Question

*Template Strand of DNA 3. The following shows the first portion of a DNA strand of a gene that is 2,500 base pairs long. AUG TACȚTCCCGGAGCCC--- TAAG LLL ODRAL a. What is the amino acid sequence encoded for by this strand starting with the T nucleotide on the left? Met b. Give an example of a synonymous substitution (a silent mutation) that could occur in the second codon of the DNA strand. c. Give an example of a nonsense mutation that could occur in the second codon of the DNA strand. (side note - for practice, make sure you can come up with a missense mutation) d. Rank the following occurrences in terms of their effect on the phenotype produced by this gene (0 - no change; 1 small change: 2 large or catastrophic change). You may use the same number multiple times, or not at all. A mutation changing a T to a C at location 1 (meaning #1 pointing to DNA strand at top of page) A deletion of the Tat location 2 An insertion of a TTT nucleotide triplet at location 3

Answer 1

DNA       TAC TTC CCG GAG CCC
mRNA     AUG AAG GGC CUC GGG

AMINOACID Met-Lys-Gly-Leu-GLy

B. Second codon TTC to TTT
mRNA          AAG to AAA
               Lys to Lys
The 3rd base pair in second codon changes from C to T leads to silent mutation.

C. Second codon TTC to ATC
mRNA                AAG to UAG
                  Lys to Stop codon
The 1st base pair in second codon changes from T to A leads to nonsense mutation.

D.       TAC to CAC
mRNA      AUG to GUG
Aminoacid Met to Val

This result in small change 1.

Deletion of T leads to frame shift mutation makes a large change 2.

TTT leads to small change 1.