Hierarchy panel

Many areas of cellular biology are too large to be represented as a single pathway. Reactome uses a hierarchical organisation that represents broad biological concepts at the uppermost hierarchical level, referred to as ‘top-level’ pathways, which are divided at the next hierarchical level into sub-pathways and frequently further divided into sub-sub pathways. Navigating towards the lower levels of the hierarchy, the topic becomes more focused, eventually to a specific pathway and the individual molecular events, the reactions (and reaction-like events), that are the steps in that pathway. Icons on the left of each entity in the hierarchy indicate its property such as disease or updated. The pathway hierarchy of ‘Signaling by EGFR’ is illustrated in Figure 18.