Cell Apoptosis

Apoptosis is programmed cell death (PCD). Cells in the body basically kill themselves based on preprogrammed sequences in their genetic code. The process of death utilizes chemical events that change the structure of the cell, and ultimately break it down, either to be used by other cells or expelled from the body as waste. This differs from cell necrosis, in which the cell dies and simply begins to decay, usually releasing harmful substances into the body.

Cells go through apoptosis for a variety of reasons. Cell death can occur in cells that no longer perform a function (for example: the tail of a tadpole as it turns into a frog). Apoptosis can also occur in cells that become a threat to the body, such as cells that have been infected by a virus, cells with damaged DNA, cancer cells, and active auto-immune cells which have served their function and are no longer needed.

Often apoptosis is induced by the production in the cell of p53, a protein that senses DNA damage usually caused by oxidants. (Antioxidants can prevent the damage from occurring in the first place.) P53 is expressed by the p53 gene on the DNA itself. Apoptosis can also be induced by a buildup of proteins that have not been properly processed. Another induction method involves death activator molecules sent from other parts of the body that can bind to receptors on the cell to cause apoptosis.

A typical apoptosis process:

  • The cell begins to shrink.
  • The DNA degrades and the mitochondria breaks down.
  • The cell develops bubble-like structures on its surface called "blebs".
  • The cell breaks down into fragments that are wrapped within a membrane.
  • Nucleotides are released that attract phagocytic cells (cells that eat other cells)
  • A substance called phosphatidylserine appears on the surface of the cell fragments, signaling the phagocytes to consume them.1

In the average human body, about one million cells undergo apoptosis every second. (The body contains 75-100 trillion cells.) When too little apoptosis occurs it can trigger cancer. This may happen as the result of a virus that interferes with the process, or the destruction of both of the p53 genes on human DNA. Too much apoptosis may be at least part of the cause of some chronic diseases such as Parkinson's and Alzheimer's2.

  1. Programmed Cell Death
  2. MedTerms: Definition of Apoptosis

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