PROTEIN-PROTEIN INTERACTION (PPI). “It appears that all available PPI networks display scale free topology; this topology is surprisingly pervasive, having been previously observed in social networks and the Internet. In scale-free networks, most of the nodes have a small number of interaction partners (degree), but a small subset, the hubs, have a very large number of partners.”
http://www.biochemj.org/content/454/3/361?sa=X&ved=0CDkQ9QEwEWoVChMIzdjAo5n2xgIVovRyCh0HSAum