Step 1: Understanding the apoptosome.
The apoptosome is a large protein complex involved in the initiation of apoptosis, which is a programmed cell death process. The apoptosome is formed in response to stress or damage signals, and it plays a crucial role in activating caspases that execute the cell death process.
Step 2: Analyzing the options.
- (A) Cytochrome c is released from mitochondria during apoptosis and is a key molecule that triggers the formation of the apoptosome, but it is not itself a component of the apoptosome.
- (B) Correct: Procaspase 9 is a key component of the apoptosome. When cytochrome c binds to apoptotic protease activating factor-1 (Apaf-1), it activates procaspase 9, which then initiates the caspase cascade leading to cell death.
- (C) Caspase 3 is activated downstream of procaspase 9. It is involved in the execution phase of apoptosis but is not a component of the apoptosome.
- (D) Caspase 8 is involved in the extrinsic apoptotic pathway and does not directly participate in the apoptosome formation.
Step 3: Conclusion.
The apoptosome contains procaspase 9 as a major component.
Final Answer:
\[
\boxed{\text{Procaspase 9 is a component of the apoptosome.}}
\]