How does translation initiation differ between eukaryotes and prokaryotes?

How does translation initiation differ between eukaryotes and prokaryotes?

• A. In prokaryotes, initiation uses a Shine-Dalgarno sequence; in eukaryotes, initiation typically involves scanning from the 5' cap to the start codon.
• B. In prokaryotes, initiation requires a poly-A tail; in eukaryotes, initiation uses Shine-Dalgarno sequence.
• C. Prokaryotes do not use initiator tRNA; eukaryotes do.
• D. Translation initiation is identical in both, with no differences.

Answer: (A)

Translation initiation hinges on how the ribosome is guided to the start codon. In prokaryotes, the mRNA carries a Shine-Dalgarno sequence that base-pairs with the 16S rRNA of the small ribosomal subunit. This interaction positions the ribosome so the start codon sits in the P site, allowing translation to begin directly without a scanning step; this mechanism also explains why many prokaryotic mRNAs can encode more than one protein (polycistronic). The initiator amino acid is formylmethionine in bacteria. In eukaryotes, initiation relies on recognition of a 5' cap by eukaryotic initiation factors, then the ribosome scans downstream through the 5' UTR until it encounters an AUG in a favorable Kozak context, at which point translation starts; the initiator tRNA brings methionine (not formylated). The cap-dependent scanning scheme and reliance on the Kozak sequence make eukaryotic initiation distinct from the Shine-Dalgarno–dependent mechanism in bacteria.

Translation initiation hinges on how the ribosome is guided to the start codon. In prokaryotes, the mRNA carries a Shine-Dalgarno sequence that base-pairs with the 16S rRNA of the small ribosomal subunit. This interaction positions the ribosome so the start codon sits in the P site, allowing translation to begin directly without a scanning step; this mechanism also explains why many prokaryotic mRNAs can encode more than one protein (polycistronic). The initiator amino acid is formylmethionine in bacteria. In eukaryotes, initiation relies on recognition of a 5' cap by eukaryotic initiation factors, then the ribosome scans downstream through the 5' UTR until it encounters an AUG in a favorable Kozak context, at which point translation starts; the initiator tRNA brings methionine (not formylated). The cap-dependent scanning scheme and reliance on the Kozak sequence make eukaryotic initiation distinct from the Shine-Dalgarno–dependent mechanism in bacteria.