How does the eukaryotic initiation complex locate the true start codon?

The initiation complex moves the small ribosomal subunit through the 5 UTR, scanning for the start AUG.

Explanation:

Eukaryotic translation is the process by which mRNA is translated into proteins in eukaryotes. It has three stages: initiation, elongation and termination.

Eukaryotic initiation complex is formed in initiation stage. It forms when the small ribosomal sub unit (40s) along with some eukaryotic initiation factors (eIF1, eIF3 etc.) recruits the initiator tRNA. The initiator tRNA has anticodon CAU which corresponds to first codon AUG on mRNA and carries methionine amino acid.

The whole initiation complex binds to the 5' end of mRNA. It begins to scan it from 5' UTR (untranslated region) to 3' end until the start codon is encountered. Once it is encountered, translation process finally begins with the first amino acid being methionine.