EVERYTHING YOU NEED TO KNOW ABOUT TELOMERES
What’s a Telomere?
Telomeres are structures found at the tips of our chromosomes. They are made up of a double stranded DNA sequence in which the top strand is 5’-TTAGGG-3’ repeated thousands of times in tandem. Elsewhere in this document telomeres were referred to as something similar to ride tickets at an amusement park in which each ticket comprises about 7 repeats of 5’-TTAGGG-3’. When a person is first conceived as a single cell embryo the telomeres are about 15,000 bases in length. Bases are components of DNA, like beads on a string, and there are four types of bases called A, C, G, and T. Each entire Chromosome is made up of these bases and the very long string of beads can be thought of as being analogous to a very long shoelace in which the caps or aglets of the shoelaces are equivalent to the telomeres. Along the shoelace is found genes that are also made up of these bases. It is, in fact, the sequence of these bases, within our genes, that determines whether our eyes will blue or brown, our hair will be brunette or blonde, our height will be tall or short, etc.
Every time our cells divide our telomeres get a little bit shorter, and this is where all the trouble begins. There is so much cell division needed to go from a single cell embryo to a newborn baby that by the time a person is born their telomeres have already shortened down to 10,000 bases. But that is still OK. That’s like cutting 1/3 of the aglet off of a shoelace. The shoelace still works fine. But the problem doesn’t end there. A person still has a lot more cell divisions to experience as they grown in size, heal their wounds, fight their infections, etc. When telomeres get down to 5,000 bases in length the cells lose the ability to function, and the person dies of old age.
In many cases some tissues will experience increased rates of cell division during a person’s life, resulting in accelerated telomere shortening and early tissue failure. This is often how such ailments as Liver Cirrhosis, Muscular Dystrophy, Multiple Sclerosis, Kidney Fibrosis, Immune Senescence, etc. result. The increased rates of cell division can be caused by a need to repair genetic damage to tissues, such as Muscular Dystrophy, or a need to repair lifestyle damage (such as from drinking alcohol) to tissues, such as Liver Cirrhosis. The resulting accelerated telomere shortening will kill the tissue and often the person sooner than was meant to be.
The reason that telomeres shorten when cells divide is actually due to inefficient replication of the chromosomal DNA by enzymes called DNA polymerases. When cells divide the DNA of the chromosomes needs to be replicated (i.e., duplicated) so that the two new daughter cells each get a copy of the same DNA that the parent cell had. But almost all human cells lack the ability to replicate the DNA completely to the very ends and so the new replicated chromosome becomes shorter than the original chromosome that it was copied from.
What is Telomerase?
But some cells don’t experience this telomere shortening during DNA replication. These cells include most single cell organisms such as yeast, protozoa, and algae. The reason that these cells don’t experience telomere shortening is because they produce the enzyme telomerase that replicates the regions of the ends of the DNA that the polymerases were originally unable to replicate. This results in a complete, non-shortened, copies of the original chromosomes.
Primordial Germ Cells (aka Reproductive Cells) in mammals also don’t experience telomere shortening. Primordial Germ Cells are the cells that produce the sperm and eggs in mammals. If Primordial Germ Cells didn’t produce telomerase, then offspring would be born with shorter telomeres than their parents. And every new generation afterwards would be born with shorter and shorter telomeres until the chromosomes shortened to nothing. Under such circumstances all mammals would have become extinct on earth millions of years ago. So that is why mammals and other animals with linear chromosomes have the enzyme telomerase; they cannot exist as a species without it.