Which codon is universally recognized as the start codon in bacteria?

Which codon is universally recognized as the start codon in bacteria?

• A. GUG
• B. UAG
• C. UGA
• D. AUG

Answer: (C)

The main concept is how the ribosome knows where to begin translating a gene. In bacteria, the standard start signal is AUG. When AUG is encountered, the ribosome recruits the initiator tRNA carrying formylmethionine (tRNA^fMet) and sets the reading frame so the new polypeptide begins with Met. This AUG start codon is recognized consistently across bacteria, which is why it’s considered the universal start signal. There can be rare cases where alternative codons like GUG initiate translation, but these are exceptions and not universal, so they don’t replace AUG as the standard start. In contrast, codons like UGA and UAG do not start translation; they signal termination. Hence AUG is the correct choice because it reliably directs the start of protein synthesis in bacteria.

The main concept is how the ribosome knows where to begin translating a gene. In bacteria, the standard start signal is AUG. When AUG is encountered, the ribosome recruits the initiator tRNA carrying formylmethionine (tRNA^fMet) and sets the reading frame so the new polypeptide begins with Met. This AUG start codon is recognized consistently across bacteria, which is why it’s considered the universal start signal.

There can be rare cases where alternative codons like GUG initiate translation, but these are exceptions and not universal, so they don’t replace AUG as the standard start. In contrast, codons like UGA and UAG do not start translation; they signal termination. Hence AUG is the correct choice because it reliably directs the start of protein synthesis in bacteria.