The concept of a gene. Structural and regulatory genes. Genomes and spacers. The concept of a gene, genetic code. The modern concept of the structure and function of a gene.

Gene- structural and functional unit of heredity of living organisms. A gene is a DNA sequence that specifies the sequence of a specific polypeptide or functional RNA. Genes (more precisely, gene alleles) determine the hereditary characteristics of organisms that are transmitted from parents to offspring during reproduction. Moreover, some organelles (mitochondria, plastids) have their own DNA, which is not part of the organism’s genome, which determines their characteristics.

Among some organisms, mostly unicellular, horizontal gene transfer is found that is not associated with reproduction.

The term "gene" was coined in 1909 by the Danish botanist Vilhelm Johansen.

The study of genes is the science of genetics, the founder of which is considered to be Gregor Mendel, who in 1865 published the results of his research on the inheritance of traits when crossing peas. The patterns he formulated were later called Mendel's Laws.

There is no consensus among scientists on what angle to look at the gene. Some scientists consider it as an informational hereditary unit, and the unit of natural selection is a species, group, population or individual. Other scientists, such as Richard Dawkins in his book The Selfish Gene, view the gene as the unit of natural selection, and the organism itself as survival machine genes.

Currently, in molecular biology it has been established that genes are sections of DNA that carry some kind of integral information - about the structure of one protein molecule or one RNA molecule. These and other functional molecules determine the development, growth and functioning of the body.

At the same time, each gene is characterized by a number of specific regulatory DNA sequences (English)Russian, such as promoters, which are directly involved in regulating the expression of the gene. Regulatory sequences can be located either in close proximity to the open reading frame encoding a protein, or the beginning of an RNA sequence, as is the case with promoters (the so-called cis cis-regulatoryelements), and over distances of many millions of base pairs (nucleotides), as in the case of enhancers, insulators and suppressors (sometimes classified as trans-regulatory elements, English. trans-regulatoryelements). Thus, the concept of a gene is not limited only to the coding region of DNA, but is a broader concept that also includes regulatory sequences.

Originally the term gene appeared as a theoretical unit for the transmission of discrete hereditary information. The history of biology remembers disputes about which molecules can be carriers of hereditary information. Most researchers believed that only proteins could be such carriers, since their structure (20 amino acids) allows the creation of more variants than the structure of DNA, which is composed of only four types of nucleotides. Later it was experimentally proven that it is DNA that includes hereditary information, which was expressed as the central dogma of molecular biology.

Genes can undergo mutations - random or targeted changes in the sequence of nucleotides in the DNA chain. Mutations can lead to a change in the sequence, and therefore a change in the biological characteristics of a protein or RNA, which, in turn, can result in a general or local altered or abnormal functioning of the body. Such mutations in some cases are pathogenic, since they result in disease, or lethal at the embryonic level. However, not all changes in the nucleotide sequence lead to changes in protein structure (due to the effect of degeneracy of the genetic code) or to a significant change in the sequence and are not pathogenic. In particular, the human genome is characterized by single nucleotide polymorphisms and copy number variations. copynumbervariations), such as deletions and duplications, which account for about 1% of the entire human nucleotide sequence. Single nucleotide polymorphisms, in particular, define different alleles of a single gene.

The monomers that make up each of the DNA chains are complex organic compounds that include nitrogenous bases: adenine (A) or thymine (T) or cytosine (C) or guanine (G), the pentaatomic sugar pentose deoxyribose, named after and the DNA itself, as well as the phosphoric acid residue, was named. These compounds are called nucleotides.

Genes and memes

By analogy with genes, Richard Dawkins coined the term “meme” - a unit of cultural information. If a gene spreads in a chemical environment, using chemicals for reproduction, then a meme spreads in an information environment: on storage media, in human memory, and also on the network. Just as genes compete with each other for resources: chemical substances, so memes compete for information space. For a variety of reasons, fairly strong correlations can be observed between the spatial distribution of genes and memes.

