Apoptosis Pathway

 

Apoptosis Pathway

Function: Apoptosis, or programmed cell death, is a critical process for removing damaged or unnecessary cells, ensuring tissue homeostasis.

Location: Apoptosis occurs in various tissues throughout the body.

Steps and Enzymes Involved:

1. Intrinsic (Mitochondrial) Pathway:

   • Step 1: Internal stress signals (e.g., DNA damage) lead to the activation of pro-apoptotic proteins such as Bax and Bak.

   • Step 2: Bax and Bak oligomerize and form pores in the mitochondrial membrane, causing the release of cytochrome c.

   • Step 3: Cytochrome c binds to Apaf-1, forming the apoptosome, which recruits and activates caspase-9.

   • Step 4: Caspase-9 cleaves and activates executioner caspases, such as caspase-3 and caspase-7.

   • Step 5: Executioner caspases degrade cellular components, leading to cell death.

2. Extrinsic (Death Receptor) Pathway:

   • Step 1: Extracellular signals (e.g., Fas ligand) bind to death receptors (e.g., Fas, TNF receptor).

   • Step 2: Receptor binding recruits adaptor proteins (e.g., FADD) and procaspase-8, forming the death-inducing signaling complex (DISC).

   • Step 3: Procaspase-8 is cleaved to active caspase-8.

   • Step 4: Caspase-8 activates executioner caspases, such as caspase-3, leading to cell death.

   • Step 5: In some cases, caspase-8 can also activate the intrinsic pathway by cleaving Bid into tBid, which activates Bax and Bak.