The Bcl-2 family are made up of 25 proteins which function in regulating apoptosis, or programmed cell death. Most members such as Bcl-2, Bcl-W, and Bcl-Xl, prevent formations of mitochondrial membrane pores thereby inhibiting caspase activation and apoptosis. Inversely, proteins Bax and Bak promote the permeability of the mitochondria to release cytochrome c to trigger cell death. Other pro-apoptotic members including Bid, Bim, Bad, Bik and Puma, are not as structurally related to Bcl-2. However, they act by binding to and inactivating the antiapoptotic Bcl-2 proteins. Inhibitors to members of the Bcl-2 family can serve as beneficial tools in examining biological processes such as apoptosis and cell proliferation.