is associated with the protein sequences in the PANTHER protein library through manual curation (Figure 1 and 2). The individual protein sequences are instances of the pathway component. In these cases, a pathway component is typically a group of homologous/orthologous proteins across various organisms that are involved in the same biochemical reaction within the pathway. The second class is reaction, which represents biochemical relationships among different pathway components. Since all PANTHER pathways are in compliance with SBGN-PD, a typical reaction is a transition of an input (or reactant) to an output (a product) controlled by a modifier (Figure 2B). The last class is the cell/tissue type and cellular component, which provides the location where the reaction occurs.
