Which strand of the DNA is the coding strand, serving as a 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.
A. Strand 1 B. Strand 2 C. Both strands 1 and 2 D. Neither strand 1 nor 2 E. Too little information to tell
The correct answer to this question is option B – Strand 2 The DNA strand that served as the template strand (coding strand) in the synthesis of mRNA shown above is DNA strand #2. Complementary base pairing is the basis of RNA transcription. If you take a look at G in DNA strand #2 and C in mRNA, you can tell that they are complementary. Same as T in DNA strand #2 and U in mRNA.
A simple way to identify this is to know that mRNA always looks likes the non-coding strand. This is because both the non-coding strand and are transcribed from the same sequence of coding strand. If you look at the chart carefully, you will see that DNA strand #1 is identical to mRNA aside that thymidine is present in DNA and it is replaced with Uracil in RNA.
The correct answer is option B From the image above, we can tell that the coding strand of DNA that serves as the template strand for mRNA synthesis is DNA strand #2. Looking at the ratio of complementary nucleotides that bind to each other are similar to that of DNA strand 2. Take for instance, the bond between A and T (the A in mRNA is complementary to that of T in DNA strand 2). Same as the U in mRNA is complementary to A in strand 2 of DNA. Also, G to C on both strands are complementary.