The main cellular processes. Conceptual representation of the main cellular processes that occur inside the cell. Signaling cascades receive external signals from the environment, either by binding to an extracellular receptor or, as illustrated, by passing through a channel and binding to an internal receptor. This signal is then propagated through a signaling cascade that involves the sequential phosphorylation of several proteins, leading to gene activations. Gene regulatory networks control the transcription level of genes. Genes are transcribed into RNA molecules, which are subsequently translated into proteins. These proteins are involved in all cellular functions. Some proteins are enzymes involved in the catalysis of metabolic reactions. Metabolic networks obtain energy and carbon from external sources using internal conversion steps. The internal metabolites can be used for cellular growth, or converted into by-products that are excreted by the cell. Their concentration level can also influence gene regulation.