Re: Why does mRNA need a cap and a tail?

Through experimenting with injected RNAs in eukaryotes (cells with a nucleus), researchers have found their messenger, or mRNAs (which are a message created from the DNA in a cell) often have a special chemical cap at one end and a string of adenosine residues as a tail. The cap is at the beginning, called the 5' (five prime) end. The tail is at the end, called the 3' (three prime) end. Both the cap and the tail are added after the RNA is made.

For the most part, caps and tails are added to RNA molecules that will be used to make protein molecules (mRNA). The cap and tail are added to the RNA as a sort of a tag to tell the cell to use that RNA to make a protein. (There are some RNA molecules that do other things in the cell than making proteins.) Scientists have found that RNAs without a cap or tail tend to be degraded before they can be used to make a protein.

Because caps and tails are good indications of RNA's that will become proteins, many scientists purify this group of RNA from a cell. By analyzing the sequence of the different molecules, the scientists can tell what proteins will be made by the cell.