Question

The transcribed portion of a DNA sequence for a gene is shown below. Identify the mRNA sequence and the polypeptide sequence that would be produced from this gene. Also, identify the specific type of DNA mutation and protein mutation that would result if the underlined A/T basepair was mutated to a C/G basepair. NOTE: Assume RNA polymerase is moving left to right across the page. 

3' - TATACGCGATATGGATTC - 5 

5'- ATATGCGCTATACCTAAG - 3 

Answer 1

DNA sequence:

3'-TATACGCGATATGGATTC-5'

5'-ATATGCGCTATACCTAAG-3'

RNA polymerase is moving left to right across the page.

we know RNS polymerase can synthesize RNA in 5' to 3' direction. So the template strand is:

3'-TATACGCGATATGGATTC -5'

mRNA : 5'-AUAUGCGCUAUACCUAAG-3'

polypeptide: Met-Arg-Tyr-Thr

AUG is the start codon and UAA is the stop codon.

If the underlined A/T base pair was mutated to C/G basepair the DNa sequence will be:

3'-TATACGCGATCTGGATTC-5'

The resulting mRNA will be -

5'-AUAUGCGCUAGACCUAAC-3'

polypeptide: Met-Arg

Due to mutation the 3rd codon of the mRNA became a stop codon UAG. so the translation will be terminated at that point. This a nonsense mutation.