apoptosis

Apoptosis is the controlled cell death of eukaryotes, as part of the eukaryotic cell cycle

Apoptosis can occur due to:

• DNA damage

• Viral infection

• Overproduction of cells

• Cell aging

• Inappropriate differentiation or migration of cells.

Increased apoptosis:

• Excessive cell death

• Neurological disorders

• Caused by overproduction of apoptosis stimulating proteins or overstimulation of the death receptor.

Decreased apoptosis:

• Excess cell growth

• Tumours 

• Caused by malfunctions of death receptors

There are 2 pathways for apoptosis, Mitochondrial (Intrinsic) and Death recpetor (Extrinsic) pathways.

Mitochondrial (intrinsic) pathway:

1. DNA damage or viral infection cause pro-apoptosis signals to bind to receptors on the mitochondria; ionising radiation can also damage the mitochondria.

2. After this, Cytochrome C is released from the mitochondria. 

3. Cytochrome C activates Apaf-1, which activates procaspase 9, where it turns into caspase 9, which actiavtes procaspase 3, where it turns into caspase 3, which then cuts up the cytoskeleton.

4. The cell then releases signals to attract white blood cells.

Death receptor (extrinsic) pathway:

1. Eternal cells release a death ligand, FasL, this happens when there is cell overproduction, innapropriate differentiation, or cell age.

2. The FasL binds to FasR on the plasma membrane, which then activates procaspase 8 and turns it into caspase 8, which actiavtes procaspase 3 into capsase 3, which then cuts the cytoskeleton.

Execution: 

1. Cells collapses and forms little bubbles, called blebs, this process is called blebbing.

2. The organelles and nucleus fragment.

3. The blebs then separate from the cell, after which they are called apoptotic bodies. 

4. Macrophages come and engulf these apoptotic bodies through phagocytosis, after which the lysosomes in the macrophage break down the organelles.