home Boiler room On the importance of studying mitochondrial DNA. Mitochondrial DNA mutations Human mitochondrial DNA contains genes encoding

On the importance of studying mitochondrial DNA. Mitochondrial DNA mutations Human mitochondrial DNA contains genes encoding

Human genome [Encyclopedia written in four letters] Tarantula Vyacheslav Zalmanovich

CHROMOSOME 25 - IMPORTANT ADDENDUM (mitochondrial genome)

Small spool but precious.

Russian proverb

When people now loudly announce the complete sequencing of the human genome, they usually mean the nuclear genome. Against this background, it is somehow forgotten that cells contain DNA molecules located not only in chromosomes, but also in the already mentioned specific intracellular structures such as mitochondria. And this is also the human genome, but it is called mitochondrial, and DNA is called mitochondrial (abbreviated mitDNA). MitDNA is now sometimes called chromosome 25 or the M chromosome. This DNA was sequenced back in 1981 by the already mentioned F. Sanger, which was also a sensation at one time, which, however, had a resonance incomparably less than the sequencing of the nuclear genome. What is this 25th human chromosome?

In a human cell there are from 100 to 1000 mitochondria, each of which contains from 2 to 10 molecules of circular mitDNA with a length of 16569 bp. Thus, the size of the mitochondrial genome is approximately 200,000 times smaller than the nuclear genome. Interestingly, the size of mitDNA in humans is one of the smallest among higher organisms (eukaryotes). For example, in yeast, mitDNA consists of 78,520 bp. Human mitDNA contains 37 genes encoding 13 protein chains, 22 tRNAs and 2 ribosomal RNAs (rRNAs) (Fig. 30). Protein chains are part of proteins that are primarily involved in a critical intracellular process called oxidative phosphorylation, which provides the cell with energy. Due to oxidative phosphorylation in mitochondria, more than 90% of special ATP molecules, which are the basis of cell energy, are produced.

Rice. thirty. Structure of the human mitochondrial genome (mitDNA). mitDNA contains 22 genes encoding tRNAs, 2 ribosomal genes ( 16S And 12S rRNA) and 13 protein-coding genes. Arrows indicate the direction of gene transcription. Abbreviations: ND1-ND6, ND4L- genes of subunits of the NAD-H-dehydrogenase complex; COI–COIII- genes for cytochrome c oxidase subunits; ATP6, ATP8- genes for ATP synthetase subunits; Cyt b- cytochrome b gene

In total, 87 genes are involved in the process of oxidative phosphorylation, but all the missing 74 are encoded not by the mitochondrial, but by the nuclear genome. Interestingly, regions similar to mitDNA are found in the nuclear genome. It is assumed that in the process of evolution and in various pathologies, migration of part of mitDNA into the nuclear genome took place.

It is important that the structure of the mitochondrial genome differs significantly from the nuclear one. First of all, mitDNA is characterized by a very compact arrangement of genes, as in the bacterial genome. Unlike the nuclear genome, mitochondrial genes are adjacent to each other and there are practically no intergenic spaces between them. In some cases, they even overlap by one nucleotide: the last nucleotide of one gene is the first in the next one. That is, genes are packed into mitochondrial DNA, like herring in a barrel. In addition, most mitochondrial genes do not contain structures such as introns that are characteristic of nuclear genes. But that's not all the differences. It turned out, in particular, that mitDNA is not subject to modifications such as methylation, which is characteristic of nuclear DNA.

However, the researchers were especially surprised by the genetic code used in mitDNA. Although the genetic code is universal (with very few exceptions) throughout the living world, mitochondria use an unusual version of it. Most codons in mitochondrial genes are similar to those found in nuclear DNA, but along with this there are also fundamental differences. Four codons in human mitDNA have changed their meaning. The termination codons were AGA and AGG. The UGA codon, which is a termination codon in nuclear DNA, not only does not stop translation in mitDNA, but encodes the amino acid tryptophan. The amino acid methionine is encoded not by one codon AUG, but also by the codon AUA, which in the nuclear genome encodes the amino acid isoleucine.

MitDNA is responsible for the synthesis of just a few mitochondrial proteins in the cell. But these proteins are very important for the cell, since they participate in one of the most important processes - providing the cell with energy. Thus, mitDNA is a very valuable addition to the Encyclopedia of Man. Proteins encoded directly by mitDNA genes are synthesized immediately in mitochondria. For this purpose, it uses its own RNA polymerase and its own protein synthesis apparatus. The reason is clear - the genetic code of mitochondria is special, and a special biosynthesis system is needed.

Not all proteins that are needed for the autonomous existence of mitochondria are encoded by the mitochondrial genome and synthesized here. Their genome is too small for this. Most of the mitochondrial proteins and individual subunits of these proteins are encoded by the main, i.e., nuclear genome and synthesized in the cytoplasm of cells. They are then transported to mitochondria, where they interact with specific proteins encoded by mitDNA. Thus, there is a close relationship between the nuclear and mitochondrial genomes; they complement each other.

Why did it happen in the evolution of the cell that a very small part of the DNA is not contained in the chromosomes of the nucleus, but separately inside the mitochondria? What is the need or advantage of this distribution of genetic material is not yet known. Many hypotheses have been invented to explain this amazing fact. One of the first was expressed by R. Altman back in 1890. However, it remains relevant today. According to this point of view, mitochondria appeared in the cells of higher organisms not during intracellular development and differentiation, but as a result of the natural symbiosis of higher organisms with lower aerobic organisms. This explanation suggests that the mitochondrial genetic code is more ancient than the code used in nuclear DNA in modern organisms.

But along with this, another point of view was expressed, which so far equally has the right to exist. According to the latter, after the transition of most genes from mitDNA to nuclear DNA, some mutations occurred in the apparatus that ensures protein synthesis in mitochondria. In order for the translation process not to be disrupted, special mutations were required in the mitDNA genes, which would “compensate” for the violations and allow the altered protein synthesis apparatus to carry out its work. Based on this assumption, then the mitochondrial code should not be considered as more ancient, but, on the contrary, rather as younger.

In any case, the mitDNA language is, in a certain sense, “jargon”. Why does mitochondria need it? A parallel can be drawn here with the jargon of certain social or professional groups. They use jargon to hide their intentions and actions from outsiders and to avoid other people's interference in their affairs. It is possible that mitDNA, thanks to the use of a modified code - jargon - is isolated from the protein-synthesizing apparatus of the cell, specializing in performing one, but very important function for the cell - energy production.

