# Component

A component is a building block of a molecule. Within BioNetGen components are represented graphically as nodes and have two descriptors, name and state, which denote the relevant physical properties.

Occasionally it is useful to specify the connectivity of a node. This is done by choosing which node symbol from the tool bar when creating components and molecules on the Editor Window. The open circle is used for a node that is unconnected to any other node, while the filled circle is used for a node that is connected to a node. The half-filled circle serves as a wildcard and indicates that the node may be either connected or unconnected.

Components as nodes may be joined to other components in other molecules by adding edges between them using the add edge mode option.

Examples of nodes include, a site of post-translational modification in a protein, or phosphorylation of a kinase activation loop.