This process continues
until the ribosome encounter a "stop" codon. A stop codon is a series
of three mRNA bases coding for no amino acid and thus terminates the protein
chain. UAA, UAG, UGA are the three stop codons in the genetic code. Stop codons
do not code for an amino acid because a tRNA cannot recognize them. Proteins
called release factors free the protein from the tRNA and the two ribosomal
subunits come apart to be recycled. During this elongation process, the protein
has assumed its three-dimensional functional shape.