Final answer:
Eukaryotic mRNA uses a 5' cap structure for the initiation complex to attach, which includes the 40S small ribosomal subunit and initiation factors, in contrast to the Shine-Dalgarno sequence used by prokaryotes. The 7-methylguanosine cap is recognized, then the complex scans for the start codon to begin translation.
Step-by-step explanation:
Eukaryotic mRNA does not have an Shine-Dalgarno sequence that facilitates attachment of the small subunit; instead, it utilizes a 5' cap structure. In eukaryotes, the initiation complex, including initiation factors (IFs), the 40S small ribosomal subunit, and the charged initiator tRNA, which in eukaryotes carries methionine (Met-tRNAi), binds to the mRNA. The key difference is that in eukaryotes, the complex recognizes the 7-methylguanosine cap at the 5' end of the mRNA. Once bound to the cap, the complex scans the mRNA in the 5' to 3' direction until it locates the AUG start codon, following which the 60S ribosomal subunit joins to form the complete initiation complex for protein synthesis.