Question

Which of the following is a stop codon?
A. AUG, GUG, UUU
B. UGA, UAG, UAA
C. UUU, UAC, CUC
D. CUC, UAC, UAA

Answer 1

Hint: A stop codon terminates the protein translation. The stop codons are the nonsense codons that do not code for any amino acid.

Complete Answer:
- The cells synthesize protein by the process of Protein synthesis. It occurs in two steps.
Transcription- DNA is converted to tRNA by the enzymatic activity of RNA polymerase through the process of transcription.
- Translation- tRNA is converted into an amino acid chain. It takes place by the initiation of a polypeptide chain. The first codon is called the start codon which initiates the translation is AUG i.e methionine. The Amino acid chain synthesises till it reads the stop codons- UAA, UGA, UAG. Once the stop codon is transcribed, protein synthesis stops. The protein is translocated further to the target site.

Thus the correct answer is (B). UGA, UAG, UAA are called stop codons.

Additional Information: The genetic code is the set of rules in a living organism which translate the triplet nucleotide into amino acid sequence. The genetic code is similar in all organisms. 64 triplet codons codes for 20 amino acids.

Note: Translation occurs in ribosomes. During translation, the mRNA carries the information for the amino acid to be transcribed. The tRNA molecule carries the synthesised amino acid which reads 3 nucleotides at a time till it comes across any of the stop codons.