Overview

The central dogma of molecular biology describes how one form of biological information (an organism's genetic sequence) is processed in terms of DNA replication, RNA transcription, and protein synthesis. However, a related mystery is yet to be worked out in sufficient detail: how is the information encoded in the DNA (i.e., genotypes) related to cellular functions (i.e., phenotypes)? How do different signals tell different cells to synthesize different proteins?

To tackle these questions we adopt a view of the cell as a machine that processes diverse information. The hardware for cellular information processing consists of specialized biochemical reactions and their associated molecules, forming so-called signal transduction networks. As we have discussed in the previous chapter, the majority of biochemical reactions involve proteins acting as enzymatic catalysts. Reactions in signaling systems are no exception. In fact it is a common motif in signaling systems for enzymes to carry information via regulations of their biochemical activities; activities are modulated by covalent modification or allosteric binding by effector molecules.

A central question in cellular biology is now to elucidate (meaning to develop models with reliable predictive power) the mechanisms by which the cells transducer information and perform their functions. Cellular biochemical signaling systems are customarily visualized as “logic circuits”; the components for the circuitry, now popularly called “modules”, consist of molecules and biochemical reactions.