| |
| What does research on other animals and organisms
tell us about the human aging process? |
 |
|
|
| |
|
|
 |
What have we learned from animal models of
aging about telomeres? |
|
| |
Our genes are made of DNA and exist in long chains called chromosomes.
Before a cell can divide, it must first double or replicate its DNA, so
that each daughter cell will have a full complement of DNA. Chromosomes
have structures on their ends that are called telomeres, which act as
mooring spots at which the proteins and RNA that actually copy DNA attach.
With each reproduction, bits of those telomeres are lost, until eventually,
after a specific number of divisions (30 to 50 for most human cells),
those telomeres are too short to permit further duplication. Cells possessing
the enzyme telomerase are able to lengthen their telomeres, permitting
unending cell division and granting effective immortality. Over 90% of
human cancers have been found to possess telomerase.
Telomere shortening is believed to play a role in aging. When our cells
have lost the critical length of their telomeres and can no longer reproduce,
they move into a senescent phase. Telomeres have been studied extensively
in animals and much of what has been learned is applicable to human biology.
For additional information about telomeres, see the Telomeres
Information Center.
 Yeast
Roundworms
Fruit
flies
Mice
Nonhuman
primates
|
|
 |
Yeast |
|
| |
Cdc13p is a protein that plays an integral role in allowing the molecules
that control chromosome duplication to bind to telomeres. The process
of chromosome reproduction is quite complex; understanding what happens
in yeast permits greater understanding of what happens in humans.
|
|
|
Roundworms |
|
| |
Scientists have mapped the nucleic acids that make up
telomeres in roundworms. Understanding the structure of the telomere permits
a greater understanding of its function.
|
|
|
Fruit flies |
|
| |
Like some other insects, fruit flies have been found to have the maintain
the integrity of their telomeres without telomerase. They have evolved
different genetic strategies to permit their DNA to be reproduced without
irreversible telomere loss. These findings demonstrate the differences
rather than the similarities between us and other species.
|
|
|
Mice |
|
| |
The length of our telomeres affects the ability of our cells to reproduce.
Some researchers have wondered if telomere length determines life span.
Wild mice (rather than those bred for laboratory study) often have significantly
shorter telomeres than some of the lab strains. However, the researchers
found that there was no correlation between the length of the telomeres
and the length of life. They concluded that though telomeres might determine
the length of the life of cells in culture, they do not determine the
length of life of an animal as a whole.
|
|
|
Nonhuman Primates |
|
| |
Though we share 98% of our genes with our nonhuman primate cousins, interestingly,
recent findings document that monkey species possess longer telomeres
than we do. The level of activity of the enzyme telomerase is similar
when we compare monkeys to ourselves, but we appear to be unique in the
length of our telomeres.
|
|
|
|
|
| |
|
|
 |
     |
 |
previous
chapter
