We were told that all living organisms are made to die, which is not exactly the truth. Unicellular life forms like bacteria don't have to suffer
that fate. An amoeba or a
bacterium becomes old and then divides, yielding two newborn cells. Nothing has
died. So, they are biologically immortal.
Biological aging is named senescence. Bacteria and many unicellular organisms
and even simple multi-cellular organisms like hydra has negligible senescence
as their cells keep dividing. They get killed by other organisms or harsh
environment like high temperature.
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| Bacteria are biologically immortal |
If those creatures can keep their internal structures intact
and working indefinitely, why can't human cells do so?
Let us understand why humans can’t be immortal and why we
die.
First, as our cells get nutrition, they divide and we grow. Eventually
cells lose their ability to multiply. Biologist Hayflick found that human cells
can be grown in the laboratory for only about 40 to 60 rounds of cell division.
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| Our body cells can't divide after 40-60 round of division |
So, after that they don’t renew and we know, whatever doesn’t
renew decays.
Mouse lives for 3 years and its cell can go through 14 to 28
divisions.
The tortoise can live really long, averaging 100 years and
its cells keep dividing for 90 to 120 rounds. So, how long an organism would
live appears to be related to the number of cell divisions its cells can
sustain.
But why can't a cell keep dividing?
Because, each time a cell divides,
the telomeres of chromosome get shorter. When telomeres get too short, the cell
can no longer divide. If you are wandering what is telomere,
a telomere is the end part of a chromatid, which protect our genetic
data and doesn’t allow chromosome to fuse with its neighbor chromosome.
Telomeres are really important.
Telomere gets shorter and shorter with every round of division
When cell divides, chromosome replicates itself, new
chromosome gets little shorter telomere, then that cell again divides and
length of telomere gets shorter. When telomere becomes too short, cell can’t
replicate that chromosome anymore.
And if cell can’t replicate its chromosomes it can’t
divide anymore.
Why does a cell die?
There are many theories as there are many reasons.
Our cells are chemical plant where lots of chemical reactions
taking place continuously.
All products of those reactions are not exactly good for the
cell. Sometimes unstable compound or ions with unpaired electrons are produced.
Those are called free radicals. Free radicals can also be produced because of
light and heat radiation.
These electron hungry free radicals break apart other
molecules. Then those molecules who lost electrons try to steal electrons from
another molecules, thus a chain reaction may start which destroy the whole
work-flow inside cell chemical plant and plant shuts down, cell dies.
But we often heard of antioxidant which is good for us and
this is the thing which can stop free radicals. Antioxidants give electrons to
free radicals but it doesn’t turn to a harmful substance itself after giving
electrons.
Vitamin C, E etc are excellent anti-oxidant.
But anti-oxidants can’t keep a cell alive for ever, though it can extend the life of cells.
But still you have to die because many cells which are given
specialized functions can’t get renewed by division. Like nerves and most of
muscle.
Just think, our nerves make circuit in brain to retain
memories, information of things we have learned. If they divide then those
circuits or connection would be destroyed.
The maintenance credit goes to lysosomes in cells. Lysosomes
produces enzyme to recycle old parts of cells to renew the cells. But many
indigestible debris (lipofuscin) get accumulated inside lisosome and just like
an old machine it loses its ability. Then cell dies as it can’t get renewed.
As your body is made of cells, even the healthiest person of
the earth has to die.
But many other factors like pollution, increase of light and
heat radiation because of global warming also contribute a lot to produce free
radicals in our cells.
Unhealthy diet can disturb the delicate work-flow in the
chemical plant of our body and thus it reduces your life.
So, a healthy diet in a healthy environment can increase your
life-span but you will die one day.
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