Most people understand that our genes are stored in our DNA but what is less commonly understood is how the cell determines which genes to use at any one time. The DNA in our cells contain tens of thousands of protein-coding genes whose proteins serve a great variety of purposes. They serve as railroad tracks, precision tunnels, enzymes to speed up reactions and environmental sensors to name just a few. And some proteins go back to the DNA and bind to the double helix, as part of a complex regulatory network that determines which genes to use to make new proteins. In other words, the cell determines which genes, to use to make new proteins, by using existing proteins. But from where did those existing proteins come? Read more