Question

An mRNA sequence reads: GAA/GCU/AUA/CUA/UGU. What would the effect on the amino acid be if the second codon read GCA instead, and the third codon read AAU ?

A) Silent mutation on both, no changes whatsoever.
B) Silent mutation on second codon, third amino acid changed from PHE to STOP
C) Silent mutation on AAU only. Third amino acid is now HIS
D) Silent mutation on second codon, third amino acid changed from ILE to ASN.

Answer 1

D) Silent mutation on second codon, third amino acid changed from ILE to ASN.

Step-by-step explanation:

Silent mutations are usually point mutation where you change one nucleotide. Since, the nucleotide changed is the third position, it does not affect the protein being manufactured (it will still put the amino acid Ala) [look up the codon redundancy on youtub.e to understand how awesome nature is!]

On the other hand, the other mutation introduced is Missense mutation where a different Amino acid is added due to change in codon (goes from ILE to ASN).