Final answer:
Cytochrome c, a peripheral membrane protein in the mitochondria, is released during apoptosis and interacts with adapter proteins in the cytosol to initiate a cascade leading to cell self-destruction. Its role in cellular respiration has remained relatively constant over evolutionary time, making it important for inferring evolutionary relationships.
Step-by-step explanation:
The release of cytochrome c from the mitochondria is a significant event in the process of apoptosis, or programmed cell death. Cytochrome c is a peripheral membrane protein found in the mitochondrial intermembrane space, and it is crucial for the electron transport chain. It is involved in transferring electrons between Complex III and Complex IV on the inner mitochondrial membrane surface facing the intermembrane space. However, when a cell is undergoing apoptosis, cytochrome c is released into the cytosol due to the permeabilization of the mitochondrial outer membrane.
In the cytosol, cytochrome c binds to adaptor proteins, forming a complex that can trigger the activation of procaspases to become caspases, which are essential for the cell's self-destruction. The affinity of the cytochrome c-adaptor complex for procaspase allows this interaction to be efficient, facilitating the auto-digestion of the cell. Importantly, the presence of cytochrome c in the cytosol is one of the key steps initiating the cascade of reactions leading to apoptosis.
Interestingly, cytochrome c also plays an important role in understanding evolutionary biology. Due to its critical function in cellular respiration, cytochrome c has remained relatively unchanged throughout millions of years, which allows scientists to use the homology in its amino acid sequences to infer evolutionary relationships among species.