Which event is the first step in the initiation process?

Which event is the first step in the initiation process?

• A. Binding of initiator tRNA to small subunit
• B. Attachment of large subunit
• C. Detection of start codon
• D. Binding of small subunit with tRNA to mRNA

Answer: (A)

In translation initiation, the first move is to form the initiation complex on the small ribosomal subunit by loading the initiator tRNA onto it. This tRNA, carrying the first amino acid, has the special role of recognizing the start codon and positioning itself in the P site, with initiation factors guiding the process. This step sets the precise reading frame and creates the ready platform for the mRNA to align so its start signal can pair with the anticodon. Only after this initiator tRNA is in place does the mRNA bind to the small subunit to position the start codon, and then the large subunit joins to form the complete ribosome and begin elongation. So, the earliest action is binding of the initiator tRNA to the small subunit. The other steps—attachment of the large subunit, start-codon detection, and the small subunit–tRNA–mRNA association—occur later in the sequence.

In translation initiation, the first move is to form the initiation complex on the small ribosomal subunit by loading the initiator tRNA onto it. This tRNA, carrying the first amino acid, has the special role of recognizing the start codon and positioning itself in the P site, with initiation factors guiding the process. This step sets the precise reading frame and creates the ready platform for the mRNA to align so its start signal can pair with the anticodon. Only after this initiator tRNA is in place does the mRNA bind to the small subunit to position the start codon, and then the large subunit joins to form the complete ribosome and begin elongation. So, the earliest action is binding of the initiator tRNA to the small subunit. The other steps—attachment of the large subunit, start-codon detection, and the small subunit–tRNA–mRNA association—occur later in the sequence.