True about apoptosis:

Ans.: B (Activation of caspase 3 execution phase)] "The fundamental event In apoptosis is the activation of enzymes called Caspases which are cystein proteases involved in apoptosis by initiating apoptotk signals(via intrinsic or extrinsic pathway) & executing apoptoticprogram(via execution phase)" Apoptosis Intrinsic pathway/ Phase (Mitochondrial pathway) Cytochrome C,Apaf- l, AIF, Caspase9 Extrinsic pathway/ Phase (Death receptor initiated pathway) TNF-Receptor-1, Fas(CD 95), Caspase 8 Execution phase Caspases 3,6,7 THE EXTRINSIC (DEATH RECEPTOR-INITIATED) PATHWAY This pathway is initiated by engagement of cell surface death receptors on a variety of cells.Deatb receptors are members of the tumor necrosis factor receptor family that contain a cytoplasmic domain involved in protein-protein interactions that is called the death domain because it is essential for delivering apoptotic signals. (Some TNF receptor family members do not contain cytoplasmic death domains; their role in triggering apoptosis is much less established). The best-known death receptors are the type 1 TNF receptor (TNFR1) and a related protein called Fas (CD95), but several others have been described. The mechanism of apoptosis induced by these death receptors is well illustrated by Fas The most well characterized ligands of these receptors to dateane FasL, TNF-atpha, Apo3L, and ApoZL. Corresponding receptors are FasR, TN FR1, DR3, and DR4/ D R5, respectively When Fas is cross-1 inked by its ligand, membrane-bound Fas ligand (FasL), three or more molecules of Fas come together, and their cytoplasmic death domains form a binding site for an adapter protein that also contains a death domain and is called FADD (Fas-associated death domain). FADD that is attached to the death receptors in turn binds an inactive form of caspase-8 (and, in humans, caspase-10), again via a death domain. THE INTRINSIC PATHWAY FOR PROGRAMMED CELL DEATH The intrinsic signaling pathway for programmed cell death involves non-receptor-mediated intracellular signals, inducing activities in the mitochondria that initiate apoptosis. Pro-apoptotic proteins activate caspases that mediate the destruction of the cell through many pathways. These proteins also translocate into the cellular nucleus, inducing DNA fragmentation, a hallmark of apoptosis. The regulation of pro-apoptotic events in the mitochondria occurs through activity of members of the Bcl-2 family of proteins and the tumor suppressor protein p53. Members of the Bcl-2 family of proteins may be pro- oranti-apoptotic. The anti-apoptotic proteins are Bcl-2, Bcl-x, Bcl-xL, Bcl-XS, Bcl-w, and BAG. Some of these proteins are currently under investigation as potential targets for anti cancer therapy. Fig: The extrinsic (death receptor-initiated) pathway of apoptosis, illustrated by the events following Fas engagement