Figure 4. Besides the physical and reactive processes typically associated with chemical systems, a variety of additional biological processes influence how cells respond to extracellular cues.

A sampling of biological processes that orchestrate the cellular responses to an extracellular cue (ligand) are shown as a function of their associated kinetic time scales. With the fastest time scales, ion changes in the cytosol and post-translational modifications influence protein structure. Changes in protein structure alter the affinity of protein interactions. Protein abundance can be altered due to signaling-induced changes in abundance via de novo synthesis, degradation, or dilution within an expanding cell population. Epigenetic changes influence the relationship between transcription factor activation and the resulting protein synthesis by altering promoter binding sites, mRNA stability, or translation. Finally, cellular response can be modified by additional secreted or metabolic cues present within the local microenvironment that can, in turn, be shaped by the cell populations themselves.