Where are the chromosomes? Grade 6, then skipped? But do not worry, we will find the answer to this question, and also determine how important they are for living organisms. What is the mechanism of their placement and construction?
Small digression
Chromosomes are an important part of the gene mechanism. They act as a repository of DNA. Some viruses have single-stranded molecules, but in most cases they are double-stranded and are linear or ring-locked. But DNA is located on chromosomes exclusively in cellular organisms. That is, this repository in viruses is not used in the usual sense, since the microorganism itself plays such a role. When coiled, the molecules are arranged more compactly. Chromosomes are made up of chromatin. This is a special fiber that forms when eukaryotic DNA wraps special protein particles called histones. They are located at a certain interval, so the structure is stable.
About chromosomes
They are the main structural elements of the cell nucleus. Due to the ability of self-reproduction, chromosomes can provide a genetic link between generations. It should be noted the difference in their length between different animals and people: their size can vary from fractions to tens of microns. Nucleoproteins, which are formed from proteins such as protamines and histones, are used as the chemical basis for the construction. Chromosomes are continuously located in the
cell nucleus. And this applies to all possible higher life forms. So, the above statement about where the chromosomes are located in the animal cell can be attributed with the same confidence to plants. Look out the window. What trees can you see behind it? Linden, oak, birch, walnut? Or maybe currant bushes and raspberries? Answering the question about where the chromosomes of plants are located, which were listed, we can say that they are in the same place as in animal organisms - in the
nuclei of cells.
Location of chromosomes in a cell: how to make a choice
Multicellular eukaryotes possess a
diploid set of chromosomes. It is composed of the genome of father and mother. Thanks to the meiosis process, they conjugate with each other. This ensures the flow of the exchange of sites - crossing over. Possible in these cases is the pairing of
homologous chromosomes. This is necessary to ensure the functioning of genes in cells that are not dividing, but are in a resting state. The consequence of this is that the chromosomes are located in the nucleus and that they must not leave its limits to continue the division functions. Of course, finding nucleotide residues in the cell itself is not difficult. But in most cases it is either the genome in the mitochondria, or individual parts of the whole that have split off and are now in "free swimming". Meeting a full chromosome outside the nucleus is very difficult. And if this happens, it is solely due to physical damage.
Chromosome set
This is the name of the entire set of chromosomes that are in the cell nucleus. Each biological species has its own permanent and characteristic set, which was fixed during evolution. It can be of two types: single (or haploid, found in the
reproductive cells of animals) and double (or diploid). Sets differ in the number of chromosomes that are present in them. So, in horses, their number is two. But in the simplest and some spore plants, their number can reach thousands. By the way, if we talk about where the chromosomes of bacteria are located, it should be noted that they, too, are usually located in the nucleus, but it is possible that they will “freely” swim in the cytoplasm. But this applies exclusively to unicellular. And they differ not only in quantity, but also in size. A person has 46 chromosomes in the set.
Chromosome morphology
It is directly related to their spiralization. So, when they are in the phase of interphase, then they are most deployed. But at the beginning of the process of division, chromosomes begin to be intensively shortened by carrying out their spiralization. The greatest degree of this condition falls at the metaphase stage. Relatively short and dense structures form on it. A metaphase chromosome is formed from two chromatids. They, in turn, consist of the so-called elementary threads (chromonemes).
Individual chromosomes
They are distinguished depending on the location of the centromere (primary constriction). If this component is lost, then the chromosomes lose their ability to divide. And so the primary constriction divides the chromosome into two shoulders. Secondary can also form (in this case, the result is called a satellite). Each type of organism has its own specific (numerically, size or shape) sets of chromosomes. If it is double, then it is designated as a karyotype.
Chromosomal theory of heredity
These carriers were first described by I.D. Chistyakov in 1874. In 1901, Wilson drew attention to the presence of parallelism in their behavior. Then he focused on the Mendeleev factors of heredity in meiosis and during fertilization and came to the conclusion that the genes are located on the chromosomes. During the years 1915-1920, Morgan and his employees proved this position. They localized several hundred genes in the Drosophila chromosomes, creating the first genetic map. The data obtained at this time formed the basis for the entire subsequent development of science in this direction. Also, based on this information, a chromosome theory of heredity was developed, according to which the continuity of cells and entire organisms is ensured thanks to these carriers.
Chemical composition
Research continued, and during biochemical and cytochemical experiments in the 30-50s of the last century, it was established from which they were composed. Their composition is as follows:
- Basic proteins (protamines and histones).
- DNA
- Non-histone proteins.
- Variable components. RNA and acidic protein can act in their quality.
Chromosomes are formed from deoxyribonucleoprotein filaments. They can be bundled. In 1953, the structure of the DNA molecule was discovered and the mechanism of its auto-reproduction was disassembled. The knowledge gained about the nucleic code served as the basis for the emergence of a new science - genetics. Now we not only know where the chromosomes are in the cell, but also have an idea of what they are made of. When in ordinary household conversations they talk about the hereditary apparatus, they usually mean one DNA, but now you know that it is only its component.
Sex chromosomes
The genes that are responsible for the gender of the mammal (including humans) are in a special pair. There may be other cases of organization in which everything is determined by the ratio of each type of sex chromosome. Animals with this type of definition are called autosomes. In humans (and other mammals, too), the female gender is determined by the same chromosomes, which are designated as X. For the male, X and U are used. But what about the choice of what gender the child will be? Initially, the female carrier (egg) matures, in which X is located. And sex is always determined by the content of spermatocytes. They in equal proportion (plus / minus) contain both the X and Y chromosomes. From the carrier who is the first to perform fertilization, the sex of the unborn child also depends. And as a result, either a woman (XX) or a man (XU) can arise. So, we not only found out where the chromosomes are in humans, but also figured out the features of their placement and combination when creating a new organism. It is worth noting that this process is somewhat facilitated in simpler life forms, therefore, getting acquainted with what they have and how it proceeds, you can notice small differences from the model described here.
Functioning
Chromosomal DNA can be represented as a matrix that works to synthesize specific molecules of messenger RNA. But this process can proceed only under the condition of despiralization of a certain site. Speaking about the possibility of the gene or the whole chromosome working, it should be noted that certain conditions may be necessary for their functioning. You probably heard about insulin? The gene responsible for its production is in the whole human body. But he can activate and work only when he is in the necessary cells that create the pancreas. And there are quite a few such cases. If we talk about the exclusion of the whole chromosome from metabolism, then here we can recall the formation of the body of sex chromatin.
Human chromosomes
In 1922, Peytner hypothesized that a person has 48 chromosomes. Of course, this was not said from scratch, but based on certain data. But in 1956, scientists Tire and Levan, using the latest methods for studying the human genome, found that in fact a person has only 46 chromosomes. They also gave a description of our karyotype. Numbering pairs goes from one to twenty-three. Although the last pair is often not assigned a number, they are separately named what it consists of.
Conclusion
So, we have determined throughout the article what role chromosomes have, where they are located and how they are built. Of course, the main attention was given to the human genome, but animals and plants were also considered. We know where the chromosomes are located in the cell, the features of their location, as well as the possible transformations that can occur with them. If we talk about the genome, then remember that it can be in other parts, and not just the nucleus. But what exactly will be the daughter objects is affected precisely by what is available in the chromosomes. Moreover, the characteristics of the organism do not greatly depend on the number of these. So, talking about where the chromosomes are located in the plant cell and animal organisms, we believe that our task was completed.