Question

In mRNA, AUG is the initiation codon and UAA, UAG, and UGA are termination codons. Thus polypeptides cannot be synthesized beyond any of these triplets to the end of the mRNA. Then which of the following mRNA can be translated completely?
a. AUG UUC UCC UGG UAA UAU
b. AUG UUC UCC UGA UGG UAU
c. AUC ACG UAU UUC UGA CUC
d. AUG UAU UUC UGC CUC UAG

Answer 1

Hint: The process of conversion of DNA-mRNA-protein is called the ‘central dogma’ of inheritance biology. The genetic material (DNA) synthesizes proteins through messenger RNA (mRNA) with the help of transcription and translation. The product of translation is protein. Proteins complex molecules made up of amino acid chains. Proteins look after the wear and tear of the body tissues.

Complete answer:
- Transcription is a process of formation of single stranded messenger RNA (mRNA) from a template strand of DNA, in the nucleus. The mRNA is complementary to the template DNA.
- When the mRNA is formed, it comes out of the nucleus to the cytoplasm. There, the ribosomes hold the mRNA and make chains of amino acids by reading its code language, with the help of tRNA
- This code language that ribosome translates is called the triplet codons.
- Triplet codons are a group of three bases in the mRNA that code for a particular amino acid.
- There are 20 total amino acids. Each amino acid is a unique triplet codon.
- AUG is a triplet codon that codes for amino acid methionine. It is a start codon, i.e. the translation process starts only when the tRNA identifies the AUG code in the ribosomal subunit.
- The codons UAA, UAG, and UGA do not code for any of the 20 amino acids. They are the stop codons, i.e the process of translation stops here.
- tRNA has base sequences that are complementary to the codons (anticodons), using which the tRNA binds to triplet codon and one amino acid is added to the protein chain.
- Here, the option (d) has sequence AUG UAU UUC UGC CUC UAG; wherein, the translation process will start at AUG (start codon) and end at UAG (stop codon) thus the complete sequence will be translated.

Hence, the correct answer is option (D).

Note: A scientist of Indian origin, Dr. Har Govind Khurana played a major role in the discovery of triplet codons for 20 amino acids. He and two more scientists were awarded the Nobel prize in 1968. The genetic code is universal in nature. That means it is applicable to all the living beings present on Earth.