Q.Describe the role of tRNA as an adapter molecule during translation. What are the anticodon and the amino acid-binding site of a tRNA molecule, and how does aminoacyl-tRNA synthetase contribute to this process?

AUG is the universal start codon that initiates translation and codes for methionine.

Working

In the standard genetic code, translation of an mRNA into a polypeptide always begins at a specific triplet codon called the initiation (start) codon, which is AUG. This codon is recognised by the initiator tRNA carrying the amino acid methionine (or N-formylmethionine, fMet, in prokaryotes), which is placed as the first amino acid of the growing polypeptide chain, setting the reading frame for all subsequent codons.

The other options are not start codons: UUU codes for the amino acid phenylalanine within an ongoing reading frame, while UAG and UGA are two of the three stop (termination) codons (along with UAA) that signal the ribosome to end translation and release the completed polypeptide -- they do not code for any amino acid.

Translation is the process of converting the mRNA nucleotide sequence into a polypeptide's amino acid sequence.

Gene expression proceeds in two major steps: transcription, in which the DNA sequence of a gene is copied into a complementary mRNA molecule, followed by translation, in which that mRNA is read at the ribosome in successive triplets (codons), each specifying a particular amino acid (or a stop signal) according to the genetic code; transfer RNAs bring the correct amino acids to match each codon, and these are joined by peptide bonds to build the polypeptide chain. Transcription (option b) is the earlier, DNA-to-mRNA step, not mRNA-to-protein, so it is incorrect here. A nonsense codon is simply a stop codon that terminates translation, not the whole process, and 'genetic code' refers to the set of rules relating codons to amino acids, not the process of decoding itself -- so 'translation' is the precise term for what is described.