The following section
will teach you the basics of telomeres and telomerase. It will also
introduce you to the potential applications of current telomerase research.
Words in italics are defined in the glossary. At the end of some paragraphs,
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telomeres and telomerase?
better understand telomeres and telomerase, let's first review some
basic principles of biology and genetics. The human body is an organism
formed by adding many organ
systems together. Those organ systems are made of individual
organs. Each organ contains tissues designed for specific functions
like absorption and secretion. Tissues
are made of cells
that have joined together to perform those special functions. Each cell
is then made of smaller components called organelles,
one of which is called the nucleus. The nucleus contains structures
that are actually "packages" of all the genetic information that is
passed from parents to their children. The genetic information, or "genes",
are really just a series of bases called Adenine (A), Guanine (G), Cytosine
(C), and Thymine (T). These base pairs make up our cellular alphabet
and create the sequences, or instructions needed to form our bodies.
In order to grow and age, our bodies must duplicate their cells. This
process is called mitosis.
Mitosis is a process that allows one "parent" cell to divide into two
new "daughter" cells. During mitosis, cells make copies of their genetic
material. Half of the genetic material goes to each new daughter cell.
To make sure that information is successfully passed from one generation
to the next, each chromosome has a special protective cap called a telomere
located at the end of its "arms". Telomeres are controlled by the presence
of the enzyme
telomerase. Now that we have covered some basics, let's explore telomeres,
telomerase, and their importance to you! (view
telomere is a repeating DNA sequence (for example, TTAGGG) at the end
of the body's chromosomes. The telomere can reach a length of 15,000
base pairs. Telomeres function by preventing chromosomes from losing
base pair sequences at their ends. They also stop chromosomes from fusing
to each other. However, each time a cell divides, some of the telomere
is lost (usually 25-200 base pairs per division). When the telomere
becomes too short, the chromosome reaches a "critical length" and can
no longer replicate. This means that a cell becomes "old" and dies by
a process called apoptosis.
Telomere activity is controlled by two mechanisms: erosion and addition.
Erosion, as mentioned, occurs each time a cell divides. Addition is
determined by the activity of telomerase.
also called telomere terminal transferase, is an enzyme made of protein
and RNA subunits
that elongates chromosomes by adding TTAGGG sequences to the end of
existing chromosomes. Telomerase is found in fetal tissues, adult germ
cells, and also tumor cells. Telomerase activity is regulated
during development and has a very low, almost undetectable activity
in somatic (body) cells. Because these somatic cells do not regularly
use telomerase, they age. The result of aging cells is an aging body.
If telomerase is activated in a cell, the cell will continue to grow
and divide. This "immortal cell" theory is important in two areas of
research: aging and cancer.
aging, or senescence,
is the process by which a cell becomes old and dies. It is due to the
shortening of chromosomal telomeres to the point that the chromosome
reaches a critical length. Cellular aging is analogous to a wind up
clock. If the clock stays wound, a cell becomes immortal and constantly
produces new cells. If the clock winds down, the cell stops producing
new cells and dies. Our cells are constantly aging. Being able to make
the body's cells live forever certainly creates some exciting possibilities.
Telomerase research could therefore yield important discoveries related
to the aging process.
cells are a type of malignant
cell. The malignant cells multiply until they form a tumor that grows
uncontrollably. Telomerase has been detected in human cancer cells and
is found to be 10-20 times more active than in normal body cells. This
provides a selective growth advantage to many types of tumors. If telomerase
activity was to be turned off, then telomeres in cancer cells
would shorten, just like they do in normal body cells. This would prevent
the cancer cells from dividing uncontrollably in their early stages
of development. In the event that a tumor has already thoroughly developed,
it may be removed and anti-telomerase therapy could be administered
to prevent relapse. In essence, preventing telomerase from performing
its function would change cancer cells from "immortal" to "mortal".(view
what we have just learned about telomeres and telomerase, it can be
said that scientists are on the verge of discovering many of telomerase's
secrets. In the future, their research in the area of telomerase could
uncover valuable information to combat aging, fight cancer, and even
improve the quality of medical treatment in other areas such as skin
grafts for burn victims, bone marrow transplants, and heart disease.
Who knows how far this could go?