Piece #2: The BCL-2 family controls BAK/BAX activation and MOMP. Pro-apoptotic BCL-2 family protein activation is triggered by extra- and intra-cellular signaling. De-repressor BH3-only proteins (green) prevent or disrupt inhibition by anti-apoptotic proteins (red). Direct activator BH3-only proteins (yellow) bind BAK and BAX (blue) to induce their homo-oligomerization and MOMP. Details are provided in the text.