Question

Which events describe when a cell undergoes apoptosis?

The plasma membrane moves phosphatidylserine to its inner leaflet.

The nucleus breaks down before the plasma membrane becomes permeable.

The plasma membrane becomes permeable, leading to mitochondrial damage.

The cell lyses, losing 30% of its volume.

Answer 1

These are the events of apoptosis:

The nucleus breaks down before the plasma membrane becomes permeable.

The plasma membrane becomes permeable, leading to mitochondrial damage.

The cell lyses, losing 30% of its volume.

Biochemical changes:

1. Proteolysis of cytoskeletal proteins.

2. Protein-protein cross linkages.

3. After initial pyknosis of nucleus, there is the fragmentation of chromatin by activation of nuclease.

4. Appearance of phosphatidylserine on the outer surface of cell membrane.

5. In some forms of apoptosis, appearance of an adhesive glycoprotein thrombospondin on the outer surface of apoptotic bodies.

6. Appearance of phosphatidylserine and thrombospondin on the outer surface of apoptotic cell facilitates early recognition by macrophages for phagocytosis prior to appearance of inflammatory cells.

Molecular mechanisms:

Activation of intrinsic pathway, which causes increased cell membrane permeability, chromation fragmentation, mitochondrial apoptotic factor release and cell fragmentation and shrinkage. After that extrinsic pathway activated, which initiates caspase pathway and ultimately phagocytosis of dead cells.