Anatomy-Lexicon

Telomeres

definition

Telomeres are part of every DNA. They are at the ends of chromosomes and in no case do they code for genes. Unlike the rest of the chromosome, telomeres do not have double-stranded DNA. They are available as a single strand.

In contrast to the rest of the DNA, they also do not have a high variability in the order of the bases, but consist of repeating base sequences. This is important for the fulfillment of their function.

Due to the repetitive sequences, the telomeres of the chromosome curl up in such a way that they do not allow an enzyme to attack the chromosome end. With each cell cycle there is a shortening of the telomeres caused by cell proliferation.

Anatomical intricacies of the telomeres

Each chromosome consists of two strands of DNA that run in different directions, the so-called antiparallel direction. A telomere is located at the end of each side of a DNA strand. Thus, depending on the cell cycle, there are either two or four telomeres per chromosome. In total, there are either 96 or 192 telomeres per cell with 46 chromosomes.

If the DNA strands simply ended blindly, this would give various proteins the opportunity to attack the DNA. In contrast to a large part of the DNA, the telomeres do not carry any information that is important for the function of the cells.

Rather, there is a base sequence in the telomeres that is repeated over and over again. This sequence consists of six bases and has guanine three times, adenosine once and thymine twice. This repetitive sequence ultimately leads to the bases of a telomere base pairing with each other. This leads to a folding of the ends and the telomeres are no longer present as a single strand, but as a coil. For cells to multiply during replication, however, it is necessary for the folded telomeres to unfold.

What are the functions of the telomeres?

Telomeres essentially have two roles. On the one hand, they are important during the normal cell cycle or during the G0 phase. Enzymes exist inside the cells that continuously break down the DNA. This serves on the one hand to ward off intruders, but on the other hand it is also undesirable. This poses an enormous problem for the normal DNA of the cell nucleus and can lead to undesirable events.

To prevent this from happening, there is an overhang, the telomere, on one side at the end of every single DNA strand. Since the telomoer consists of base sequences that do not code for proteins, this alone is a protection for the coding DNA, since it is first broken down. Furthermore, by folding the telomeres, the DNA-degrading enzymes find it difficult to find a point at which they can start their degradation by curling the free DNA end. In addition, folded telomeres provide binding sites for special proteins. These proteins are relatively large in order to protectively surround the DNA end.

On the other hand, the telomeres are important during replication, i.e. during the doubling of DNA. Due to their structure, the responsible enzymes cannot start doubling the DNA at the end of a DNA strand. As a result, there is a loss of base pairs with each cycle and the chromosomes are continuously shortened. So that this does not lead to a premature loss of essential DNA segments, the telomeres are located at the ends. They do not carry any genetically important information and can survive a loss of a few bases without any problems.

This topic could also be of interest to you: Tasks of the cell nucleus

Telomeres Diseases

Telomeres can have serious effects. In the case of such a subsequent effect, damage to the DNA coding for proteins is usually the cause.

Telomeres disease is most often caused by a deficiency in protein complexes (Shelterine), which are located around the telomeres, or caused by the enzyme telomerase. This promotes a disruption of the structure through reduced protection.

Due to the relatively high number of chromosomes, a category of diseases cannot reliably be assigned to a telomeric disease. This means that many different organs can be affected.

Telomeropathy

The term telomeropathy is used for diseases that occur due to damaged telomeres. Telomere disease is usually used as an equivalent term. Because of the irreversible cause of these diseases, all telomeropathies will be chronic.

In telomeropathy, the telomeres are usually shortened to such an extent that the subsequent DNA is attacked due to a lack of the enzyme telomerase or the proteins that form the shelterine complex. Sometimes DNA that codes for proteins is affected, so the damage can be felt in the body.

Telomeropathies include a large number of diseases that are not very specific to telomeropathies. This means that the symptoms are very diverse and often have other causes. The severity of the disease is also very different and the chronic course with the symptoms can be strong or weak.

The more common telomeropathies include pneumonia, cirrhosis of the liver or anemia and damage to the bone marrow.

What role do telomeres play in aging?

As we age, the human body's need for new cells continues. Among other things, this is necessary to maintain the processes in the individual cells of the various organs.

These new cells are created by cell division (Mitosis) as part of the cell cycle. Before division, all cell organelles and the entire DNA are doubled. This process is called replication. Specific enzymes exist for this in every cell. However, due to their structure, the responsible enzymes cannot start doubling the DNA at the end of each DNA strand.

As a result, there is a loss of base pairs with each cycle and the chromosomes are continuously shortened.

The telomeres are located at the ends so that this does not lead to an early loss of important DNA segments. They do not carry any genetically important information and can survive a loss of a few bases without any problems. With old age, however, the telomeres fall below a certain length, which is dangerous and potentially associated with damage.

This leads either to an irreversible cell cycle arrest, the senescence, or to a planned death of the cell. Thus the body continuously loses its potential for renewal and it ages.

Our next article could also be of interest to you: Aging process

What role do they play in cancer development?

Telomeres can also play an essential role in the development of cancer. More often, however, the cause of cancer is a mutation within the DNA strand. In the development of cancer, however, the shortening plays a role as in aging.

With shorter telomeres, cancer is more likely to develop. The reason for this is that there is a higher probability that the part of the DNA double strand that codes for proteins and contains genes will be attacked. The risk factor for this are short telomeres that are already present from birth.

In addition, low levels of the enzyme telomerase and the shelterine protein complex are more likely. The telomeres also play an important role in pre-existing cancer.

As the cells degenerate, there is increased cell growth and increased cell division. This leads to a faster shortening of the telomeres, which makes further degeneration more likely. The cell tries to react to this through various mechanisms, but this is rarely successful in cancer cells.

What is a telomerase?

Telomerase is an enzyme that occurs in every human cell, but cannot be detected in all cells. Telomerase is particularly active in the following cells:

Cells of the bone marrow
Stem cells
Germline cells (Precursors of sperm and egg cells)
embryonic cells

It occurs mainly in the cell nucleus, since this is where its site of action is. The main task of the enzyme is to minimize the base loss of the telomeres of the DNA at the end of the chromosomes during replication. This is essential, because otherwise with each cell division a relatively high loss of DNA due to the structure leads to a reduced life span of the cells.

It is one of the few enzymes that has the function of reverse transcriptase for this purpose. This means that it can generate a new DNA strand from an RNA strand, which is actually a copy of the DNA.

The rest of the enzymes in the human body do not have this function. For this, the telomerase consists of a small section of RNA, which serves as a template for the new section of DNA. To do this, the enzyme takes advantage of the fact that a sequence occurs repeatedly on the telomeres. The base sequence of the RNA is complementary to this repeating sequence. The new strand of DNA is added to the end of the telomere.

Can diet affect telomeres?

It has been established by some medical professionals and researchers that diet affects telomeres. Several studies have already been carried out on this, but some of them are controversial.

A healthy diet is said to increase the activity of telomerase so that the shortening of telomeres during cell division occurs at a slower rate. In addition, the telomeres should even be able to lengthen due to the high activity of telomerase.

The diet should be based on plant-based products whenever possible. A high intake of vitamins, which counteract oxidative stress in the cells, is also important for influencing the telomeres through diet. This results in less damage to the DNA double strand. Omega-3 fatty acids, which are abundant in fatty fish, are also said to have a positive effect.

As with practically all prognoses, in addition to diet, exercise and less physical activity also have a positive effect on the length of the telomeres, which is why you should pay attention to this.

You can read more detailed information on this topic under: Anti-aging and nutrition