It has been noted that the mitochondrial genome is more vulnerable than the nuclear genome. As a result, various types of mutations often occur in it (point mutations, small losses of DNA - deletions and, conversely, insertions - insertions). Numerous human diseases associated with changes in mitDNA have now been identified. Pathological mutations are found in almost all mitochondrial genes. At the same time, a huge variety of clinical signs caused by the same molecular damage is noted. A relationship has been found between some mutations and changes in the expression of miDNA genes and the occurrence of cancer. In particular, increased transcription of the gene encoding one of the chains of the protein complex involved in supplying cells with energy (subunit II of cytochrome c oxidase) has been repeatedly noted in breast cancer and lymphomas. Some, fortunately rare, severe hereditary human diseases are also caused by mutations in individual miDNA genes. In Russia there is now a special program for the diagnosis and prevention of mitochondrial diseases.

Another surprising fact about mitDNA concerns its inheritance. It turned out that mitDNA is transmitted from generation to generation in a fundamentally different way than chromosomal DNA. The human body develops from a fertilized egg, which contains the chromosomes of both parents. During fertilization, a sperm enters the egg with a set of paternal chromosomes, but virtually no paternal mitochondria and, therefore, without any paternal mitDNA. Only the egg provides its mitDNA to the embryo. This leads to an important consequence: mitDNA is transmitted only through the female line. We all receive mitDNA only from our mother, and she even earlier from hers, and so on in the series of only female generations. Sons, unlike daughters, do not pass on their mitDNA - the chain will break. In this way, DNA is formed into clones - hereditary lines that can only branch (if a woman has several daughters), but unlike chromosomal DNA, they cannot unite in one organism and create new genetic combinations. For this reason, it was interesting to compare mitDNA in representatives of different human ethnic populations, that is, races and nationalities. This kind of comparison began back in the late 80s of the last century and continues to this day. We'll talk more about this later.

Thus, basic cellular processes such as transcription, translation, replication, and miDNA repair are highly dependent on the nuclear genome, but it is not yet completely clear how these two genomes are integrated with each other. Studying the mechanisms of intergenomic interaction can be useful in many respects, in particular for understanding the integral picture of various human pathologies, including malignant cell degeneration.

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Mitochondria are found not only in plant cells, but also in animal and fungal cells. These organelles are more versatile than plastids. DNA in mitochondria was first discovered in 1963 (M. Naas) immediately after the discovery of DNA in plastids. Despite the similarity of the functions and structure of mitochondria in all three kingdoms of eukaryotes, their genetic organization is quite different, so the organization of mitochondrial genomes in these kingdoms is usually considered separately, identifying common features of genome organization.

The physicochemical composition of mitochondrial DNA is different in different kingdoms. In plants it is quite constant: from 45 to 47% of DNA consists of GC pairs. In animals and fungi, it varies more significantly: from 21 to 50% of HC pairs.

In multicellular animals, the size of the mitochondrial genome ranges from 14.5 to 19.5 kb. In practice, it is always one circular DNA molecule. For example, human mitochondrial DNA is a circular molecule measuring 16,569 nucleotide pairs. This size can be expressed in other units - in the form of molecular weight - 10 6 daltons or in the form of the length of the molecular contour - 5 microns. The primary structure of this molecule is completely determined. Mitochondria contain their own translation apparatus - i.e. own 70S ribosomes, similar to chloroplast or prokaryotic ones and consisting of two subunits, own messenger RNA, necessary enzymes and protein factors. Their genome encodes 12S and 16S ribosomal RNAs, as well as 22 transfer RNAs. In addition, mitochondrial DNA encodes 13 polypeptides, of which 12 have been identified. All coding sequences are located directly next to each other. In extreme cases, they are separated by only a few nucleotides. Non-coding sequences, i.e. no introns. Following the coding sequence there is almost always a transfer RNA gene. For example, the order is as follows: phenylalanine transfer RNA - 12S ribosomal RNA gene - valine transfer RNA - 16S ribosomal RNA gene - leucine transfer RNA, etc. This order is characteristic not only of human mitochondria, it is very conservative and characteristic of all animals: fruit flies, bulls, mice, birds, reptiles and other animals.

Most of the genes are located in the heavy chain; in the light chain there are only genes for eight transport RNAs and one structural gene. Thus, unlike all other genomes, in the mitochondrial genome both chains are meaningful.

Although the order of genes in animal mitochondria is the same, it has been found that the genes themselves have different conservation. The most variable is the nucleotide sequence of the origin of replication and a number of structural genes. The most conserved sequences are located in ribosomal RNA genes and some structural genes, including the ATPase coding sequence.

It should be noted that the universality of the genetic code is disrupted in the mitochondrial genome. For example, human mitochondria use the AUA triplet as a codon for methionine, not isoleucine, like everyone else, and the UGA triplet, used in the standard genetic dictionary as a stop codon, codes for tryptophan in mitochondria.

In general, human mitochondrial DNA looks the same as that of other mammals: mice and bulls. Despite the fact that these are far from closely related species, the sizes of their mitochondrial DNA are quite close to each other: 16,569; 16,295; and 16,338 base pairs, respectively. Transfer RNA genes share some sense genes. The most important of the structural genes are the genes for cytochrome oxidase, NADH dehydrogenase, cytochrome C oxidoreductase and ATP synthetase (Fig. 4).

The map of the human mitochondrial genome, in addition to genes, also shows five well-known human diseases that are inherited through the maternal line and caused by mutations in the mitochondrial genome.

For example, Leber's disease - optic atrophy - is caused by a mutation in the NADH dehydrogenase gene. The same disease can also be caused by a mutation in the cytochrome gene b and other loci. In total, four loci are known to be disrupted and can cause the same mutant phenotype. In addition, the same map shows four more diseases associated with defects in the brain, muscles, heart, kidneys and liver. All these diseases are inherited on the maternal line, and if the mother has not only defective, but also normal mitochondrial DNA and mitochondria, then a sorting of mutant and normal organelles occurs, and the offspring can have both organelles in different proportions, and we can also observe somatic splitting, when individual parts of the body do not have these defects.

Rice. 4 Structure of the mammalian mitochondrial genome based on the complete sequence of human, mouse and bovine mitochondrial DNA

Thus, the small mitochondrial genome of animals can encode extremely important functions of the body and largely determine its normal development.

Just like the plastid genome, the mitochondrial genome encodes only part of the mitochondrial polypeptides (Table 1) and the phenomenon of double coding is observed. For example, some of the subunits of the ATPase complex are encoded by the nucleus, while the other part is encoded by the mitochondrial genome. Most of the genes encoding ribosomal myochondrial RNAs and proteins, as well as transcription and translation enzymes, are encoded by the cell nucleus.

05.05.2015 13.10.2015

All information about the structure of the human body and its predisposition to diseases is encrypted in the form of DNA molecules. The main information is located in the cell nuclei. However, 5% of DNA is localized in mitochondria.

What are mitochondria called?

