Final answer:
Cytochrome C binding to APAF-1 in the cytosol leads to the formation of the apoptosome, activating caspases that cause apoptosis. This process is part of the cell's internal machinery to remove damaged cells, and it's regulated by ubiquitin-proteasome system degradation and immune cell-induced apoptosis mechanisms.
Step-by-step explanation:
When cytochrome C binds to APAF-1 (apoptotic protease activating factor 1), it initiates a series of events leading to apoptosis, the programmed cell death. Cytochrome C, released from mitochondria due to stress or cell damage, associates with APAF-1 in the cytosol. This interaction triggers the aggregation of APAF-1 into a heptameric structure known as the apoptosome, which facilitates the recruitment and activation of procaspase-9. The active caspase-9 then cleaves and activates downstream effector caspases, such as caspase-3, leading to the systematic dismantling of cellular components and eventually cell death. This pathway is crucial for maintaining cellular homeostasis and removing damaged cells.