Figure 2. Regulated gene expression and model network representation. External stimuli (ligands binding to receptors on the cell’s surface) may trigger an alteration in gene expression. Via signal transduction, the most important regulators, the transcription factors, are influenced. They regulate the transcription of DNA to mRNA, which subsequently is translated to proteins. Those regulated biological processes can be transformed to a network model (inference), whose main nodes represent genes or their products (typically on the level of regulated transcription).