mRNA is called messenger RNA. It is involved with a cell's production of protein polypeptides. It helps bridge the two main stages of protein biosynthesis. mRNA is formed in the first step called transcription. In the nucleus, a DNA sequence is converted into a complementary sequence of mRNA. This RNA is called messenger because it then leaves the nucleus and travels to the ribosomes in the cell. Once there, the mRNA helps facilitate translation where its nucleotide sequence is used to build up a protein one amino acid at a time. After the protein is completed, the mRNA is no longer needed and is degraded by a variety of different mechanisms depending on the type of cell. The degraded nucleotides can then be used to make a new strand of mRNA for a new protein and start the process all over again.
The copying of a complementary messenger RNA strand on a DNA strand is called transcription. Transcription requires a template, activated precursors, a divalent metal ion, and RNA polymerase. Prokaryotic mRNAs are polycistronic and can initiate protein synthesis at internal positions. On the other hand eukaryote mRNAs are monocistronic. They have been described as containing only one initiatio site for polypeptide chain by Jacobson and Baltimore (1968), who suggested that in animal cells a single mRNA produces a single polypeptide chain (one-mRNA, one-polypeptide hypothesis). In some cases a polyprotein is produced, which later undergoes cleavage to form several proteins).