Mitochondria are cellular organelles of eukaryotes that are needed in order to convert the energy contained in nutrients into compounds that can be absorbed by cells. Therefore, they are often called “energy stations”, because without them the existence of the body is impossible.
These organelles acquired their own genetic information due to the fact that they were previously bacteria. After they entered the cells of the host organism, they were unable to retain their genome, while they transferred part of their own genome to the cell nucleus of the host organism. Therefore, now their DNA (mtDNA) contains only a part, namely 37 genes, of the original amount. Mainly, they encrypt the mechanism of transformation of glucose into compounds - carbon dioxide and water with the production of energy (ATP and NADP), without which the existence of the host organism is impossible.

What is unique about mtDNA?

The main property inherent in mitochondrial DNA is that it can be inherited only through the mother's line. In this case, all children (men or women) can receive mitochondria from the egg. This happens due to the fact that female eggs contain a higher number of these organelles (up to 1000 times) than male sperm. As a result, the daughter organism receives them only from its mother. Therefore, their inheritance from the paternal cell is completely impossible.
It is known that mitochondrial genes were passed on to us from the distant past - from our promother - “mitochondrial Eve”, who is the common ancestor of all people on the planet on the maternal side. Therefore, these molecules are considered the most ideal object for genetic examinations to establish maternal kinship.

How is kinship determined?

Mitochondrial genes have many point mutations, making them highly variable. This allows us to establish kinship. During genetic examination, using special genetic analyzers - sequencers, individual point nucleotide changes in the genotype, their similarity or difference, are determined. In people who are not related on their mother's side, the mitochondrial genomes differ significantly.
Determining kinship is possible thanks to the amazing characteristics of the mitochondrial genotype:
they are not subject to recombination, so molecules change only through the process of mutation, which can occur over a millennium;
possibility of isolation from any biological materials;
if there is a lack of biomaterial or degradation of the nuclear genome, mtDNA can become the only source for analysis due to the huge number of its copies;
Due to the large number of mutations compared to the nuclear genes of cells, high accuracy is achieved when analyzing genetic material.

What can be determined through genetic testing?

Genetic testing of mtDNA will help in diagnosing the following cases.
1. To establish kinship between people on the mother’s side: between a grandfather (or grandmother) and a grandson, a brother and sister, an uncle (or aunt) and a nephew.
2. When analyzing a small amount of biomaterial. After all, each cell contains mtDNA in significant quantities (100 - 10,000), while nuclear DNA contains only 2 copies for each 23 chromosomes.
3. When identifying ancient biomaterial – a shelf life of more than a thousand years. It is thanks to this property that scientists were able to identify genetic material from the remains of members of the Romanov family.
4. In the absence of other material, even one hair contains a significant amount of mtDNA.
5. When determining the belonging of genes to the genealogical branches of humanity (African, American, Middle Eastern, European haplogroup and others), thanks to which it is possible to determine the origin of a person.

Mitochondrial diseases and their diagnosis

Mitochondrial diseases manifest themselves mainly due to defects in the mtDNA of cells associated with a significant susceptibility of these organelles to mutations. Today there are already about 400 diseases associated with their defects.
Normally, each cell can include both normal mitochondria and those with certain disorders. Often, signs of the disease do not manifest themselves at all. However, when the process of energy synthesis weakens, the manifestation of such diseases is observed in them. These diseases are primarily associated with disorders of the muscular or nervous systems. As a rule, with such diseases there is a late onset of clinical manifestations. The incidence of these diseases is 1:200 people. It is known that the presence of mitochondrial mutations can cause nephrotic syndrome during pregnancy and even sudden death of the infant. Therefore, researchers are making active attempts to solve these problems associated with the treatment and transmission of genetic diseases of this type from mothers to children.

How is aging related to mitochondria?

Reorganization of the genome of these organelles was also discovered when analyzing the mechanism of aging of the body. Researchers at Hopkins University published results from monitoring the blood levels of 16,000 elderly American people, demonstrating that the decrease in the amount of mtDNA was directly related to the age of the patients.

Most of the issues considered today have become the basis of a new science - “mitochondrial medicine”, which was formed as a separate direction in the 20th century. Prediction and treatment of diseases associated with mitochondrial genome disorders, genetic diagnostics are its primary tasks.

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Mitochondrial genetics

1. Formal genetics of mitochondria

Unlike plastids, mitochondria are found in all eukaryotes: plants, animals and fungi. Mitochondria of all three kingdoms perform the same function, and their structure is generally similar. Mitochondria are round structures ranging in size from 1 micron (Fig. 1).

Rice. 1 Electron micrograph of leaf mesophyll mitochondria

However, in some cases, mitochondria can be combined into a fairly long tubular curved structure. The internal contents of mitochondria are called the matrix. The matrix contains thin fibrils and granules. It was found that the granules are mitochondrial ribosomes, differing in size and density from the ribosomes of the cytoplasm. Mitochondria, like other organelles, are surrounded by an outer double membrane. The outer membrane of mitochondria is similar to the outer membrane of plastids, the nucleus and the membrane of the endoplasmic reticulum. The inner membrane of mitochondria forms invaginations - cristae. It is on the surface of the inner membrane that all the main enzyme ensembles that provide the functions of mitochondria are located. There are methods for separating the inner and outer membranes of mitochondria. Since the outer membrane of mitochondria is less dense and irreversibly swells in a phosphate solution, this leads to its rupture and separation from the inner one. After treating isolated mitochondria with phosphate, the outer and inner membranes of these organelles can be separated by centrifugation. If you look at them with an electron microscope, they look like transparent hollow spheres, and the volume of the sphere formed by the inner membrane is much higher than the volume of the sphere of the outer membrane. Therefore, the volumetric structure of mitochondria is easy to imagine as a large ball placed inside a small ball. In this case, numerous folds, the so-called cristae, will appear at the inner membrane. The activity of processes occurring in mitochondria is directly related to the number and size of cristae. The larger the surface of the cristae and, consequently, the surface of the inner membrane, the more active these processes are. Consequently, the inner membrane of mitochondria changes in size depending on the functional state of the organelles.

Inner and outer membranes differ in density (the inner one is denser), in permeability (the inner one has highly specific permeability, the outer one has nonspecific permeability), different enzyme compositions and different ratios of proteins to lipids.

The inner membrane of mitochondria is unique in its structure. It contains multicomponent protein-enzyme complexes that carry out electron transfer, oxidative phospholation, fatty acid chain synthesis, as well as proteins that regulate the transport of small molecules into the inner cavity of mitochondria.

Mitochondria, like plastids, never arise “de novo”. Even organisms living in anaerobic conditions have structures similar to mitochondria. If, for example, the same strain of yeast is grown under aerobic and anaerobic conditions, then in cells grown under anaerobic conditions the size of mitochondria changes, but their number does not decrease.

