C. Both strands 1 and 2
D. Neither strand 1 or 2
E. Too little information to tell

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Sunday, September 29, 1996
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