Apoptosis Programmed Cell Death Unit 1 Cells and

Apoptosis – Programmed Cell Death Unit 1 – Cells and Proteins Advanced Higher Biology Miss Aitken

Why do we need apoptosis? • There must be a way to carefully control cells which are no longer functioning properly • Programmed cell death occurs in a number of different areas in the body. • Cancer cells are cells which have a mutation in their regulation of apoptosis – this means they become immortal.

How is apoptosis triggered? • Apoptosis is triggered by cell-death signals. • Signals can come from inside the cell or outside the cell. • This is carefully controlled by a set of enzymes called caspases.

Extrinsic Pathway of Apoptosis • Signals which originate from outside of the cell. • Can be triggered by an NK cell that has detected abnormal behaviour • These ligands bind to a surface-receptor, causing a conformational change inside of the cell. This acts as a signal transduction and activates a protein cascade that produces caspases.

Intrinsic Pathway of Apoptosis • Signals which originate from inside of the cell. • Can be triggered by DNA damage or the presence of an abnormal protein like p 53 • This activates a caspase cascade. • Cells may also initiate apoptosis if certain factors required for growth are not present.

Caspase Cascade • Proteins present in the cytoplasm are involved in the caspase cascade. • They start off inactive, and through posttranslational modification, become active. • This allows a rapid response even if the cell’s nucleus is not functioning properly. • Cleavage of the proteins occurs – subunits are removed and reassembled to form active caspases. • An ‘initiator’ caspase starts apoptosis, and activates ‘executioner’ caspases which degrade DNA, keratin and actin. Each executioner can degrade over 600 components.

Fragmentation of the Cell • After cell components have been destroyed, the cell can no longer function and so it breaks into many small parts. • The small parts are engulfed by white blood cells.