AiS Challenge Team Interim
Team Number: Team 019
School Name: Bloomfield High School
Area of Science: Biology
Project Title: Aging
Aging is the process of growing old or maturing. There are many aging
theories, but most of them reduce down to two categories: Programmed aging
and Wear and Tear aging. Programmed aging is genetically programmed.
Inside the body, the organisms force elderliness and deterioration. They
are intended by nature to age. Wear and Tear is based on environmental
factors. Aging is not genetically programmed. We are researching on the
Programmed aging, and we will focus on the Telomeric Theory of Aging.
In our research, we have learned that a human stem cell has 23 chromosomes
pairs. Each chromosome has two ends, giving 92 chromosome ends in each
cell. At each end of a chromosome is a cap called a telomere. Telomeres
consist of the six-base repeating sequence TTAGGG (2 Thymines, 2 Adenine
and 3 Guanines). A portion of every telomere is lost whenever a cell is
divided; therefore, the telomere shortens gradually. Leonard Hayflick did
one of the most famous experiments in gerontology. He observed that
embryonic fibroblasts (connective tissue cells) in tissue culture would
divide about 50 times before they quit dividing. This 50-division limit
(the Hayflick Limit) seemed to be a property of the cell nucleus or DNA.
Therefore, if an old nucleus is transplanted to a young cell, the nucleus
still divides no more than 50 times. Similarly if a young nucleus is
transplanted to an old cell, the nucleus still divides only 50 times.
Also in our research we found the length of the remaining telomere is a
good sign of how many divisions a dividing cell has left. Once the
telomere is gone, functional genetic DNA is lost with each cell division
and the cells are soon missing essential proteins. Germ cells, stem cells
and cancer cells contain an enzyme called telomerase that replaces lost
telomeres, thus preventing them from experiencing a Hayflick Limit.
Hydrocortisone, a steroid hormone, C21H30O5, produced by the adrenal
cortex, that regulates carbohydrate metabolism and maintains blood
pressure, also can increase the Hayflick Limit, but at the cost of
increased mutation. At conception each human telomere is about 10,000
base pairs long (i.e. about1, 666 TTAGGG repeats), and the typical
chromosome is about 13 thousand times longer (130 million base-pairs).
Nine months later, at birth, the average telomere is half as long as it
was at conception. Telomeres lose an average of eight TTAGGG subunits per
cell division, so half of the telomere length was lost due to the cell
divisions of embryonic development. If cells continue to divide after
having lost their telomeres (i.e. beyond the Hayflick Limit of about 50
cell divisions), they not only malfunction due to lost genes, but the
chromosomes ends start sticking to other chromosomes, increasing the
number of abnormalities. Typically a cell will invoke apoptosis (cell
suicide) mechanisms, which prevent the cell from dividing or becoming
cancerous. The Hayflick Limit itself may be a means of preventing cancer.
Diseases that resemble the telomere abnormalities include:
Hutchinson-Gilford syndrome (childhood progeria), and Downs syndrome.
Our research states in Hutchinson-Gilford syndrome (childhood progeria), a
child is born with abnormally short telomeres. Childhood progeria occurs
once in every 8 million births. At age five the telomeres are about as
long as those of a very elderly person. In Downs syndrome the telomeres
of the immune system cells shorten at an abnormally high rate. An extra
copy of chromosome twenty-one causes Downs syndrome. Chromosome
twenty-one is the shortest human chromosome (50 million base-pairs).
Victims of this disease are vulnerable to infection, due to the rapid
shortening of the telomeres of their leukocytes (white blood cells).
We will further research the Telomeric Theory of Aging. We are in the
process of making a mathematical model of telomere cells dividing. We
will go deeper into our research and figure out if extending the telomeres
length could rejuvenate the cell. If we can rejuvenate the cell then
maybe aging could be controlled or possibly prevented. We will work hard
to find an answer.
Telomeric Theory of Aging http://home.earthlink.net/~excelife/1.html
San Juan College Genl Reference Ctr Gold Science News End Games: Tips of
Chromosomes May Contain Secrets of Cancer and Aging (telomeres)
Telomere Synthesis and Function
Mechanisms of Aging http://www.benbest.com/lifext.aging.html
The Evolution of Aging http://www.azinet.com/articles/Aging_Evolution.html