mRNA is produced from the transcription of DNA in the nucleus. Afte splicing has occured to remove non coding introns from the pre-mRNA, the mRNA leaves the nucleus via nuclear pores. Moving to a ribosome, the mRNA is fed through the structure. tRNA molecules are present and form specific codon to anti-codon bonds with the mRNA. tRNA have associated amino acid molecules which if their anti-codon fits the codon of the mRNA, the amino acid will be added to the newly formed polypeptide.