Question

The first step of translation begins when __________.

the initiator amino-acyl-tRNA binds to the start codon on the mRNA at the A site of the ribosome
the 30S ribosomal subunit combines with the 50S ribosomal subunit, enclosing the mRNA
the tmRNA binds to the A site on the ribosome to initiate translation
the ribosome binding site (RBS) on the mRNA binds to the 16S rRNA to begin the formation of the initiation complex

Answer 1

Translation initiation begins with the small ribosomal subunit binding to the mRNA and the initiator tRNA recognizing and attaching to the start codon, followed by the large ribosomal subunit joining to form the initiation complex.

Step-by-step explanation:

The first step of translation begins when the initiator tRNA anticodon recognizes the start codon on mRNA. This is typically an AUG codon, which codes for methionine in eukaryotes or N-formyl-methionine in prokaryotes. The initiator tRNA carries this specific amino acid and binds to the P site of the small ribosomal subunit.

Then, initiation factors assist as the small subunit binds to the mRNA and scans to find the correct start codon. Upon locating the AUG, the initiator tRNA establishes a hydrogen bond with the start codon. After this pairing, the large ribosomal subunit joins, which completes the initiation complex formation essential for translation to proceed.