Messenger RNA is the short-lived working copy that turns genes into proteins
Your DNA stays locked in the cell nucleus like a reference library, so cells make disposable copies of individual genes to carry out to the protein factories. These copies, called messenger RNA, were first imagined in a 1960 conversation between Sydney Brenner, Francis Crick and François Jacob.
Production starts when an enzyme, RNA polymerase, latches onto a starting signal on DNA and builds a matching single strand of RNA. One letter changes along the way: where DNA uses thymine, RNA uses uracil. A popular explanation for why DNA kept thymine is maintenance, because cytosine can decay spontaneously into uracil, so a genome that never normally contains uracil can treat any it finds as damage to fix.
In bacteria the fresh strand is ready at once, and ribosomes start reading it before copying even ends. Cells with a nucleus take longer. Their first draft is cut and spliced, removing stretches called introns and joining the useful exons. A modified guanine cap goes on the front, helping ribosomes recognise the molecule and shielding it from enzymes that chew up RNA, and a tail of roughly 200 to 250 adenine units is added to the back for protection and export. Occasionally the message is edited; in some human tissues, one change creates an early stop signal so a shorter protein is made.
Once in the cytoplasm, ribosomes read the message three letters at a time, each triplet or codon naming an amino acid, which transfer RNA delivers. Reading typically starts at AUG and halts at one of three stop codons nicknamed amber, ochre and opal. Sections before and after the coding part are not translated but influence how stable the molecule is, where it goes and how efficiently it is used.
Location matters too. Neurons ship certain messages out to dendrites so proteins can be made right beside active synapses, guided by address tags biologists call zip codes. Messenger RNA was demonstrated experimentally in two Nature papers in May 1961, and Jacob and Jacques Monod gave it its name.
Source: Messenger RNA
