Question

what does “coupled” in prokaryotic gene expression mean in transcription and translation. What are two consequnces for the coupled transcription and translation?

Answer 1

The term "coupled" In prokaryotic gene expression means that In a prokaryotic cell,  translation begins while the mRNA is still being synthesized. In a eukaryotic cells ,transcription takes place  in the nucleus, and translation occurs in the cytoplasm. Bacteria do not have a membrane bound nucleus which separates DNA from ribosomes, thus there is no barrier for immediate translation in case of bacteria. This can not happen in eukaryotic cells, because eukaryotic RNAs are comprised of introns and exons which must be edited before translation can begin. Therefore in eukaryotes, while transcription takes place in the nucleus, translation occurs in the cytoplasm. Transcription and translation are spatially and temporally isolated in case of eukaryotic cells.

However, bacteria  have a comparatively less complicated genome and they do not  need to separate these processes.Bacteria are having a plethora of advantages as a consequence of coupling these processes. One advantage is the energy needed for translation and trancription, the energy needed to complete the process of transcription could be provided by the expenditure of unstable nucleotidetriphosphates during the process of translation and the other  advantage to coupled transcription and translation is that it provides a unique  mechanism for the regulation of gene expression in prokaryotes. For example the operation of Lac-operon in prokaryotes.