What is the start codon and amino acid it encodes in most organisms?

What is the start codon and amino acid it encodes in most organisms?

• A. UAA — stop
• B. AUG — methionine
• C. GUG — valine
• D. UGG — tryptophan

Answer: (B)

The start of translation is marked by a codon that both signals where to begin and designates the first amino acid. In almost all organisms, that codon is AUG, and the initiator tRNA brings methionine to the ribosome to start the polypeptide chain. In bacteria this initiator methionine is often formylated, but the codon responsible is still AUG and the first amino acid is methionine. The other options point to a stop signal or to codons that normally encode different amino acids, so they don’t serve as the universal start signal in most organisms.

The start of translation is marked by a codon that both signals where to begin and designates the first amino acid. In almost all organisms, that codon is AUG, and the initiator tRNA brings methionine to the ribosome to start the polypeptide chain. In bacteria this initiator methionine is often formylated, but the codon responsible is still AUG and the first amino acid is methionine. The other options point to a stop signal or to codons that normally encode different amino acids, so they don’t serve as the universal start signal in most organisms.