Answer to Question #72280 in Genetics for dot

Question

The double-stranded DNA sequence for the coding region of a short peptide is:
5'-ATG-TTT-TCG-ACG-TGC-GAT-TGA-3'
3'-TAC-AAA-AGC-TGC-ACG-CTA-ACT-5'

1, Which strand of DNA, top or bottom is transcribed by RNA polymerase.Explain.

2, A mutation at the second triplet on the coding strand deletes on of the A-T pairs and creates a frameshift mutation. what is the sequence of the peptide now?

Answer 1

1. The bottom strand will be transcribed, because its 3'-end has a TAC triplet. It corresponds to AUG start codon in mRNA. The top strand cannot result in mRNA with the start codon.

2. The resulting DNA sequence is
3' TAC-AAA-GCT-GCA-CGC-TAA-CT 5'
It will result in mRNA with a sequence:
5' AUG-UUU-CGA-CGU-GCG-AUU-GA 3'

The produced protein will have a sequence:

Met-Phe-Arg-Arg-Ala-Ile