Final answer:
The ends of mRNA are not translated because they contain regulatory regions but not coding regions. The open reading frame is the part of mRNA that is translated into protein. Differences in translation between prokaryotes and eukaryotes are attributed to cellular organization and mRNA processing.
Step-by-step explanation:
The ends of prokaryotic and eukaryotic mRNA's are not translated because they contain untranslated regions (UTRs) that are necessary for the regulation of translation rather than coding for amino acids. The 5' UTR in prokaryotic mRNA often includes a ribosome binding site which is essential for the initiation of translation. On the other hand, eukaryotic mRNA has a 5' cap and a 3' poly-A tail that are not translated but are important for stability, export out of the nucleus, and the initiation of translation. The open reading frame (ORF) is the part of the mRNA that is translated into protein and is flanked by the start codon and the stop codon.
In prokaryotes, translation can commence even before transcription is complete, due to the absence of a nucleus and the proximity of ribosomes to the nascent mRNA transcript. Conversely, eukaryotic mRNA must undergo several processing steps, including splicing of introns, before it can be translated in the cytoplasm. These differences highlight the distinction in cellular organization and mRNA handling between prokaryotes and eukaryotes. Termination of translation occurs when a stop codon is reached, prompting the recruitment of release factors that disassemble the translation complex, releasing the newly synthesized polypeptide.