Final answer:
Apoptosis is a systematically regulated process of programmed cell death that differs from necrosis, which is an uncontrolled and damaging cell death. Apoptosis involves activation of initiator and executioner procaspases that cascade to dismantle the cell, and can be triggered intrinsically or extrinsically.
Step-by-step explanation:
Apoptosis vs. Necrosis
Apoptosis, often referred to as programmed cell death, is a regulated and controlled process that allows cells to die without causing harm to the organism. It is different from necrosis, which is a form of traumatic cell death resulting from acute cellular injury, leading to the breakdown of cell membranes and the release of potentially damaging molecules into the surrounding tissue.
Mechanism of Apoptosis
The initiation of apoptosis involves the activation of initiator procaspases, such as procaspase-9, which get activated in response to various apoptotic signals, such as DNA damage signaled by the P53 protein. These initiator procaspases cleave and activate executioner procaspases, such as procaspase-3, -6, and -7, which in turn cleave other cellular substrates leading to the characteristic morphological and biochemical features of apoptosis including cell shrinkage, chromatin condensation, nuclear fragmentation, and ultimately the formation of apoptotic bodies. The active caspases are part of a cascade of proteolytic enzymes that play central roles in the disassembly of the cell.
Apoptosis can be triggered through either an intrinsic pathway, involving the release of cytochrome c from the mitochondria mediated by Bcl2 proteins such as Bak and Bax, or through an extrinsic pathway, involving death receptors on the cell membrane.