Question

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

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

Answer 1

The correct option is A Deletion of GGU from 7th, 8th and 9th positions

A sequence of three consecutive nucleotides on mRNA that are read as codons specifying amino acids is called a reading frame.

The reading frame of the RNA
5' AACAGCGGUGCUAUU 3' will not change by deletion of GGU, i.e. three nucleotides.

As each codon is made up of three consecutive nucleotides, deletion or insertion of three or multiples of three nucleotides will not alter the reading frame and only cause minimal changes.

However, insertion or deletion of one or two nucleotides will alter the whole reading frame from the point of insertion or deletion leading to frame-shift mutation.