Translation happens in the cytoplasm of the cell on ribosomes, where the genetic instructions carried by mRNA are decoded and used to assemble amino acids into proteins. In eukaryotic cells, mRNA molecules need to exit the nucleus and move to the cytoplasm where ribosomes are present for translation to occur. In contrast, in prokaryotic organisms, ribosomes can start attaching to mRNA as it's being transcribed. Thus, translation begins at the 5' end of the mRNA while the 3' end is still attached to DNA.