Transcription and translation are the two central processes by which DNA is converted into proteins. Transcription occurs in the nucleus and involves RNA polymerase making an mRNA copy of a gene from DNA. The mRNA is then processed and exported to the cytoplasm. Translation occurs on ribosomes in the cytoplasm, where tRNAs match codons on mRNA to add amino acids in the proper order to form a protein chain. The protein then folds into its final three-dimensional structure to perform its functions in the cell.