messenger RNA
Messenger RNA, or mRNA, is the working copy of a gene — the memo that carries an order from the boss (DNA in the nucleus) out to the factory floor (the ribosome) where the actual product, a protein, gets built. It is a temporary, disposable intermediary, not the permanent record.
An mRNA is a single strand of RNA whose sequence of bases spells out, in three-letter codons, the order of amino acids for one or more proteins. Between the message and DNA sits a faithful chemical relationship: the mRNA was copied from a gene by transcription and now waits to be read by translation.
In eukaryotes a finished mRNA carries extra features that mark it as ready and protect it: a cap at the front, a tail of many A's at the back, and untranslated regions that help control how often and how long it is used. Because mRNA is short-lived, the cell can switch a protein on or off quickly by making more or less of its message.
Some vaccines deliver a lab-made mRNA encoding one viral protein; the recipient's own ribosomes translate it briefly, then the mRNA degrades — a vivid demonstration of mRNA as a transient message.
mRNA is information to be read, then discarded — never stored permanently.