Gene properties

2. discreteness - immiscibility of genes;

3. stability - the ability to maintain structure;

4. lability - the ability to mutate many times;

5. multiple allelism - many genes exist in a population in multiple molecular forms;

6. allelicity - in the genotype of diploid organisms there are only two forms of the gene;

7. specificity - each gene encodes its own trait;

8. pleiotropy - multiple effect of a gene;

9. expressiveness - the degree of expression of a gene in a trait;

10. penetrance - the frequency of manifestation of a gene in the phenotype;

11. amplification - increasing the number of copies of a gene.

Classification

Depending on the functions they perform, genes are divided into

1. Structural genes - genes that control the synthesis of structural proteins or enzymes

2. Regulatory genes – genes that control the synthesis of various proteins that affect the activity of structural genes. Regulatory genes, in turn, are divided into:

Genes are modifiers - they increase and decrease the activity of structural genes.

Suppressor genes - suppressing the activity of structural genes

According to their influence on the viability of organisms, genes are divided into:

1 Lethal genes are genes that lead to the death of their carriers

2. Sublital genes - genes leading to impaired reproductive function (sterility, reduced viability or non-viability of offspring) of their carriers

3. Neutral genes - those that do not affect the viability of the organism.

The structure of structural genes of prokaryotes and eukaryotes is specific. In prokaryotes, in most cases, the coding region is continuous; in eukaryotic genes, along with regions encoding a product specific to this gene (polypeptide, ribosomal RNA, transfer RNA), there are non-coding regions. The coding regions of the gene are, as already mentioned, called exons, and the non-coding regions are called introns. In a structural gene, exons alternate with introns. The gene seems to be torn apart.
The number and intragenic localization of introns are characteristic of each gene. The sizes of introns vary (from several tens to several thousand nucleotide pairs). Often, introns in a gene account for more nucleotides than exons. The role of introns is little studied. If they did not perform certain functions, were not needed by the body, they would be eliminated by natural selection.
The study of the gene continues. Modern information allows us to speak of a gene as a section of a genomic nucleic acid molecule that represents a unit of function and is capable of changing and acquiring various states through mutation and recombination. This is a complex, but functionally integral unit of heredity.

Eukaryotic genes, unlike bacterial ones, have a discontinuous mosaic structure. Coding sequences (exons) are interspersed with non-coding sequences (introns).

Related information.

REGULARITIES OF INHERITANCE AT THE ORGANISMAL LEVEL. MONOHYBRID CROSSING.

Genetic terminology

Among the biological sciences, genetics occupies a central place, since it studies the laws of heredity and variability that are universal for all living beings. All other properties (growth and development, metabolism, homeostasis, etc.) depend entirely on the material substrate of heredity - DNA.

Heredity– the property of living organisms to ensure structural and functional continuity between generations, as well as the specific nature of ontogenesis in certain environmental conditions. In the course of individual development, heredity determines the development and change in the morphological, physiological, biochemical and other characteristics of the organism. Hereditary continuity between generations guarantees the existence of a species over a certain historical period of time.

In order to fully determine the role of heredity, it is necessary to clearly understand:

1. Structural and functional organization of DNA

2. Patterns of transmission of hereditary information both in a series of generations,

and within the same organism

3. Mechanisms of regulation and control of cell vital processes

and individual development in general.

Variability– the property of living organisms to acquire new characteristics that distinguish them from their parent forms (structure and functions of organ systems and features of individual development).

Heredity and variability are two opposing but interrelated properties of an organism. The elementary unit of heredity and variability is gene(Greek “genos” - birth, forming). The term was proposed in 1909 by V. Johansen. Gene is a section of a DNA molecule that provides information about the synthesis of one polypeptide.

The main functions of DNA as a material carrier of heredity are: storage, reproduction and implementation of hereditary information.

