Question

Under which of the following conditions will there be no change in the reading frame of following mRNA? 5' AACAGCGGUGCUAUU 3'

• A. Insertion of G at 5th position
• B. Deletion of G from 5th position
• C. Insertion of A and G at 4th and 5th positions respectively
• D. Deletion of GGU from 7th, 8th and 9th positions

Answer 1

The Correct Option is D

To determine under which condition there will be no change in the reading frame of the given mRNA sequence, we must consider the effect of insertion or deletion of nucleotides on the reading frame.

The mRNA sequence given is: 5' \, \text{AACAGCGGUGCUAUU} \, 3'.

The reading frame refers to the way nucleotides are grouped into codons, each consisting of three nucleotides. Altering this grouping by inserting or deleting nucleotides can lead to a frameshift mutation unless the number of nucleotides inserted or deleted is a multiple of three.

Let us evaluate each option:

1. Insertion of G at the 5th position: Inserting a single nucleotide will disrupt the triplet codon reading frame, causing a frameshift. Hence, this option affects the reading frame.
2. Deletion of G from the 5th position: Removing a single nucleotide also disrupts the triplet reading frame, thus causing a frameshift. This option does affect the reading frame.
3. Insertion of A and G at the 4th and 5th positions respectively: Inserting two nucleotides will not maintain the reading frame because two is not a multiple of three, causing a frameshift. Therefore, this option affects the reading frame.
4. Deletion of GGU from 7th, 8th, and 9th positions: Removing exactly three nucleotides (one full codon) does not change the overall reading frame because it still maintains the triplet codon structure. Thus, this option does not cause a frameshift and maintains the reading frame.

Therefore, the correct choice is: Deletion of GGU from 7th, 8th, and 9th positions, as this action does not cause a change in the reading frame.