Question

The following DNA non-template sequence (coding sequence) is transcribed from left to right. Use the sequence to determine the type of mutation and the type of base substitutions that apply to each scenario. Place only one statement for each scenario.
A T G T T A C G C C C A A G C
(A) An adenine subtituted for nucleotide 5
(B) A ganine subtituted for nucleotide 12
(C) An adenine subtituted for nucleotide 15

Answer 1

Answer:

(A) A transversion base substitution causing a missense mutation

(B) A transition base substitution causing a silent mutation

(C)  A transversion base substitution causing a silent mutation

Explanation:

There are two types of base substitutions, transversions and transitions. A transition is when the a purine base is substituted with another purine base or a pyrimidine base is substituted with a pyrimidine base (e.g. Purines - A to G; G to A;  Pyrimidines - C to T; T to C). A transversion occurs when a purine base is substituted with a pyrimidine base or a pyrimidine base is substituted with a purine base (e.g. A to T; C to A).

There are three main types of mutations, these are missense mutations, nonsense mutations and silent mutations. Missense mutations occur when a base is changed and the codon now codes for a different amino acid to before the mutation. Nonsense mutations occur when a base is changed and now the codon codes for a stop codon causing a premature stop of the translation process. Silent mutations occur when a base is changed but the new codon still codes for the same amino acid as before the mutation.