Life and death of cells
How long does the average cell live? --Karen, Phoenix, Arizona.
This question, certainly interesting, covers much ground because there is no "average" cell. Cells
come in all shapes, sizes, and functions with life spans that vary correspondingly.
Some cells, the bacteria (known more officially as the
prokaryotes), are small simple islands unto themselves.
Often a single-celled organism, they do everything on their
own: move, eat, digest, make energy to run on, reproduce,
and die.
Other cells--the plant and animal cells--associate together
to form vast well-ordered communities, tied with intricate
communication lines. Such cells specialize to perform
different functions. Each specialized cell pays close
attention to its neighbors as it gets food from its surroundings and expels waste into it.
 These cells adhere to, tightly cooperate with, and depend on each other for life. Large co-ops of
similar cells form tissues. Tissues cooperate and form organs. Organs carry out the basic
functions of an organism.
This white blood cell (a neutrophil) is engulfing a microbe (Streptococcus
pyogenes), which appears in the image as a color-enhanced gold 'string of beads' in the lower
right of the picture. (Image courtesy of James A. Sullivan of Cells Alive)
Thus the complex of specialized cells cooperates to accomplish basic tasks of every organism:
move, eat, digest, make energy to run on, reproduce, and die.
This tremendous array of cells has an equally vast spread of life spans. One cell may last a day;
another a lifetime.
"The fully differentiated neutrophil dies within a day," says Gail Sullivan, assistant research
professor of medicine at the University of Virginia Health Science Center. Neutrophils are white
blood cells that find, engulf, and destroy foreign microbes.
Red blood cells, on the other hand, last longer--120 days for humans. They cannot, however,
reproduce themselves. That's the price these cells pay for specialization. They must rely on
another kind of cell (undifferentiated stem cells) to replace dead red blood cells.
And that brings us to an example of a long-living cell: stem cells last a lifetime maintaining a
lifelong supply of both red and white blood cells for an individual.
Even longer lived are bacteria spore, which can live much longer lives than the parent bacteria. If
a bacteria senses bad times (for example, a drought), says Sullivan, it forms spores to suspend
animation and wait out the life-threatening conditions.
Spore found recently in New Mexico may have waited 250 million years for the right conditions
reports John Fleck in the Albuquerque Journal and others in national news. Pennsylvania
biologists William Rosenzweig and Russell Vreeland and New Mexico biologist Dennis Powers
announce an amazing feat. Two thousand feet under the ground at Carlsbad, New Mexico, they
found spore in tiny water bubbles contained in 250-million-year-old rock salt from a vanished
inland sea. They brought the spore back to life and grew bacteria from them!
Rosenzweig tested the genetic material and discovered the bacteria are related to modern Dead
Sea bacteria. The team took such pains in preventing contamination that R. John Parkes of the
University of Bristol in Britain praised their effort in Nature.
Such findings make us wonder about the life spans of cells. Are dormant bacteria essentially
immortal?
Further Surfing:
Cells Alive, a site alive with throbbing cells doing all manner of things from attacking bacteria on
a splinter to committing suicide.
Stem Cells, a Primer by the National Institutes of Health, May 2000
What Is Life? by Brig Klyce
Apoptosis: for every cell, there is a time to live and a time to die
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