The division of mitochondria, just like plastids, is carried out using amitosis, with the formation of dumbbell-shaped figures and their subsequent ligation.

In some cases, it was possible to demonstrate the synchronicity of mitochondrial division with the cell nucleus and their fairly accurate distribution among daughter cells in some biological objects. Thus, in ciliates, complete synchrony of mitochondrial division along with the cell nucleus is shown. In mitotically dividing plant cells and dividing roundworm spermatocytes, it has been shown that mitochondria are quite precisely distributed along the spindle.

Historically, almost all formal mitochondrial genetics has been studied in fungi and primarily in yeast. In other organisms there are only isolated facts of connection of certain characteristics with mitochondria. The life cycle of yeast is shown in the figure

Rice. 2 Life cycle Saccharomyces cerevisiae

Yeast is a unicellular but multinucleate organism. They spend a significant part of their lives in haplophase and, therefore, their nuclei are haploid. Haploid clones having opposite sex factors (or types of interbreeding), A And A, can merge with each other. Haploid clones with the same types of crossing cannot participate in fertilization. After fertilization, the nuclei fuse and diploid clones are formed. In diploid clones, sporulation and meiosis occur, an ascus is formed, giving rise to haploid clones of two opposite types of crossability A And A in equal proportions. Naturally, simple Mendelian genes will be split in the same way as the gene that controls the sex factor, i.e. will give a 1:1 split.

Yeast in the zygotic phase is heterozygous and can reproduce in two ways: vegetative and generative. During vegetative propagation, they simply divide, and several diploid nuclei enter the resulting cells. In addition, vegetative propagation can also occur through budding. In the formed buds, the nuclei are also diploid. Naturally, during vegetative reproduction no splitting of nuclear genes occurs - heterozygotes remain heterozygotes.

During generative reproduction, meiosis occurs and cells with haploid nuclei, called ascospores, are formed. Ascospores are haploid, and they split into an equal number of ascospores with dominant and recessive alleles, i.e. 1:1.

Thus, if 1:1 segregation is not observed, then this could indicate to us that these genes are possibly non-Mendelian and therefore possibly cytoplasmic.

The existence of an extranuclear mutant in yeast was first demonstrated by the French researcher B. Effrussi back in 1949. These mutants exhibited respiratory defects and poor growth. They did not contain some cytochromes. Such mutants could be obtained in large quantities (sometimes up to 100%) under the influence of acridine dyes. But they can also occur spontaneously with a frequency of up to 1%. These mutants are called " petite", from the French word for "small".

When these mutants were crossed with normal strains, all the offspring were normal without exception. Although for other genetic markers, such as the need for adenine and thiamine, the split into sex-type factors was normal - 1:1.

If you randomly select cells from the first generation of hybrids and cross them again with mutants petite, all the offspring were normal again, although sometimes rare mutant offspring appeared with a frequency of less than 1%. Those. they appeared with almost the same frequency as the spontaneous emergence of these mutants. It was possible to select these hybrids again and cross them with normal ones with the same result. If we assume that these are mutations of nuclear genes, then this could be represented as the result of splitting at 20 independent loci. The emergence of a mutant with simultaneous mutation in 20 loci is an almost incredible event.

R. Wright and D. Lederberg obtained convincing evidence that these mutants are not nuclear. The design of their experiment was as follows. When yeast cells merge, the nuclei do not fuse immediately, and at this moment buds can be deposited that still contain haploid nuclei from both one and the other parent. Such haploid buds spontaneously diploidize (A --> AA; a --> aa). If one strain, for example, with a mutation petite marked by an inability to grow on arginine, and the second - not petite, is marked by an inability to grow on tryptophan, then by selecting buds from such hybrids, we select parental strains based on nuclear genes. What happens to the cytoplasmic ones? As a result of the experiment of R. Wright and D. Lederberg, the following was revealed. Out of 91 clones, 6 clones were found that had the same nucleus as non-clones. petite mutant, but the phenotype is typical petite. Consequently, this phenotype is determined not by the nucleus, but independently of it, and this mutation could be called non-nuclear.

Nuclear mutations were later discovered petite. In total, about 20 such mutants were discovered. All of them mendelized normally and the progeny of ascospores gave normal 2:2 cleavage, although phenotypically they were very similar to cytoplasmic mutants. When crossing cytoplasmic petite with nuclear ones, it was discovered that zygotes acquire the ability to breathe normally, and then splitting occurs 2: Thus, the complementation test proved that we are dealing with mutants of different localization. The discovery of nuclear and cytoplasmic mutants with impaired mitochondrial function also indicated that not all functions of these organelles are encoded by cytoplasmic genes. Some of them encode nuclear genes.

Subsequently, B. Effrussi discovered another similar phenotype as petite, but the inheritance of this mutation occurred in a different way. When crossing mutants petite with normal cells, all offspring acquired the property of growing slowly, and the splitting was 0:4. The first type of cytoplasmic mutants, which produced only normal offspring, was therefore called neutral, and the second, which produced only mutant ones, was called suppressive, or dominant, petite. Suppressiveness in this case is a kind of dominance. But this is a special kind of dominance, when the recessive allele is not just hidden in the heterozygote, it simply disappears completely. Numerous experiments have shown that suppressive mutants petite are also cytoplasmic, since the factors causing their appearance are not inherited along with the nucleus.

Subsequent molecular studies revealed that suppressive mutants petite unlike neutral ones, they have shorter mitochondrial DNA molecules, consisting almost exclusively of AT pairs. Most likely, the suppressive effect is based on the faster proliferation of such mitochondrial DNA and, as a result, the displacement of normal mitochondrial DNA.

Thus, in cytoplasmic mutants of the type petite there are either relatively small deletions in mitochondrial DNA (neutral mutants petite), or total rearrangements of the mitochondrial genome - (suppressive mutants petite).

In addition, mutants with incomplete suppression were discovered, i.e. the ability to produce a certain percentage of individuals of the normal type - 10, 20, 30 and even about 50 percent.

It turned out that the degree of suppression depends on the influences of the external environment - temperature, substrate, etc. Nuclear mutants did not show such a dependence, which made it possible to distinguish incompletely suppressive cytoplasmic petite from nuclear.

After obtaining data on cytoplasmic antibiotic resistance mutants in Chlamydomonas, antibiotic resistance mutations began to be obtained in yeast. A number of such mutants also turned out to be cytoplasmic. When crossing, for example, erythromycin-sensitive with erythromycin-resistant ERsXERr, all offspring were erythromycin sensitive Ers(i.e. the same as the wild type) and no cleavage occurred. The same result was demonstrated with resistance mutants to other antibiotics. However, if buds are selected immediately after the formation of the zygote, then mutant phenotypes can be found among them.

