Question

a) Three nucleotides are inserted into a protein-encoding gene. The insertion occurs such that the mRNA transcript has an additional 3 bases (NOT a stop) right next to the stop codon (on the 5’ side). Which of the following will be the result?

b) Which of the following are consequences of encoding each amino acid using 3 nucleotides in the Genetic Code? (mre than one)

A. There are three different reading frames in a single-stranded mRNA
B. tRNA anticodons contain 3 nucleotides
C. There are three types of substitutions in protein coding regions (silent, missense, nonsense)
D. Amino acids can be encoded by more than one codon
E. There are three different stop codons
F. Insertion/deletion of non-multiples of 3 bases in ORFs creates a frameshift

Answer 1

a) Insertion of 3 additional bases into a protein-encoding gene right next to the stop codon (on the 5’ side) will result in insertional mutation. The reading frame remains intact after the insertion and translation will most likely run to completion if the inserted nucleotides do not code for a stop codon. However, because of the inserted nucleotides, the finished protein will contain, depending on the size of the insertion, multiple new amino acids that may affect the function of the protein.

b) Options A, D, E and F are correct; There are three reading frames that can be read in this 5'→3' direction, each beginning from a different nucleotide in a triplet. Genetic codon is degenerate and contains wobble base, hence why amino acids can be coded b ymore than one codon.  A frameshift mutation is alteration in the normal reading frame of a gene, if the number of inserted nucleotides is not divisible by three, i.e., the number of nucleotides per codon.