"According to Karp, the RNA polymerase is capable of adding 20 to 50 nucleotides per second to the growing mRNA chain. Electron microscope images suggest that there can be over a hundred RNA polymerases operating simultaneously. So the cell nucleus is like a programmed factory for mRNA with over 100 parallel assembly stations. Each station can build a 400 unit mRNA chain in 10 to 20 seconds."