Along with nuclear genes localized in chromosomes, heredity factors located in the cytoplasm were discovered. They are called plasmogens. It has been established that mitochondrial plastids contain DNA. The cytoplasm may contain foreign DNA from viruses and plasmids from bacteria. Extranuclear DNA is able to replicate independently of nuclear DNA. Cytoplasmic inheritance occurs along the maternal line, i.e. through the cytoplasm of the egg, because sperm do not contribute mitochondria to the zygote.

The criteria for cytoplasmic inheritance are:

Lack of quantitative Mendelian segregation in the offspring.

inability to detect clutch

different results of reciprocal crosses

The human mitochondrial genome is represented by a circular DNA molecule containing about 16.5 thousand nucleotide pairs, which includes r-RNA genes and 22 different t-RNAs. There is evidence that such developmental defects as non-fusion of the upper vertebral arches and fusion of the lower extremities are caused by mutations of mitochondrial genes.

Scheme of implementation of a gene into a trait:

Sign - any property or quality (biochemical, morphological, immunological, clinical, etc.) that allows one organism to be distinguished from another. The set of all internal and external characteristics of an organism that develop on the basis of the genotype under the influence of environmental factors is called phenotype.

Gene (section of a DNA molecule) → mRNA → protein (enzyme) → biochemical reactions → trait.

Thus, genes determine the development of specific traits. Since in the somatic cells of the body all chromosomes are paired - diploid set of chromosomes, therefore the genes are also paired - allelic genes. With the development of the chromosomal theory of heredity, it became clear that allelic genes are located in identical regions of homologous chromosomes and encode the same trait. An allele determines development options for the same trait.

Allelic genes are designated by one letter of the Latin alphabet: dominant(suppressive) allele – capital (A), and recessive(suppressed) – lowercase (a).

A pair of allelic genes may be the same (AA or aa), then they say that the individual homozygous on this basis. If the allelic genes in the pair are different (Ah) then an individual according to this trait heterozygous.

Gene properties:

- specificity(each structural gene has only its own inherent order of nucleotides and determines the synthesis of a specific polypeptide)

-integrity(when programming the synthesis of a polypeptide, the gene acts as an indivisible unit)

-discreteness(presence of subunits - nucleotides)

-stability(relatively stable)

-lability(capable of mutating)

Gene classification

The accumulation of knowledge about the structure, functions, nature of interaction and other properties of genes has given rise to several variants of gene classification.

1. By location of genes in cell structures distinguish between nuclei located in chromosomes - nuclear genes and cytoplasmic genes.

2. According to the location of genes in chromosomes differentiate allelic genes And nonallelic genes(genes located either in different loci of the same chromosome, or in chromosomes from different pairs. They are usually responsible for the development of different traits and are designated by different symbols).

3. According to functional significance differentiate structural genes, carry information about enzyme proteins and histones, and the sequence of nucleotides in various types of RNA. Among functional genes allocate modulator genes enhancing or weakening the effect of structural genes (inhibitors, integrators, modifiers) and genes regulating the functioning of structural genes ( regulators and operators).

4. By influence on physiological processes in the cell they distinguish lethal(the activity of these genes is incompatible with life), conditionally lethal ( reduce the vitality of the body) , proto-oncogenes – a group of genes that regulate normal cell division and cell differentiation. Modified by mutation, but active forms of proto-oncogenes are called oncogenes – capable of stimulating the development of tumor cells , the latter can also occur as a result of decreased activity antioncogenes(the products of these genes inhibit the mitotic activity of cells, participate in DNA repair and control the cell cycle).

Structural and functional levels of organization of hereditary material

Genomic level

Genome call the entire set (genes) of hereditary material contained in the haploid set of chromosomes of the cells of the body. During sexual reproduction, the genomes of two parental germ cells are combined during fertilization, forming genotype new organism. All somatic cells of such an organism have a double set of chromosomes. Each biological species is characterized by a certain number and structure of chromosomes, the totality of which constitutes the chromosome set, or karyotype(complete paired set of chromosomes, diploid set). All somatic cells, regardless of their origin and structure (with the exception of differentiated anucleate cells or polyploid cells), have not only the same number of chromosomes, but also an identical set of genes.