In dihybrid crossing, i.e. when crossing two cytoplasmic mutants sensitive to different antibiotics, for example, resistant to chloramphenicol, but sensitive to erythromycin with sensitive to chloramphenicol, but resistant to erythromycin CrERsXCsERr, the phenotype of only one of the parents predominated in the offspring - CrERs. At the same time, when selecting from the buds immediately after fertilization, not only parental classes of phenotypes were discovered, but also recombinants: CrERrAndCsERs, those. sensitive or resistant to both antibiotics. The presence of recombinants showed for the first time that mitochondrial genes can recombine in the same way as nuclear ones. At the same time, in contrast to experiments on the recombination of plastid genes in Chlamydomonas, recombination polarity was discovered in yeast, i.e. unequal number of recombinant phenotypes depending on the direction of crossing. Recombination polarity has been explained as the presence of a special genetic sex factor in the mitochondrial genome. This factor was designated as u+ and u-. The parent form having the factor u+, i.e. the female parent provides preferential transmission (higher frequency of transmission) of its markers. When crossing same-sex parents for this mitochondrial factor, recombination polarity is not observed and an equal number of recombinants is obtained. The sex factor of mitochondria itself is inherited regardless of the sex of the organism.

In reality, do cytoplasmic organelles—mitochondrions in the generally accepted sense—have sex? We can assume that it exists if we believe that E. coli has it.

But the main thing was that with the help of the many mutations obtained and the detection of recombination of mitochondrial genes, their mapping became possible.

In experiments on crossing mutations like petite with antibiotic resistance mutations, it was found that at least all suppressive mutations petite Antibiotic resistance genes are lost in crosses. This has been shown to occur because suppressive petite have extensive areas of damage to mitochondrial DNA, and in this case it is simply impossible to expect recombination. When mutations of respiratory failure were induced in mutants with resistance to certain antibiotics, it turned out that resistance markers were sometimes lost. When producing mutants with respiratory failure using mutants with double resistance to antibiotics as the initial form, the resulting mutants defective in respiration could lose both resistance markers or only one of them. This suggested that the respiratory failure mutants represented some degree of deletion of mitochondrial DNA, and therefore this could also be used to map the mitochondrial genome.

In Neurospora in 1952, K. Mitchell discovered the first slow-growing mutant, subsequently named MI-1 (abbreviation for English "maternal inheritance" - maternal inheritance). Inheritance of this mutation occurred depending on the direction of crossing, and all offspring were the same in phenotype as the maternal form. This probably occurs because the male gamete in Neurospora does not contribute cytoplasm during fertilization. The connection of this spontaneously occurring mutation with mitochondria was indicated not only by maternal inheritance and differences in reciprocal crosses, but also by the fact that they lacked cytochromes a And b in the electron transfer system.

Subsequently, other slow-growing strains of Neurospora associated with mitochondrial respiratory failure were obtained. Some of them, for example, are mutants MI-3 And MI-4, as it turned out, they were inherited in the same way as the mutant MI-1, while the other part, for example, are mutants S115 And S117 exhibited normal Mendelian monohybrid inheritance. This is reminiscent of other similar cases where the phenotype of organelles, chloroplasts, and mitochondria changes when both nuclear and cytoplasmic mutations occur, indicating that both cytoplasmic and nuclear genetic systems jointly control their functions.

Subsequently, several suppressor genes were discovered, the introduction of which restored the growth rate in slow-growing mutants. It is interesting to note that each of these suppressors restored growth rate in only one of the mutants. For example, a suppressor gene called f, restored the growth rate of the cytoplasmic mutant MI-1, but not in the other cytoplasmic mutant MI-3 or MI-4, and not in nuclear mutants S115 And S117. Other suppressors acted similarly. If, after many generations, suppressor genes are removed from fungi by crossing, the mutant cytoplasmic phenotype will again appear. A similar interaction of nuclear and cytoplasmic genes can be observed in higher plants, for example, during the inheritance of the trait of male sterility in many plants.

When crossing nuclear and cytoplasmic slow-growing mutants with each other, independent inheritance of nuclear and cytoplasmic genes was shown.

For example, when crossing wild type x (MI-1 xS115) offspring F 1 (MI-1 xS115) was phenotypically homogeneous - all individuals were slow growing, and the offspring of return or test crosses were wild type x (MI-1 xS115) no longer contained mutations MI-1 and split along the nuclear gene S-115 in a 1:1 ratio.

Crossing cytoplasmic mutants with each other did not give any new results, since cytoplasmic mutants, at least in Neurospora, demonstrate strictly maternal inheritance during sexual reproduction. Meanwhile, different cytoplasmic mutants, although they had in principle the same phenotype - slow growth - phenotypic differences between them could still be detected, since they had different degrees of slow growth. However, strict maternal inheritance during sexual reproduction did not allow two cytoplasmic mutations to be combined into a cytoget (cytoplasmic heterozygote), which made recombination of cytoplasmic genes and, consequently, their mapping impossible.

A way out of this situation was found through the fusion of neurospora hyphae, which made it possible to combine various nuclear and non-nuclear genomes in one cell.

When creating various cytogets, the following results were obtained:

MI-1 / wild type -- all offspring are only wild type;

MI-3 / wild type - part of the offspring of the wild type, and the other part grows at the speed characteristic of the mutant MI-3;

MI-1 / MI-Z-- most of the offspring with the phenotype MI-3 and a small proportion of offspring with the phenotype MI-1;

MI-1 / MI-4 -- initially a wild-type phenotype, and then split into phenotypes MI-1 And MI-4.

Thus, in the latter case, complementation of cytoplasmic mutations was detected, indicating that these mutations occurred in different regions of the mitochondrial genome.

Subsequently, other cytoplasmic mutations of Neurospora were obtained. The method of fusion of hyphae and the production of cytogets made it possible to hope for the production of various recombinants and the subsequent construction of a genetic map of Neurospora. However, this was hampered by the fact that Neurospora did not produce a large variety of cytoplasmic mutations such as in Chlamydomonas or yeast.

Subsequently, various non-chromosomal mutations obtained from Neurospora were studied using molecular biology methods and were able to be associated with the mitochondrial genome.

In another Podospore mushroom, a mutation was discovered that causes the phenomenon of premature aging. In mutants, the viability of the culture gradually decreased upon reseeding. With reciprocal crosses, the maternal nature of inheritance of the aging phenomenon was clarified. However, maternal inheritance was incomplete. The trait is transmitted both sexually and by joining mycelia. The presence of splitting, although irregular, indicates the corpuscular nature of the inheritance of the trait. Quite a lot of research has been carried out to show that this is not an infectious agent, but a mitochondrial gene. Although complete molecular data are not currently available, it is already clear that these are also mutations of the mitochondrial genome. The presence of the aging gene in the mitochondrial genome has given rise to a lot of speculation on gerontological topics, and some doctors believe that aging in humans is associated not only with changes in the functions of mitochondria, but also with changes in their genome.

