When does an amino acid chain become a protein?

The DNA molecule in the nucleus makes a copy of itself using RNA, this is Messenger RNA.

The Messenger RNA travel to a Ribosome.

There is Transfer RNA floating about the cytoplasm. This is short (only three base pairs long) pieces of RNA that have their own unique amino acid attached to them.

The Transfer RNA links up with the Messenger RNA according to their mutually compatible base pairs. The amino acids that the Transfer RNA is carrying link up with each other and detach from the Transfer RNA this is the beginning of a protein chain.