Final answer:
In prokaryotic cells, multiple ribosomes attach to the 5' end of an mRNA molecule and begin translation while transcription is still ongoing at the 3' end, a process facilitated by polyribosomes. In contrast, eukaryotic cells separate transcription and translation, with translation commencing only after mRNA processing and export from the nucleus.
Step-by-step explanation:
In prokaryotic cells, transcription and translation are simultaneous; so multiple ribosomes may be attached to the 5' end of the mRNA while transcription is still taking place at the 3' end. This highly efficient process is facilitated by the formation of structures known as polyribosomes or polysomes, which consist of multiple ribosomes that simultaneously translate a single mRNA molecule. This concurrent activity allows prokaryotic cells to respond very quickly to environmental signals requiring new proteins. Unlike prokaryotes, eukaryotic cells do not exhibit simultaneous transcription and translation; instead, transcription occurs in the nucleus, and once complete, the mRNA must be modified and transported out of the nucleus for translation to occur in the cytoplasm. This separation of the two processes in eukaryotes means that polysomes can only form after the mRNA has been processed and exported to the cytoplasm.