Translation initiation begins when the ribosome binds to mRNA and encounters which start codon?

Translation initiation begins when the ribosome binds to mRNA and encounters which start codon?

• A. UAA
• B. UGA
• C. UAG
• D. AUG

Answer: (D)

Translation initiation relies on a specific signal on the mRNA that tells the ribosome where to start reading the sequence. That signal is AUG, which codes for methionine and is recognized by the initiator tRNA carrying methionine (formylmethionine in bacteria). This start codon sets the reading frame and helps assemble the initiation complex so elongation can proceed. The other codons listed are stop codons (UAA, UGA, UAG); they signal termination of translation, not the start of it. Once AUG is found, the ribosome places the initiator tRNA in the P site and translation begins.

Translation initiation relies on a specific signal on the mRNA that tells the ribosome where to start reading the sequence. That signal is AUG, which codes for methionine and is recognized by the initiator tRNA carrying methionine (formylmethionine in bacteria). This start codon sets the reading frame and helps assemble the initiation complex so elongation can proceed. The other codons listed are stop codons (UAA, UGA, UAG); they signal termination of translation, not the start of it. Once AUG is found, the ribosome places the initiator tRNA in the P site and translation begins.