Ribosomes are made of a small part and a large part which surround the mRNA (messenger RNA). In translation, mRNA has the base sequence to make a specific polypeptide. This sequence is originally specified by the DNA, and copied by the mRNA. The polypeptide can be a whole protein. Or, it can be just a part, waiting to be combined with other polypeptides so it can make a whole protein. The polypeptide also has to be folded before it works as a protein.