Question

The following is a portion of an mRNA sequence:
3'-AUCGUCAUGCAGA-5'
Part A
During transcription, was the adenine at the left-hand side of the sequence the first or the last nucleotide added to the portion of mRNA shown?
a. the first
b. the last
Part B
Write out the sequence of the DNA duplex that encodes this mRNA segment.

Answer 1

Answer:

Part A: Adenine at the 3'-end would be the last nucleotide added to the portion of mRNA.

Part B: Sequence of DNA duplex would be

5'-TAGCAGTACGTCT-3'

3'-ATCGTCATGCAGA-5'

Transcription is the process by which nucleotide sequence of template strand of the DNA is copied into the nucleotide sequence of RNA with the help of RNA polymerase enzyme.

This enzyme read the template strand of DNA in 3' to 5' direction and create a complementary RNA in 5' to 3' direction. It is because RNA polymerase can add nucleotide only to the 3' end of the RNA.

The nucleotide sequence of RNA produced is complementary to the DNA template strand and is exactly same as that of non-template or coding strand. The only difference is the presence of uracil (in RNA) in place of thymine (in DNA).

Hence, the nucleotide sequence of DNA template strand of given mRNA would be 5'-TAGCAGTACGTCT-3' and that of the non-template strand would be 3'-ATCGTCATGCAGA-5'.