Final answer:
The Shine-Dalgarno sequence signals the ribosome where to start protein synthesis in prokaryotes by aligning the mRNA with the 30S ribosomal subunit. In eukaryotes, a cap-binding mechanism involving the 7-methylguanosine cap is used instead, with additional rules known as Kozak's rules to locate the start codon.
Step-by-step explanation:
The ribosome binding site, known as the Shine-Dalgarno sequence (AGGAGG), plays a crucial role in the process of protein synthesis in prokaryotes. This specific sequence on the messenger RNA (mRNA) is found just upstream of the start codon AUG. Its primary function is to align the mRNA with the 30S subunit of the ribosome, ensuring that translation begins at the correct point. The Shine-Dalgarno sequence interacts specifically with the ribosomal RNA (rRNA) that comprises the small subunit of the ribosome. This interaction is vital for the initiation of protein synthesis because it positions the ribosome correctly, allowing the first aminoacyl-tRNA to bind at the start codon, thereby initiating the process of translation.
In contrast to prokaryotic translation initiation, eukaryotic cells employ a different mechanism. Instead of a Shine-Dalgarno sequence, the eukaryotic initiation complex recognizes the 7-methylguanosine cap at the 5' end of the mRNA. Eukaryotic initiation relies on cap-binding proteins and initiation factors to locate the start codon, which may not necessarily be the first AUG codon. The efficiency of translation in eukaryotes is influenced by Kozak's rules, which indicate that specific nucleotides surrounding the AUG codon determine its suitability as the start site for protein synthesis.