Question

Shown below is the DNA sequence of a gene from a virus that encodes a short viral peptide. Also shown is the sequence of the mRNA synthesized from this gene. genomic DNA sequence:

5'-TGGACTAGCTCATGTGCGAGTCCTGACGCTGACTAGGTTTATGCA-3'

3'-ACCTGATCGAGTACACGCTCAGGACTGCGACTGATCCAAATACGT-5'

mature mRNA sequence (G* = 5’ cap):

5'-G*UCAUGUGCGAACGCUGACUAGGAAAAAAAA...-3'

A) In the genomic DNA sequence shown above, draw a box around each of the two exons in the gene.

B) Where does the promoter reside (to the left or to the right)?

C) In the mRNA above, some nucleotides are present that are not encoded in the genomic DNA sequence. What two processes have occurred to add these nucleotides to the mRNA? D) Is this virus more likely to replicate in prokaryotic or eukaryotic cells? Briefly explain your reasoning.

Answer 1

A. See the image

B. See the image

C. Post-transcriptional modifications
i. Splicing = Removal of introns and joining of exons
ii. Capping = Addition of 5-methylguanosine cap at the 5'-end
iii. Tailing = Addition of adenine residues at the 3'-end

D. The host cell of the virus must be a eukaryote. This is due to the fact that post-transcriptional modifications occur only in eukaryotes.