Despite the speculative nature of the idea of a connection between gerontological processes in humans and changes in mitochondrial DNA, new data on the study of variability in the human mitochondrial genome confirm this.

Since ancient times, a fairly large number of diseases have been known in humans that are inherited along the maternal line - from the mother to all descendants. These diseases are quite rare, probably due to the fact that they are transmitted only by the female sex. In addition, large deletion changes in mitochondrial DNA, of course, most often lead to either death in the embryonic period or to impaired reproductive functions. In any case, they are effectively swept aside by natural selection.

The formal genetic approach, which was quite well applied to the study of cytoplasmic genes in model objects (Chlamydomonas, yeast, etc.), was not so successful for the analysis of cytoplasmically inherited traits in humans, and therefore the most that could be learned from the analysis of pedigrees was that that such hereditary diseases still exist.

In addition to the well-known syndrome of optic nerve atrophy (Leber's disease or hereditary optic neuropathy), there are other diseases inherited in an extranuclear manner. These diseases are associated, first of all, with impaired functioning of muscles, brain, heart, endocrine systems and are associated with insufficiently active mitochondrial function in certain organs. There is even a mitochondrially-mediated form of diabetes.

Only with the help of molecular methods was it possible to identify the nature of these diseases. A study of various families with Leber disease showed that in different cases there are mutations in different parts of the mitochondrial genome.

Most often, families with hereditary cytoplasmic diseases exhibit heteroplasmy and mothers have both normal and mutant mitochondrial DNA, resulting in offspring with both mutant and normal plasmatypes.

The relationship between human age and mitochondrial DNA has also been shown using molecular biology techniques. Studies of mitochondrial DNA in people of different ages have shown that in older people the percentage of mutant mitochondrial DNA in brain and heart cells rapidly increases. In addition, studies of some hereditary syndromes show that patients with them also have an increased frequency of mitochondrial DNA mutations, which may be the reason for the reduction in life expectancy.

In addition to mutations of the mitochondrial genome, leading to serious pathologies of the body, many fairly neutral mutations of the mitochondrial genome have been discovered among various populations of human races. These extensive studies of thousands of people from all continents are helping to reconstruct the origins and evolution of man. By comparing human mitochondrial DNA with that of apes (gorilla, orangutan, chimpanzee) and assuming that the divergence of humans and apes occurred approximately 13 million years ago, it is possible to calculate the number of years required for a single base pair to change. Subsequently, by comparing the divergence of mitochondrial DNA in different human races, it was possible to determine the place of birth of the first woman, one might say Eve, and the time of human settlement across different continents (Fig. 3).

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Rice. 3 Human settlement, according to D. Wallace, based on the analysis of mitochondrial DNA variability. The numbers indicate the time of settlement of this territory in thousands of years ago.

Since the most variable mitochondrial DNA was found among African aborigines, it can be assumed that the “foremother” of the human race was an African woman. This happened approximately 100,000 years ago. Approximately 70,000 years ago, humans began to populate central Asia through the Middle East and Saudi Arabia, and a little later into Southeast Asia, Indonesia and Australia. About 50,000 years ago, people appeared in Europe. The same data showed that the settlement of the American continent occurred in two stages: first 30,000 years ago through Berengia (the land that existed at that time connecting America and Asia) from the North to the very south of the American continent, and then 8,000 years ago also from Northeast Asia to eastern North America. Settlers on the Pacific Islands appeared relatively recently - several thousand years ago.

It should be noted that these data, based on a comparative analysis of mitochondrial DNA, are in fairly good agreement with both archaeological data and linguistic analysis.

The use of mitochondrial DNA to analyze the history of mankind became possible because the mitochondrial genome is relatively small in size, is inherited exclusively through the maternal line, and, unlike nuclear genes, does not recombine.

Mitochondrial genome

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Rice. 4 Structure of the mammalian mitochondrial genome based on the complete sequence of human, mouse and bovine mitochondrial DNA

Thus, the small mitochondrial genome of animals can encode extremely important functions of the body and largely determine its normal development.

Table 1

Animal mitochondrial DNA genes

mitochondrion genome neurospora mesophyll

animal genome:

1. compact arrangement of genes on mtDNA;

absence of introns in genes;

3. absence of non-coding regions in mtDNA, except for ORI regions;

4. location of tRNA genes between other genes;

5. high similarity in genome size and gene arrangement in different species;

6. the presence of one ORI for each mtDNA strand;

7. symmetrical transcription of both strands;

8. the presence, in principle, of one transcription initiation region for each DNA strand;

9. absence of 5 / - and 3 / - terminal non-coding sequences in mRNA;

10. mRNA maturation as a result of cleavage of the primary transcript into tRNA sequences.

In fungi, the size of the mitochondrial genome is on average much larger and ranges from 17.3 to 101 kb. Moreover, in addition to the main, usually circular DNA molecule, from one to 4 plasmid-like circular or linear molecules ranging in size from 1 to 13 kb are found. The size of the mitochondrial genome in yeast varies not only between different species, but even between different strains. The main reasons for significant differences in the mitochondrial genome in fungi are the presence or absence of introns. In different species of yeast, for example, the size of mitochondrial DNA ranges from 57 to 85 kb.

The presence of introns and mitochondrial DNA molecules of various size classes is the most characteristic feature that distinguishes fungal mitochondria from animal mitochondria. Introns break many sequences - ribosomal RNA genes, genes of some structural proteins encoding mitochondrial enzymes. The presence of most introns is not necessary for the normal functioning of mitochondria. Yeast strains have been artificially constructed that are completely devoid of mitochondrial introns.

Many introns of yeast mitochondrial DNA contain open reading frames that encode muturases involved in splicing, while other introns contain coding sequences for endonucleases and even reverse transcriptases.

All the genes found in the mitochondrial DNA of animals are also present in fungi. In addition, other genes were found in fungi: they have a larger number of tRNA genes, genes for the 6th, 8th and 9th subunits of the ATPase complex were found, a number of new structural genes and a number of genes with unknown function (Table 2 ).

table 2

Yeast mitochondrial DNA genes

Components of mitochondria
Ribosomal RNA	rns(21 S),rnl(15 S)
Ribosomal proteins: small subunit
Transfer RNAs
Cytochrome b(complex III)	Withob (or cyb)
Cytochrome With oxidase (complex IV)	cox 1, cox 2, coxd 3
ATP synthase	atp6, atp8, atp9
Intron-encoded off: RNA maturases Endonucleases Reverse transcriptase-like proteins	aI1, aI2
Unidentified reading frames

In yeast mitochondrial DNA, only 2 ribosomal RNA genes and only 1 ribosomal protein gene were found. This protein is located in the small subunit of the ribosome. The ribosomal protein gene is quite variable in size even among different strains, which is why it received the name variable ( Var l). The remaining proteins and RNA of mitochondrial ribosomes are encoded by nuclear genes. 24 transfer RNA genes ensure the transport of all amino acids to the site of protein synthesis, and only one transfer RNA, transporting lysine, is imported from the cytoplasm and encoded by the nucleus. All transfer RNAs of yeast mitochondria are encoded by the same DNA strand, and only one of them is encoded by the opposite strand. None of the transport DNA genes have introns. Cytochrome b protein genes and cytochrome C protein genes can have many introns - from 5 to 9.

