For genes encoded in the eukaryotic nucleus, why are transcription and translation usually separated in space and time?

Core Concept

Nuclear transcription occurs inside the nucleus, where the primary transcript can be capped, processed, and packaged before export through nuclear pores. Cytosolic ribosomes translate the exported mRNA. This spatial separation applies to nuclear gene expression; mitochondria and chloroplasts have their own gene-expression systems and should not be folded into the absolute statement that no eukaryotic transcription and translation can be coupled.