Final answer:
During initiation of translation in biology, the large ribosomal subunit binds to the small ribosomal subunit, forming a complete ribosome.
Step-by-step explanation:
The last thing that happens during initiation of translation is that the large ribosomal subunit comes down and clicks into place with the small ribosomal subunit, forming a complete ribosome. This occurs after the small subunit binds to the mRNA and scans until it reaches the start codon, and the initiator tRNA binds to the start codon. Finally, the large subunit binds, aligning the initiator tRNA in the P site.