From the above data it follows that the structural proteins encoded by the yeast mitochondrial genome are clearly insufficient for the functioning of these organelles and most of them are encoded by the nuclear genome.

Characteristic features of the organization and expression of mitochondrialfungal genome:

1. significant diversity in the sets and arrangement of mitochondrial genes in different species;

a wide variety of ways to organize genetic material - from the compact organization of the genome to the free distribution of genes along mtDNA with extended non-coding sequences between genes;

3. mosaic structure of a number of genes;

4. significant intraspecific variations in mtDNA size associated with the presence of “optional” introns;

5. the ability of individual mtDNA segments to be excised and amplified with the formation of a defective mitochondrial genome;

6. the presence of one or more ORIs, in each of which replication is initiated bidirectionally;

7. location of all mitochondrial genes on one strand of mtDNA and asymmetric transcription of mtDNA;

8.multiplicity of mtDNA transcription units;

9. a variety of signals for processing primary transcripts, which can be either tRNA or oligonucleotide blocks of another type - depending on the species;

10. In most cases, mRNAs contain extended terminal non-coding sequences.

The most complex organization of the mitochondrial genome is in higher plants. Their mitochondrial genome is a set of supercoiled double-stranded circular and/or linear molecules. All mitochondrial genome sequences can be organized into one large circular "chromosome", and the observed different size classes of mitochondrial DNA are most likely the result of recombination processes. At least on spinach, species of two genera Brassica And Raphanus, sugar beets and wheat, it was shown that the reason for such dispersion of the mitochondrial genome is the recombination of homologous regions of mitochondrial DNA. Due to the presence of directly oriented two or three families of repeats ranging in size from 1 to 14 kb, mitochondrial DNA molecules are capable of active inter- and intragenomic rearrangements. As a result of such rearrangements, mitochondrial DNA can be present in the form of molecules of various size classes.

So, for example, in cruciferous Brassica campestris Mitochondrial DNA is present in the form of three types of circular molecules. The first type contains the complete genome - 218 kb, the second - 135 and the third - 83 kb. Subgenomic rings are formed as a result of recombination of genomic rings having a pair of direct repeats 2 kb in length.

In wheat, the size of the mitochondrial genome is much larger - 430 kb, and there are more than 10 direct recombination repeats, as a result, during electron microscopic observation, many rings of various sizes can be seen, but no one has observed one large circular molecule, perhaps in this state, the wheat mitochondrial genome is never present. In Marchantia moss and other cruciferous Brassica hirta There are no direct recombination repeats and, perhaps, this is why mitochondrial DNA is in the form of circular molecules of the same size class. However, for mitochondrial DNA of higher plants this is the exception rather than the rule. In most higher plants, the mitochondrial genome contains both recombination repeats and mitochondrial DNA molecules of various size classes.

The number of molecules of the same size class can vary greatly in different plant tissues, depending on the state of the plant and environmental conditions. A change in the numerical ratios of mitochondrial DNA molecules of different size classes was noted during plant cultivation in vivo And in vitro. Perhaps changes in the numerical relationships between molecules of different size classes reflect the adaptability of plants through increased amplification of the desired genes.

In addition, the mitochondrial genome may contain plasmids, both linear and circular, with both DNA and RNA sequences, ranging in size from 1 to 30 kb. Mitochondrial plasmids likely originated from other cellular genomes or even other organisms. Sometimes their presence or absence can be associated with cytoplasmic male sterility of plants, but, however, not always. Plasmids are present in some species, but sterility is not observed. In at least one case, it was clearly demonstrated that in the mitochondria of lines with the so-called S-type of maize sterility, a correlation was found between the presence of plasmid-like mitochondrial DNA and the manifestation of the phenomenon of cytoplasmic male sterility. The ability of mitochondrial plasmids to integrate into both the mitochondrial genome and nuclear chromosomes was noted. However, in other cases, the presence of plasmid DNA does not always cause pollen sterility.

The size of the mitochondrial genome of plants is most variable - from 200 to 2500 kb. The size of the mitochondrial genome of higher plants is larger than the size of their chloroplast genome.

Significant variation in the size of the mitochondrial genome is the second feature of the plant mitochondrial genome. The genome is not only very large, but can also be different, even among closely related species, and in some cases low variability can be observed - species of the genus Brassica, in others it is very large. The highest size variability is observed in pumpkin plants. Within this family, the size of the mitochondrial genome is most variable - from 330 kb. in watermelon up to 2500 kb. at the melon. Therefore, the share of mitochondrial DNA in the total volume of the plant genome can also vary significantly - about 1% in most plants, up to 15% in melon hypocotyl cells.

Various reasons have been attempted to explain the presence of large mitochondrial genomes.

The presence of additional genes or special sequences necessary for the functioning of mitochondria.

The presence of DNA that is used by the plant, but not as a coding one, but for some other function.

DNA that is not used for mitochondrial functioning is called “selfish” DNA.

Apparently, there is another possibility for increasing the size of the mitochondrial genome - these are sequences homologous to nuclear and chloroplast DNA. Sequences homologous to nuclear DNA, for example, in Arabidopsis account for up to 5% of the mitochondrial genome. Initially, the chloroplast genome sequence incorporated into the mitochondrial genome was discovered in maize. It included a region of about 14 kb containing altered chloroplast 16S-ribosomal RNA genes and a region of the large subunit RDPK/O. Subsequently, chloroplast insertions were discovered in the mitochondrial genome of many higher plant species. Typically, they make up 1-2% of mitochondrial sequences and include three major sequences.

The sequence is 12 kb long. from a reverse repeat of chloroplast DNA. It contains sequences for the 3" exon of four transfer RNAs and sequence 16 S ribosomal RNA.

A 1.9 to 2.7 kb sequence that completely encodes the large subunit of Rubisco.

Sequence no longer than 2 kb. In the chloroplast genome, this region encodes the 3" end of the 23S ribosomal RNA, 4.5S and 5S rRNA, as well as three transfer RNAs. Of all the chloroplast genome sequences that are present in the plant mitochondrial genome, only the transfer RNA sequences are actually transcribed .

