(4 pts) Nonsense mutations are mutations that introduce a STOP codon in place of

Question

(4 pts) Nonsense mutations are mutations that introduce a STOP codon in place of a sense codon, and result in premature termination of translation. These mutations are not as rare as you might think. For example, there are 8 different sense codons that can be changed to the stop codon UAG by a single point mutation (base change) 4. Using the codon table in the textbook, list these 8 sense codons (and their corresponding amino acid) Consider the following introduction of a nonsense mutation into the provided wild type sequence. Transcribe both the wild type and mutant sequence into mRNA and then translate each into its respective polypeptide. I WANT TO SEE POLARITY FOR ALL MOLECULES! Nonsense , mutation 5'-AT 5 -ATGCcGGTCCAGCTT-3 GccGGTCTAGCTT-3' template3'-TACGGCCAGGTCGAA-5' 3 '-TACGGCCAGATCGAA-5' *- template What is a nonsense suppressor mutation? Describe how a mutation in a tRNA for serine with the anticodon sequence 3'-AGC-5' could correct for the above described nonsense mutation. How would this affect the final translated protein in relation to the normal protein? Be specific as to the exact mutational change in the protein and speculate as to whether you think this might be a significant change in the function of the protein e.g. consider the biochemical properties of the amino acids.

Explanation / Answer

Eight Codons are

UUA, UUG Both codes for Leucine

UCA, UCG both codes for serine

UAU, UAC both codes for Tyrosine

UGU, UGC both codes for cysteine

Wild-type -

ATG CCG GCT CAG CTT

mRNA 5' AUG CCG GCU CAG CUU 3'

Protein N-terminal -  M P A Q L- C-terminal

Mutant -

ATG CCG GCT TAG CTT

mRNA 5' AUG CCG GCU UAG CUU 3'

Protein N-terminal -  M P A Stop codon

Nonsense suppressor mutation is a mutation in tRNA such that it recognizes the nonsense codon or stop codon as the amino acid coding codon in the mRNA template.  

Mutation in the anticodon loop of tRNA of serine in which 3' AGC 5' is mutated into 3' AUC 5' will allow the ribosome to add serine on the place of nonsense codon.

Now the peptide will have the following sequence

Protein N-terminal -  M P A S L - C-terminal

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