Q.Which of the following is the start codon?

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.

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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 h …