Since the same chloroplast sequences are present in the mitochondrial genome of many plant species, it can be assumed that they have some functional significance. At the same time, their role, the mechanism of transfer and the timing of this transfer remain unknown. Did this transfer occur at a distant time in the evolution of the formation of a eukaryotic cell, or did the presence of chloroplast insertions in the mitochondrial genome indicate that this is a normal process of information exchange between organelles, which occurs now, or does it occur periodically in the relatively recent evolutionary time of the formation of specific species and plant genera?

In addition, some of the mitochondrial genome sequences are sequences homologous to viral ones.

To establish the number of genes in the genome of plant mitochondria that actually function, a number of researchers determined the number of translation products. It was shown that the number of detectable protein bands was the same even for plants with 10-fold differences in genome size. Although the methods used do not directly answer the question about the total number of genes in the mitochondrial genome, it is nevertheless interesting that the same number of translation products was identified in the analyzed angiosperm species and was close to the number of genes encoding proteins in animal and mitochondrial mitochondria. yeast.

For the first time, the complete nucleotide sequence of mitochondrial DNA in plants was determined in 1986 in one species - Marchantia ( Marchantia polymorpha), and later in Arabidopsis and several species of algae.

The mitochondrial DNA molecule in Marchantia has a size of 186,608 bp. It encodes genes for 3 rRNAs, 29 genes for 27 tRNAs and 30 genes for known functional proteins (16 ribosomal proteins, 3 subunits of cytochrome C oxidase, cytochrome b, 4 subunits of ATP synthetase and 9 subunits of NADH dehydrogenase). The genome also contains 32 unidentified open reading frames. In addition, 32 introns were found located in 16 genes. The number of genes for a particular complex may vary in different plants, since one or more genes of this complex may be transferred to the nucleus. Among the unidentified genes, at least 10 are consistently found in almost all plant species, indicating the importance of their functions.

The number of mitochondrial genes encoding transfer RNAs of plant mitochondria is highly variable. In many species, their own mitochondrial transfer RNAs are clearly insufficient and are therefore exported from the cytoplasm (encoded by the nucleus or plastid genome). For example, in Arabidopsis, 12 transfer RNAs are mitochondrial encoded, 6 are chloroplast and 13 are nuclear; in Marchantia, 29 are mitochondrial and 2 are nuclear, and none of the transport RNAs have chloroplast coding; in potatoes, 25 are mitochondrial, 5 are chloroplast and 11 are nuclear; in wheat, 9 are mitochondrial, 6 are chloroplast and 3 are nuclear (Table 3).

Unlike animal mitochondrial DNA and chloroplast genes, plant mitochondrial DNA genes are dispersed throughout the genome. This applies to both genes encoding transfer RNAs and genes encoding proteins.

Table 3

The nature of mitochondrial transfer RNAs in plants

	Number of transfer RNAs encoded by genomes
		organelles
	mitochondria	chloroplasts
Arabidopsis
Marchantia
Potato

	Undefined	Undefined
Sunflower			Undefined
			Undefined
Corn			Undefined

Like the genome of fungal mitochondria, the genome of plant mitochondria has introns that the genomes of animal mitochondria do not have.

In some species, a number of genes in the genome are duplicated. Thus, in corn and broad beans, rRNA genes are not repeated, but in wheat they are repeated several times. Genes encoding mitochondrial proteins may also be repeated in their genome.

Naturally, mitochondria, like chloroplasts, contain much more enzyme proteins than their genome of genes. And, therefore, most proteins are controlled by the nuclear genome, assembled in the cytoplasm on cytoplasmic rather than mitochondrial ribosomes, and transported into mitochondrial membranes.

Thus, the mitochondrial genome of plants is an extremely variable system in structure, but quite stable in the number of genes. In contrast to the compact genome of chloroplasts, in the mitochondrial genome of plants, genes make up less than 20% of the genome. The enlargement of the mitochondrial genome compared to fungi or animals is caused by the presence of introns, various repeating sequences, insertions from the genome of chloroplasts, the nucleus and viruses. The functions of approximately 50% of the plant mitochondrial genome have not yet been elucidated. In addition to the fact that many structural genes that control the function of mitochondria are located in the nucleus, many genes that control the processes of transcription, processing, and translation of mitochondrial genes are also located there. Consequently, mitochondria are even less autonomous organelles than plastids.

Literature

Main:

1. Alyokhina N.D., Balnokin Yu.V., Gavrilenko V.F. and others. Physiology of plants. Textbook for students. Universities. M.: Academy. 2005. 640 p.

Davydenko O.G. Non-chromosomal heredity. Minsk: BSU. 2001. 189 p.

3. Danilenko N.G., Davydenko O.G. Worlds of organelle genomes. Minsk: Technology. 2003. 494 p.

4. Ivanov V.I. and others. Genetics. M.: Akademkniga. 2006. 638 p.

5. Zhimulev I.S. General and molecular genetics. Novosibirsk: Sib. Univ. 2007. 479 p.

6. Singer M., Berg P. Genes and genomes. M.: Mir. 1998. T. 1-

7. Chentsov Yu. S. Introduction to cell biology. M.: Akademkniga. 2004. 495 p.

Additional:

1. Danilenko N.G. RNA editing: genetic information is corrected after transcription // Genetics. 2001. T. 37. No. 3. pp. 294-316.

Margelis L. The role of symbiosis in cell evolution. M.: Mir, 1983.

3. Odintsova M. S., Yurina N. P. Genome of protist mitochondria // Genetics. 200 T. 38. No. 6. pp. 773-778.

4. Odintsova M. S., Yurina N. P. Genome of plastids of higher plants and algae: structure and functions // Mol. Biol. 2003. T. 37. No. 5. P. 768-783.

5. Yurina N. P., Odintsova M. S. General features of the organization of the chloroplast genome. Comparison with the genomes of pro- and eukaryotes // Mol. Biol. 199 T. 36. No. 4. P. 757-771.

6. Yurina N. P., Odintsova M. S. Comparative characteristics of the structural organization of genomes of chloroplasts and plant mitochondria // Genetics. 1998. T. 34. No. 1. P. 5-2.

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On the importance of studying mitochondrial DNA. Mitochondrial DNA mutations Human mitochondrial DNA contains genes encoding

What are mitochondria called?

What is unique about mtDNA?

How is kinship determined?

What can be determined through genetic testing?

Mitochondrial diseases and their diagnosis

How is aging related to mitochondria?

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On the importance of studying mitochondrial DNA. Mitochondrial DNA mutations Human mitochondrial DNA contains genes encoding

What are mitochondria called?

What is unique about mtDNA?

How is kinship determined?

What can be determined through genetic testing?

Mitochondrial diseases and their diagnosis

How is aging related to mitochondria?

Send your good work in the knowledge base is simple. Use the form below

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