Note whether the following mutations are likely (based on their nature and locat

Question

Note whether the following mutations are likely (based on their nature and location) to result in either a significant to complete loss of protein function (SC); or a partial to negligible loss of protein function (PN). Fill in each blank with either “SC” or “PN”.

      A) Deletion of 2 base pairs just downstream of the start codon.
      B) Nonsense mutation in the second of fifteen exons.
      C) Transposon insertion in the 3’ UTR.
      D) Missense mutation in a region of the gene that is required for proper folding/function of the protein.
      E) Silent mutation in a region of a gene that contains a conserved domain.
      F) Deletion of 3 base pairs just upstream of the stop codon.
      G) Transversion in the first intron.
      H) Frameshift mutation in the middle of a gene.
      I) Temperature-sensitive mutation.
      J) Deletion of the promoter.

Explanation / Answer

Please find the answers below:

A) SC (The nucleotides located upto -35bp just before the start codon are absolutely necessary to be conserved for identification of the start site by RNA polymerase, hence any deviation in their sequence leads to failure of gene expression)

B) SC (A non-sense mutation in the second exon will be too early in the 15-exon long gene, hence a non-functional polypeptide will be transcribed or altogether no transcription would proceed)

C) SC (The 3' UTR is essentially required for identification of the start codon by RNA polymerase. If this sequence has been interrupted, no transcription takes place)

D) SC (A functional protein is formed after proper folding of the polypeptide, failure of which makes it futile in nature)

E) PN (A silent mutation does not bring about any biochemical change in the nature of amino acids)

F) PN (The length of the gene expressed in this case would be shortened by a single amino acid)

G) PN (Introns are not expressed in the genes, hence no change will occur)

H) SC (The frameshif mutation causes change in the entire reading frame of the gene, hence a significant change in the whole gene expression)

I) PN (The gene will be experessed but the extent of expression depends upon the change in temperature)

J) SC (failure of transcription leads to inability to express the gene)

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