Scientists try to capture the complexity of the genetic expression of a protein (left) in artificial in vitro settings (right). (Left) Enzymes (red) in the nucleus transcribe the genetic code onto RNA, stopping at the repressor protein (pink). Messenger RNA (mRNA) carries this information outside the nucleus, where it is translated by ribosomes (enzymes) into proteins (blue). Enzymes also break down proteins (and RNA, not shown) into smaller amino acids. (Right) Karzbrun et al. designed a simple genetic network, made up from the machinery of bacteria, as a starting point to model the same process: “R” enzymes participate in transcription and translation; “X” enzymes break down the mRNA and proteins.