Telomeres: what are they, characteristics and how are they linked to age

Time passes for everyone, and that is an undeniable reality. Conceiving life without death is impossible, since all organic matter degrades, loses shape and is transformed. Without going any further, the most appropriate definition that occurs to us to define life from a biological point of view is the following: the intermediate state between birth and death.

Time passes in an inalienable way, yes, but you will be surprised to know that it does not do the same for everyone. Chronological (chronometric) age indicates the movement of the clock's hands, but this physical magnitude has nothing to do with what happens inside our bodies. The phases of a biological process do not have the same quality or nature as those of a physical process insofar as they are merely successive.

In the physiological study of living beings, the phases of a process are determined by the dynamics "of the intrinsic process", and not by the impositions of a physical element, such as a clock. Thus, a 40-year-old alcoholic may have the liver of an 80-year-old, for example, while a An octogenarian athlete may have the typical lower body musculature of a sedentary 60-year-old years.

Time passes, yes, but biological age may be different from what the calendar indicates.

Many of the parameters that modify the biological age of living tissues are completely linked to the individual's lifestyle, But there are other complex and fascinating concepts that explain, in part, why the cellular aging process is unique and interchangeable. We explain the secret of life and death with a term as exciting as it is useful: know everything about telomeres.

• Related article: "What are the differences between chronological age and biological age?"

How are the chromosomes organized and where are the telomeres?

Let's start from the beginning, like life itself. Human beings present, in each of our cells, the DNA enclosed in a nucleus. Through a series of processes that are not our concern here, the information from the DNA is transported from the nucleus to the ribosomes of the cell cytoplasm, so that they can synthesize proteins. Protein synthesis is the basis of the metabolism of living beings, so it could be said that DNA contains all the information necessary for life to be such.

In humans, DNA condenses into chromatin, forming chromosomes. Each non-sexual cell in our body (in general) has 23 pairs of chromosomes (46 total), of which which 23 come from the female gamete (n) and 23 from the male (n), which when joined together form a zygote (2n). The parts of a chromosome are as follows:

• Film and matrix: each chromosome is delimited by a membrane that encloses a gelatinous substance.
• Chromonemes: filamentous structure that makes up each of the sister chromatids (each half of the chromosome being an "X" shaped chromatid)
• Chromomers: succession of granules that accompany the cromonema in its length.
• Centromere: place where the two sister chromatids meet. For us to understand each other, it is the center of the "X".
• Telomeres: the terminal parts of the chromosome, its "tips."

We have left a specific section in the inkwell in order not to get lost in technicalities, but we have already come across the term that concerns us here for the first time. Time to explore it thoroughly.

What are telomeres?

Based on what we've seen so far, the telomere defines itself almost on its own: is the tip of the chromosome. Telomeres are non-coding regions of DNA (they do not have information necessary for protein synthesis) highly repetitive, whose function is to provide stability to chromosomes in eukaryotic cells throughout their lifetime. Based on the existence of these structures, we can partially explain two phenomena that take the breath away of every human being: aging and cancer. Let's see how.

1. During DNA duplication, telomeres do not replicate in their entirety

Somatic cells divide by mitosis and, for this to be possible, the DNA of the original cell has to be duplicated, which will give rise to the line of descendants. With each replication process, and due to certain characteristics of the enzymes that make it possible, telomeres get shorter.

Telomere length in humans decreases at a rate of 24.8-27.7 base pairs per year. With time and cell division, the telomeres of the descendant cells' chromosomes become so short that the cell can no longer divide and, therefore, with the death of the last cellular entities, the death of the tissue. Making a parallel of “walking around the house”, it is as if we remove a little water every time we pass it from one glass to another. At first it may not be noticeable, but after repeating the process X times, the transfer can no longer be done, as there is no water left to transfer.

For this reason, telomeres are said to be an excellent marker of biological age: Based on its length, scientists can estimate how far a cell group is ahead, and therefore the entire organism. Telomere shortening is part of the normal aging process, but certain agents associated with a style specific life spans can promote chromosomal DNA damage and hence faster shortening of telomeres.

• You may be interested in: "Chromosomes: what are they, characteristics and how they work"

2. The importance of telomerase

We have explained the mechanism of aging, but things get even more interesting if we know that, as incredible as It seems, the body itself has the solution for immortality on a theoretical level, at least in the early stages of life. lifetime.

Telomerase is an enzyme in charge of maintaining telomere length by adding repeated genetic sequences. This biological process has a “trick”: the activity is present in the cells of the germ line and certain hematopoietic cells, but mature somatic cells inhibit their functionality after birth. Thus, it is the organism itself that encodes its programmed degradation.

3. Telomeres and cancer

Current studies suggest that humans could reverse the process of cellular senescence if artificially increase telomerase activity in somatic cells that form the tissues of our body. Unfortunately, this could have a double effect: in experimental settings, if telomerase activity is stimulated and certain tumor suppression genes are inactivated, it occurs a cellular immortalization that significantly promotes the appearance of a tumor.

We go further in this line of thought, since 75-80% of cancers arising from somatic cells present telomerase activity. This does not necessarily mean that telomerase causes cancer, but everything seems to indicate that high levels of this enzyme are a clear indication of the possible malignancy of a tumor. If a cell is immortal, it can replicate indefinitely: we are explaining almost word for word the formation of a cancer.

Based on this premise, various anti-telomerase treatments are being developed in the experimental setting. In cell cultures, the results are promising to say the least: in some cancer cell lines, by inhibiting telomerase activity, spontaneous death of the line occurs after about 25 divisionssince telomeres are shortened and cannot be replaced in any way.

Resume

After exposing data like this, it is impossible not to feel hopeful. Cancer is one of the most important and tragic health problems today, because after each death and each figure there is a story of struggle, sadness and hope. A neoplastic tumor is not just a group of cells that grow uncontrollably: it is fear, a battle of science versus physiology, acceptance or denial and, in the worst case, the early loss of a lifetime.

Cellular senescence mechanisms help us understand tissue aging and the process that leads to death, but the ultimate goal is not to find immortality. The real challenge today is to save all those lives that are hanging by a thread by a group of rebel cells that mutated to turn against their host.

Bibliographic references:

• Arvelo, F., & Morales, A. (2004). Telomere, telomerase and cancer. Venezuelan Scientific Act, 55, 288-303.
• Couto, A. B. (2008). Telomerase: fountain of youth for the cell. Medisur: Electronic Journal of Medical Sciences in Cienfuegos, 6 (2), 68-71.
• The influence on lifestyle of telomeres and longevity, genotype. Picked up on March 4 in https://genotipia.com/estilo-vida-telomeros-longevidad/
• Membrive Moyano, J. (2017). Telomerase enzyme as a therapeutic target.
• Moyzis, R. K. (1991). The human telomere. Research and Science, (181), 24-32.
• Salamanca-Gómez, F. (1997). Telomerase. Immortalize without maligning. Gac Med Mex, 8, 385.
• Telomere, NIH. Picked up on March 4 in https://www.genome.gov/es/genetics-glossary/Telomero
• Vargas, E., & Espinoza, R. (2013). Time and biological age. Arbor, 189 (760), 022.