Final answer:
Cytochrome c, when released from the mitochondria, leads to apoptosis by forming a complex that activates caspases while its role in the electron transport chain is integral for ATP synthesis. A failure in cytochrome c redox reactions or its inhibition, such as with cyanide poisoning, halts cellular energy production.
Step-by-step explanation:
When cytochrome c is released from the mitochondria, it initiates a cascade of events leading to programmed cell death, or apoptosis. Because cytochrome c is a peripheral membrane protein of the cristae, it can detach and move into the cytosol. Once in the cytosol, cytochrome c binds to adaptor proteins, forming a complex that attracts procaspase, an inactive enzyme precursor. The binding triggers an allosteric change in procaspase, activating it into caspase, which is a proteolytic enzyme responsible for initiating the cellular dismantling processes of apoptosis.
Cytochrome c is also a critical component of the electron transport chain (ETC), where it carries electrons between complex III and complex IV. If cytochrome c fails to undergo redox reactions as a part of the ETC, this will result in a halt of the electron flow, impeding the synthesis of ATP and disrupting the production of cellular energy.
In the event of cyanide poisoning, which inhibits cytochrome c oxidase, the final component of the ETC, the pH of the intermembrane space would be expected to increase because the transfer of H+ ions into the space is halted, reducing their concentration. This inhibition would result in a stop of ATP synthesis, which is driven by the gradient of protons across the inner mitochondrial membrane created by the ETC's activity.