Question

Identify the sense codon from the following.
A. UGA
B. AUG
C. UAG
D. UAA

Answer 1

Hint: 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. The codons encoding amino acids are called sense codons. The genetic code contains sixty one sense codons encoding twenty amino acids.

Complete answer:
Genetic code is inter-relationship between nucleotide sequence of DNA or mRNA and amino acid sequence containing information for one amino acid and consists of three nucleotides or we can say that genetic code is a set of rules which states that information encoded in genetic material is converted by living cells into proteins. George Gamow, a physicist coined the term genetic code.
Let’s first look at the properties of genetic code
Triplet code-That is, a set of three nucleotide bases is a codon.
Non-ambiguous and specific codons -This means that one codon codes for only one amino acid.
Comma less nature- The genetic code contains no commas, 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 let’s come to the question
The codons encoding amino acids are called sense codons. The genetic code contains 61 sense codons encoding 20 amino acids. Example- AUG which codes for methionine.
Stop signals-UAA, UAG and UGA act as stop codons because the polypeptide chain is signalled by these three codons. They do not code for any amino acid hence called stop codons.

Hence the correct option is (B) AUG which is an example of sense codon and others are examples of non-sense codon.

Note: GUG is ambiguous codon , It generally codes for amino acid valine but at initiating position , It codes for methionine.
Some amino acids like leucine, serine and 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 two functions, It codes for methionine and also act as initiator codon.