Protein Synthesis starts when information in nuclear DNA is copied (transcribed) to messenger RNA (mRNA yellow string). mRNA exits the nucleus via nuclear pores and is read by ribosomes (lumpy blue objects). Transfer RNAs (tRNAs orange L-shaped molecules) bring various amino acids to the ribosomes. The type of tRNA that briefly attaches to the ribosome depends on the code being read from the mRNA. The amino acids are joined together in a chain forming a protein (purple).