Abstract

This article presents an update on known and unknown biological codes. While the genetic code has been recognized as a code for decades, most other codes were hidden in the shadow of this hallmark discovery. It was the dawn of the new millennium when the histone language and code were proclaimed in the years 2000 and 2001, respectively, marking the start of an explosion in the number of published codes across all biological disciplines since then. Actually, there are hundreds to thousands of biological codes, but only a fraction—although still a substantial number—have been explicitly described as such. A first assessment of those codes allows for a simple categorization into structural and regulatory codes, at the same time maintaining Marcello Barbieri´s initial differentiation of organic versus neural codes. The article reviews prominent codes and showcases restriction-modification and toxin-antitoxin systems as code systems that have gone unrecognized until today. This article should read as a motivation for all those who want to discover ever more new codes—from literature or in the field.