Question

1) FAS ligand (on the killer lymphocyte) binds to FAS protein (on target cell). Adaptor proteins and procaspase-8 aggregate.

2) Procaspase 8 activated to caspase 8
3) Caspase 8 initiates caspase cascade --> apoptosis.
DNA is packaged into nucleosomes, nucleases preferentially cut DNA between nucleosomes. DNA wrap around the histones at 200 bp intervals.

Answer 1

The FAS ligand on cytotoxic T cells and NK cells binds to the FAS molecule on target cells, leading to apoptosis through a caspase cascade. The nucleosome structure of DNA facilitates this programmed cell death, while additional mechanisms ensure damaged cells are also targeted for apoptosis.

Step-by-step explanation:

The FAS ligand is a molecule that is expressed on the surface of cytotoxic T cells and NK cells. When it binds to the FAS molecule on a target cell, it triggers a series of events leading to apoptosis, which is a form of programmed cell death. The process begins with the aggregation of adapter proteins and procaspase-8, which is then activated to caspase 8. This active enzyme initiates a caspase cascade that results in the systematic breakdown and death of the cell. DNA within the cell is packaged into nucleosomes, with digestion occurring preferentially between these nucleosomes.

Cytotoxic T cells can also become activated upon recognizing antigens presented by MHC I molecules on infected cells, subsequently releasing perforin and granzymes that also induce apoptosis.

In the event of DNA damage that can't be repaired, mechanisms including the signaling of p53 and subsequent proteasome activity target the damaged cells for apoptosis to maintain cellular integrity and prevent the proliferation of dysfunctional cells.