Final answer:
In prokaryotes, ribosomes can attach to the mRNA and begin translation before transcription is complete due to the lack of a nuclear membrane and the simultaneous occurrence of both processes in the cytoplasm.
Step-by-step explanation:
In prokaryotes, ribosomes can attach to the mRNA and begin translation even though transcription has not been completed. In these organisms, transcription and translation are closely coupled processes, due to the lack of a nuclear membrane, allowing the processes to occur concurrently in the cytoplasm. Ribosomes bind to the mRNA molecule that is still being transcribed and start synthesizing proteins. This ability for concurrent transcription and translation is due to the colinear flow of processes in the same 5' to 3' direction within the prokaryotic cell. In contrast, eukaryotes undergå pre-mRNA modifications such as 5' capping and the addition of a poly-A tail, and transcription occurs within the nucleus. Therefore, ribosomes must wait for the complete mRNA transcript to be exported to the cytoplasm before translation can start.