Several steps are involved in the translation of an mRNA transcript:

1.  Initiation of translation- involves the binding of mRNA to the ribosome and its
     accessory proteins.  The cap structure is synthesized at the 5' end to insure that
     translation begins at the proper AUG start codon.

2.  Elongation- tRNA molecules read successive mRNA codons to properly place
     amino acids along the growing polypeptide chain.

3.  Termination- Poly(A) polymerase adds approximately 200 adenine residues to
     the 3' end of the mRNA transcript.  Ribosomes stop translation
     when they encounter one of the stop codons (UAA, UAG, or UGA) prior to the
     Poly(A) tail.

Mutant tRNAs called suppressor tRNAs can bind to a stop codon and add an amino acid, preventing termination of translation.  These can help overcome mutations in the DNA which result in mRNA transcripts having stop codons placed incorrectly in the mRNA transcript of an essential protein.