Transcription is the first half of protein biosynthesis whereby a sequence of DNA is converted into a complementary strand of mRNA. The process is different in prokaryotic cells versus eukaryotic cells. The biggest difference is that since prokaryotic cells don't have a nucleus, their DNA is contained in the cytoplasm and transcription takes place there. In eukaryotic cells, transcription takes place in the nucleus and then the resulting mRNA is transported to the cytoplasm. Also, in prokaryotic cells transcription and translation can take place simultaneously since both occur in the cytoplasm. In eukaryotic cells they must take place sequentially since they do not occur in the same part of the cell.