Question

While working with cultured yeast cells, the scientist unknowingly treated the cells with a mutagen that although rare, causes deletion or insertion of individual bases in DNA. Subsequently, the scientist isolated and cultured a single cell from this group and noticed that the progeny of this cell were not producing a certain protein and this was having an effect on their viability (even though mayflies are so cool). The mutation would be most harmful to the cells if it resulted in ______.

a) a single nucleotide in the middle of the intron
b) a single nucleotide deletion near the end of the coding sequence
c) a single nucleotide insertion near the start of the coding sequence
d) substitution of a base pair
e) deletion of a triplet near the middle of the gene

Answer 1

The most harmful mutation is a single nucleotide insertion near the start of the coding sequence, which leads to a frameshift and can significantly alter or terminate the protein, possibly leading to conditions like cystic fibrosis. c) a single nucleotide insertion near the start of the coding sequence

Step-by-step explanation:

The mutation that would be most harmful to cells if it resulted in a single nucleotide insertion near the start of the coding sequence. This is because such a mutation causes a frameshift, altering the way the ribosomes read the mRNA during protein synthesis. Because codons are read in groups of three nucleotides, an insertion that is not a multiple of three will shift the reading frame and change the sequence of amino acids from that point onward. This can lead to the production of a nonfunctional protein or even trigger a premature stop codon, terminating protein synthesis too early. Examples of diseases caused by such mutations include cystic fibrosis and cat cry syndrome.

An insertion or deletion in a gene's coding sequence is far more consequential than a single nucleotide change in the middle of an intron, near the end of a coding sequence, or a base pair substitution. In contrast, deletion of a triplet may not cause a frameshift but could still be harmful if it removes a crucial amino acid from the protein.