Question 3 Shown below is a double-stranded bacterial (E. coli) DNA sequence cod

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Question 3 Shown below is a double-stranded bacterial (E. coli) DNA sequence coding for a hypothetical protein. Both strands are shown; the top strand reads 5 to 3' left to right, while the bottom strand reads 5 to 3 right to left. The nucleotides are numbered 1 to 100. NOTE: For this problem, transcription begins with and includes the red and underlined C/G (top strand/bottom strand) base pair and RNA polymerase proceeds from left to right along the DNA 20 40 5'-GTGTCCGTCTAATATTGTGAGATGTTATATCCCGCCGTCAACACCATCAA-3 3'-CACAGGCAGATTATAACACTCTACAATATAGGGCGGCAGTTGIGGTAGTT-5 100 60 80 5'-ACAGGATAATCGCCTGCTGGGGCAAAGGCGGTGAAGGTAAAGGTGTTGCC-3 3'-TGTCCTATTAGCGGACGACCCCGTTTCCGCCACTTCCATTTCCACAACGG-5 a) Which strand is used as a template for transcription, the top or the bottom? T b)Where would the promoter be relative to the start of transcription? GALA (nd AAT o) What are the first 15 nucleotides of the resulting mRNA? Indicate the 5' and 3' ends of the mRNA.S-CUAAVAWFU d) What are the first 5 amino acids translated from the resulting mRNA? Indicate the amino (NH3') and carboxy (Coo') termini of the protein. NH e) Do the underlined nucleotides TAA (indicated in blue) encode a stop codon for the protein? Briefly explain your 3 Lev -lle -Lev-ste-Cs cod jw Consider the situations in parts (f-h) independently f) A mutation occurs which results in the insertion of an extra G/C (top strand/bottom strand) base-pair immediately after base pair 11 (shown in bold). What effect will this insertion mutation have on the mRNA transcript and Codns, g) A different mutation results in the substitution of the T/A base pair at position 30 (shown in bold and underlined) with a G/C base pair. How would this mutation affect the sequence of the protein that is produced? h) A third mutation occurs which results in the substitution of the C/G base pair at position 42 (shown in bold italics) to a T/A base pair. How would this mutation affect the sequence of the protein that is produced?

Explanation / Answer

Please find the answers below:

The sequence of the original DNA can be found as below:

5' GTG TCC GTC TAA TAT TGT GAG ATG TTA TAT CC GCC GTC AAC ACC ATC 3'

Answer part g) If the mutation causes change in T/A to G/C at position 30, the new sequence would become:

5' GTG TCC GTC TAA TAT TGT GAG ATG TTA TAG CC GCC GTC AAC ACC ATC 3'

As an effect, the amino acid encoded from this 30th codon will not change from original isoleucine since both, AUA and AUC encode for isoleucine. Thus, this change will cause a silent mutation.

Answer part h) If the mutation causes change from C/G base pare at position 42 to T/A, the sequence would be:

5' GTG TCC GTC TAA TAT TGT GAG ATG TTA TAT CC GCC GTC AAT ACC ATC 3'

As an effect, the amino acid encoded from this 42nd codon will be same i.e. leucine in both cases since codons UUG and UUA both encode for amino acids leucine.

Thus, this too shall be a silent mutation with no effect on the protein.

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