RNA polymerase II produces all the cell’s mRNA. Two other polymerases produce rRNA  (ribosomal RNA) and tRNA (transfer RNA).  RNA polymerase needs several extra proteins, or initiation factors, to function. These initiation factors must be added in the correct sequence to the origin point. The total number of amino acids involved in these initiation proteins is about 20,000, which is quite a load to place on the DNA molecule! Once transcription begins, the initiation factors are discarded. The copying process involves more or less the same proteins and requirements as for DNA replication. The product of transcription is a pre-mRNA molecule. Spliceosomes then cut out the introns to produce a finished mRNA molecule. This molecule, now provided with a suitable signaling molecule, is then able to move through the nuclear pore complex into the cytoplasm. It then proceeds to a ribosome which reads the nucleotide sequence and, with the aid of tRNA, puts together a new protein molecule as mandated by the information in the DNA.

Related Resources

• The Central Dogma: DNA to Proteins (YouTube, 11 min). Animated illustration of how complex the process is to copy information from the DNA into RNA and then to translate that into a protein. The “machines” illustrate the process.  Highly recommended!