Final answer:
BH3 proteins activate the mitochondrial pathway of apoptosis by binding to and inhibiting the anti-apoptotic proteins of the Bcl-2 family, allowing the release of cytochrome C.
Step-by-step explanation:
The BH3 proteins activate the mitochondrial (intrinsic) pathway of apoptosis by binding to and inhibiting the anti-apoptotic proteins of the Bcl-2 family. These anti-apoptotic proteins prevent the release of cytochrome C from the mitochondria, which is a crucial step in initiating apoptosis. When BH3 proteins bind to the anti-apoptotic proteins, they prevent their inhibitory effect and allow cytochrome C to be released, triggering the apoptotic cascade.
The mitochondrial pathway of apoptosis involves the release of cytochrome C from the mitochondrial intermembrane space into the cytosol. BH3 proteins, also known as Bcl-2 homology 3, are crucial in this process as they activate proapoptotic proteins Bak and Bax. These proteins form channels in the outer mitochondrial membrane, allowing cytochrome C to exit into the cytoplasm. Subsequently, cytochrome C in the cytosol binds to adaptor proteins, forming a complex that activates procaspases. These get converted to active caspases, which are proteolytic enzymes that initiate the cascade leading to cell's auto-digestion and eventual apoptosis.