How cells die

Two ways that cells die Death by injury Death by suicide

Cell death from injury Toxic chemicals Lack of ATP or oxygen (necrosis) Mechanical damage

a-POP-tosis programmed cell suicide Cell shrinks Blebs develop on membrane Chromatin is broken up Mitochondria break down Membrane changes so that clean-up cells engulf and digest the remains of the cell

Why cells commit suicide Apoptosis leads to proper development. Apoptosis destroys cells that are a threat to organism. Apoptosis destroys cells with DNA damage. This helps prevent mutant cells and cancer.

Development Apoptosis allows our fingers and toes to form normally. Apoptosis is responsible for the loss of a tail on a tadpole.

Cell threats – viral infection Cells infected with viruses self-destruct before infecting other cells.

Cell threats – destruction of some types of immune cells Some immune cells need to be destroyed when their job is finished. Apoptosis decreases the number of immune cells after infection, so they don’t attack normal tissues. Autoimmune diseases such as lupus and arthritis are caused by immune cells attacking normal body cells.

Immune cells also assist in apoptosis

Cell threats – DNA damage Cells with DNA damage can cause cells to become cancerous. Cells with DNA damage can cause birth defects.

How cells know when it’s time to go... Internal chemical signals are released when the cell is damaged. External chemical signals are present on the cell membrane.

How chemical signals work Both types of chemical signals cause specific molecules to bind to the cell membrane and start the process of apoptosis. One major signal for starting apoptosis is released from damaged mitochondria.

Apoptosis and cancer Cancer causing viruses can block signals that cause apoptosis of the cell. Some types of cancer cells release molecules that block the external signals for apoptosis. Some types of cancer cells do not release the internal signals that cause apoptosis to occur.

Apoptosis and AIDS Only one in every 100,000 cells destroyed in AIDS patients are killed by the virus. The other 999,999 cells are killed because their chemical signals cause apoptosis to occur. Current science does not know why this happens.