Microbiology

Apoptosis

For every cell, there is a time to live and a time to die.

There are two ways in which cells die:

• they are killed by injurious agents
• they are induced to commit suicide

Death by suicide

Cells that are induced to commit suicide:

• shrink
• have their mitochondria break down with the release of cytochrome c
• develop bubble-like blebs on their surface
• have the chromatin (DNA and protein) in their nucleus degraded
• break into small, membrane-wrapped, fragments

The phospholipid phosphatidylserine, which is normally hidden within the plasma membrane is exposed on the surface.This is bound by receptors on phagocytic cells like macrophages and dendritic cells which then engulf the cell fragments. The phagocytic cells secrete cytokines that inhibit inflammation.

The pattern of events in death by suicide is so orderly that the process is often called programmed cell death or PCD. The cellular machinery of programmed cell death turns out to be as intrinsic to the cell as, say, mitosis.

Programmed cell death is also called apoptosis.

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