Question

Given below is a sequence of the processed mRNA ready for translation
5' AUG CUA UAC UAA CUG CCA UGC UAG 3'
How many amino acids will present in the polypeptide chain corresponding to this mRNA?
a. 7
b. 8
c. 6
d. 3

Answer 1

The mRNA sequence given will be undergoing the process of translation i.e. synthesis of protein in which three types of RNA take part. Out of three the tRNA brings the amino acids and reads the genetic code. AUG is known as chain initiation codon and UAA is the stop codon. In the sequence given above UAA is present in fourth place. Hence only three amino acids will correspond to this mRNA.

Complete answer:
- DNA sends genetic information for translation by synthesizing mRNA. The genetic information is carried by four types of N- bases.
- A codon is the sequence of 3-N bases on mRNA that codes for particular amino acids and the set of all codons that specify 20 amino acids are card genetic code.
- AUG is the chain initiation codon as it starts the synthesis of the polypeptide chain. UAA causes the termination of protein synthesis hence also called termination codons.
- In the given mRNA sequence translation starts from the 5 ends as the AUG code is present and it also codes for methionine. As there are 8 codons present in the sequence but at the fourth UAA (termination codon) is present which will terminate the translation hence protein for only three amino acids will synthesize.

Hence, the correct answer is option (D).

Note: Wherever in the mRNA sequence the termination (means stop signal) codon is present it will terminate the process of translation there and UAA codon does not code for any amino acid. It is also known as a nonsense codon. Apart from UAA, UAG and UGA are also called the termination codons.