During Transcription, DNA is initially un-coiled by the enzyme DNA helicase to reveal 2x single nucleotide chains. These are read by RNA polymerase from the 3' to 5' end of the DNA. mRNA is produced here, which diffuses out of the nucleus into the cytoplasm of the cell. 'Junk DNA' or introns are then spliced, leaving only DNA coding for the protein (exons). Translation then occurs whereby mRNA is met by tRNA units, each recognising a specific triplet code of bases. This sequencing of tRNA along the mRNA length allows the corresponding amino acids to be joined together, forming the primary structure of the protein. This is then folded into secondary, tertiary and quarternary structures by other proteins.