Final answer:
Cytochrome c activates caspase-9 by binding to adaptor proteins in the cytosol, causing an allosteric change in procaspase-9 that results in its activation and initiates the apoptosis cascade.
Step-by-step explanation:
Cytochrome c plays a critical role in activating caspase-9, which is an essential step in the process of apoptosis, or programmed cell death. When the mitochondria release cytochrome c into the cytosol, it binds to adaptor proteins to form a complex. This complex, in turn, has a high affinity for procaspase-9. Upon binding, an allosteric change occurs in procaspase-9, leading to its activation. The now active caspase-9 initiates a cascade of further caspase activation, resulting in the execution phase of apoptosis, where cellular components are broken down.