Question

How many amino acids will be coded by the sequence if the 14th base of given mRNA converted to G?
5’AUG UUU CUC UAG CCG 3'
A. Three
B. Five
C. Four
D. Two

Answer 1

Genetic code is an inter-relationship between nucleotide sequence of DNA or mRNA and amino acid sequence containing information for one amino acid and consists of three nucleotides. George Gamow, a physicist coined the term genetic code.

Complete answer:
There are two types of genetic code. The genetic code can be expressed as an RNA codon or a DNA codon.
A genetic code can be defined as the word that defines the amino acid sequence in protein synthesis, or as the exact nucleotide sequence of DNA, which is read as a three-letter codon. In other words, a genetic code is a set of rules by which information encoded in genetic material (DNA or RNA sequences) is converted by living cells into proteins (amino acid sequences).
Salient features of genetic code
Triplet code-That is, a set of three nucleotide bases is a codon.
Non-ambiguous and specific codons -One codon codes for only one amino acid.
Comma less nature-There are no commas in the genetic code, so no punctuation marks between the two codons are required.
Degeneracy of code-Some amino acids are coded by more than one codon hence code is degenerate.
Universal code-The genetic code was developed using an in vitro microbial system, but there is no doubt that it is universal for all groups of microbes. In 1967, Nirenberg and his team proved the universality of the code.
Non-overlapping codon-Genetic codes do not overlap, so the same letter is not involved in the formation of more than one codon.
Now coming to the question
We know that AUG is a start codon and also codes for methionine.
UUU codes for phenylalanine.
CUC codes for leucine.
UAG is a stop codon also known as Nonsense codon because it does nodes for any amino acid and translation will terminate here so if at fourteenth position we change the base from to G it does not affect translation or the number of amino acids coded.

So the correct answer is (A).

Note:

GUG is an ambiguous codon , It normally codes for valine but at initiating position , codes for methionine.
Some amino acids like leucine, serine arginine are coded by six codons.
Some amino acids like proline, alanine, valine and threonine are coded by four codons.
AUG and UGG are degenerate codons.
AUG has dual function, It codes for methionine and also acts as initiator codon.
UAA, UAG and UGA act as stop codons. They do not code for any amino acid hence called stop codons.