3 Intracellular signalling components

3.1 Introduction

We are now ready to describe in detail the major intracellular signalling pathways responsible for relaying the signal from the surface receptor to evoke a cellular response. This section will deal with signalling molecules that operate at the cytosolic leaflet of the plasma membrane (trimeric G proteins, monomeric G proteins and lipid-modifying enzymes), second messengers (such as Ca²⁺, cAMP, cGMP), protein kinases and phosphatases, and finally transcription factors.