Question

1. Below is the double-stranded DNA sequence of part of a hypothetical yeast genome, which happens to contain a very small gene. Transcription starts at the Transcription Start Site (TSS) after the promoter (shown in yellow), and proceeds in the direction of the arrow. Transcription stops at the end of the Transcription Terminator (shown in blue).

5' GTATAAATCCCTATGTTGACTTCAAAGGGCCCATGGAAGGGCTGATTCCTAAGA 3'

3' CATATTTAGGGATACAACTGAAGTTTCCCGGGTACCTTCCCGACTAAGGATTCT 5'

a) Which strand of DNA shown, the top or the bottom, is the template strand?

b) What is the sequence of the mRNA produced from this gene? Write the sequence and label the 5’ and 3’ ends.

c) What is the sequence of the polypeptide produced from the mRNA in (b)? Write the sequence and label the N and C termini.

d) If a point mutation changed the bold G/C (top/bottom) base pair was changed to an C/G (top/bottom) base pair instead, what would be the new sequence of the mRNA? What would be the sequence of the protein?

Answer 1

Given DNA sequence:

5' GTATAAATCCCTATGTTGACTTCAAAGGGCCCATGGAAGGGCTGATTCCTAAGA 3'

3' CATATTTAGGGATACAACTGAAGTTTCCCGGGTACCTTCCCGACTAAGGATTCT 5'

a) The top strand is the template strand.

b) The sequence of the mRNA produced from this gene is:

5' GUAUAAAUCCCUAUGUUGACUUCAAAGGGCCCAUGGAAGGGCUGAUUCCUAAGA 3'

c) The sequence of the polypeptide produced from the mRNA:

N-Val-STOP-Ile-Pro-Met-Leu-Thr-Ser-Lys-Gly-Pro-Trp-Lys-Gly-STOP-Phe-Leu-Arg-C

d) If a point mutation changed the bold G/C (top/bottom) base pair was changed to C/G (top/bottom) base pair instead, the new sequence of the DNA will be:

5' GTATAAATCCCTATGTTGACTTCAAAGGGCCCATGCAAGGGCTGATTCCTAAGA 3'

3' CATATTTAGGGATACAACTGAAGTTTCCCGGGTACGTTCCCGACTAAGGATTCT 5'

The sequence of the mRNA will be:

5' GUAUAAAUCCCUAUGUUGACUUCAAAGGGCCCAUGCAAGGGCUGAUUCCUAAGA 3'

The sequence of the polypeptide or protein produced from the mRNA:

N-Val-STOP-Ile-Pro-Met-Leu-Thr-Ser-Lys-Gly-Pro-Cys-Lys-Gly-STOP-Phe-Leu-Arg-C