Kinetochore: What It Is, Characteristics And Functions Of This Part Of The Chromosome
DNA is the library of life. In the sequence of nucleotides that make up this well-known double helix are the answers to every biological process, since this nucleic acid contains the genetic instructions used in the development and functioning of all living organisms (we consciously exclude viruses).
In eukaryotic cells, DNA is wrapped in a nuclear membrane, but this does not prevent it from being in contact with the rest of the cellular apparatus. Through the processes of transcription and translation (mediated by RNA, enzymes and ribosomes), all the coding information present in the genome can be translated into protein synthesis and, therefore, enables all metabolic processes at the cellular and tissue level.
In addition to this fascinating mechanism, the bases of evolution itself are found in DNA. Thanks to this double helix-shaped biopolymer, living beings inherit information from our fathers and mothers and, in addition, we mutate as species and suffer variations over the centuries. DNA is grouped in our cells in the form of chromosomes, and today we tell you everything about an essential part of them: the kinetochore
We begin by establishing a series of basic terms, because first of all we must know the genetic characteristics of human beings. Both you and I (and with exceptions), have in each and every one of our cells 23 pairs of chromosomes (2n, diploidy), that is, a total of 46. The cells that form tissues are called somatic, and all of them divide by mitosis : Due to this mechanism, every cell derived from another will have the same amount of genetic information, that is, 46 chromosomes or 23 pairs.
On the other hand, our sex cells divide by meiosis, a process by which haploid gametes (n) are formed, which are eggs and sperm, with 23 chromosomes. Thus, when a zygote is created by the fusion of these sexual cells, the condition of diploidy is recovered (23+23:46) and the fetus gives rise to a functional human being after its development. Based on this premise, you will understand that half of your genetic information comes from your father, while the other half comes from your mother’s genome.
Beyond inheritance patterns, it is important to know that DNA is grouped in the nucleus of our cells in a substance called chromatin, which in turn forms a chromosome. If you imagine an X-shaped chromosome and cut it in half on the vertical axis, each of the 2 units obtained are known as chromatids. Based on this premise, We observe the following sections in a normal chromosome :
A chromosome contains hundreds of thousands of genes, so clearly it must undergo a series of changes when a cell is replicated by mitosis, that is, two cell bodies are formed where there was one before. Here the centromere plays an essential role, which could not act without the action of the kinetochore
What is a kinetochore?
The kinetochore is a trilaminar disc-shaped structure, located at the centromere of each chromosome The microtubules of the mitotic spindle are anchored to this unique structure during cell division processes, which we will briefly explain in later lines.
The kinetochore measures between 350 and 500 nanometers in diameter and, thanks to its functionality, the different movements of the chromosomes that are so striking during mitosis are orchestrated In animal chromosomes, there are 2 essential parts: the internal and the external.
The inner kinetochore is organized on highly repeated DNA sequences and assembled on a specialized form of chromatin. The internal part is osmophilic and is in direct contact with the chromosome, about 40 nanometers thick.
On the other hand, the outer kinetochore is a protein structure with many dynamic components that only functions during cell division.
To understand what the purpose of the kinetochore is based on, we must briefly review the process of cell division We are going to focus on mitosis, since it is much easier to explain and serves us perfectly to exemplify the work of this structure. We tell you its summarized phases:
Through this process, where there was once one cell, there are now 2. As you can imagine, Kinetochore functionality shines in metaphase and anaphase
Microtubules are attached to this structure, which are unstable formations of alpha and beta tubulin that give rise to what is known as the mitotic spindle. In metaphase, all the chromosomes are aligned in the center of the cell and, during anaphase, each of the chromatids is dragged thanks to the action of microtubules. Kinetochores are the attachment points where these tubulin formations are anchored, so without them, cell division would be impossible.
Furthermore, it should be noted that The number of microtubules that attach to each kinetochore is highly variable depending on the species consulted For example, in the yeast Saccharomyces cerevisiae a single microtubule is associated with each kinetochore, while in mammals this number easily increases from 15 to 35. In any case, not all the microtubules of the mitotic spindle end up reaching the kinetochores.
Kinetochores and the mitosis checkpoint
The mitosis checkpoint is a fascinating mechanism that ensures correct chromosome division during the process. The mechanisms involved here verify that we can move on to the next phase of the cell cycle during division, since a poorly distributed number of chromosomes in the daughter copies can cause cell death (in the best of cases) or a series of dysfunctions and alterations such as Down syndrome and certain types of cancer.
The kinetochores act as a kind of mitotic checkpoint, since, if they detect any failure, the exit to the next phase is delayed until it is resolved. Of course, this is not a conscious mechanism on the part of the cell, but it reflects the level of refinement that our body has acquired so that everything goes well.
Summary
By exploring kinetochores, we have laid the foundations of human inheritance, the structure of chromosomes and the phases of mitotic division, nothing more, nothing less. With all the knowledge acquired here, it is easy to reach an obvious conclusion, but one that has required hundreds of years of research: the human body is a true work of art from an evolutionary point of view.
Every small section of every part of our body has an essential and irreplaceable function Without going any further, without kinetochores the microtubules could not be anchored and, therefore, it would be impossible to perform mitosis. In the human organic system, every structure counts.
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