A characteristic feature of a karyotype is the presence of pairs of homologous chromosomes, in each pair one chromosome is of paternal origin, the other is of maternal origin. Homologous chromosomes are characterized by the same size and shape, as well as specific structure during differential staining.

In the diploid set, there are autosomes (for humans - chromosomes 1-22 pairs) and sex chromosomes.

Unlike somatic cells, germ cells contain a haploid set of chromosomes, which contains only one chromosome from each pair of chromosomes. In genetic terms, germ cells differ significantly from somatic cells:

1. During spermatogenesis, two types of sperm are formed: 50% contain the X chromosome and 50% Y chromosome (male body in humans heterogametic), during oogenesis, all eggs contain an X chromosome (female body homogametic)

2. Sex cells of one organism contain different genome, because the

As a result of crossing over, new combinations of non-allelic genes arise in the chromosome

Independent divergence of pairs of chromosomes (anaphase I of meiosis) leads to the emergence of various combinations of non-homologous chromosomes in gametes.

The random fusion of haploid cells during fertilization leads not only to the restoration of the diploid set, but also to the emergence of combinative variability.

Violations of the genomic level of organization of hereditary material, i.e. changes in the number of chromosomes in a diploid or haploid set are called genomic somatic or generative mutations.

1. Somatic mutations arise as a result of a violation of chromatid separation in anaphase of mitosis (heteroploidy) or disturbances of karyokinesis (polyploid cells appear) or cytokinesis (multinucleate cells appear).

2. Generative mutations arise as a result of a violation of the divergence of chromosomes (anaphase I of meiosis) or chromatids (anaphase II of meiosis) during the formation of germ cells. With these disorders, the formed gametes contain an altered haploid set of chromosomes.

A gene (ancient Greek γένος - genus) is a structural and functional unit of heredity of living organisms. A gene is a DNA sequence that specifies the sequence of a specific polypeptide or functional RNA. Genes (more precisely, gene alleles) determine the hereditary characteristics of organisms that are transmitted from parents to offspring during reproduction. Moreover, some organelles (mitochondria, plastids) have their own DNA, which defines them, and is not part of the organism’s genome.

At the same time, each gene is characterized by a number of specific regulatory DNA sequences, such as promoters, which are directly involved in regulating the expression of the gene. Regulatory sequences can be located either in close proximity to the open reading frame encoding a protein or the beginning of an RNA sequence, as in the case of promoters (the so-called cis-regulatory elements), or at a distance of many millions of base pairs (nucleotides), as in the case of enhancers, insulators and suppressors (sometimes classified as trans-regulatory elements). Thus, the concept of a gene is not limited only to the coding region of DNA, but is a broader concept that also includes regulatory sequences.

Initially, the term gene appeared as a theoretical unit for the transmission of discrete hereditary information. The history of biology remembers disputes about which molecules can be carriers of hereditary information. Most researchers believed that only proteins could be such carriers, since their structure (20 amino acids) allows the creation of more variants than the structure of DNA, which is composed of only four types of nucleotides. Later it was experimentally proven that it is DNA that includes hereditary information, which was expressed as the central dogma of molecular biology.

Genes can undergo mutations—random or targeted changes in the sequence of nucleotides in a DNA chain. Mutations can lead to a change in the sequence, and therefore a change in the biological characteristics of a protein or RNA, which, in turn, can result in a general or local altered or abnormal functioning of the body. Such mutations in some cases are pathogenic, since they result in disease, or lethal at the embryonic level. However, not all changes in the nucleotide sequence lead to changes in protein structure (due to the effect of degeneracy of the genetic code) or to a significant change in the sequence and are not pathogenic. In particular, the human genome is characterized by single nucleotide polymorphisms and copy number variations, such as deletions and duplications, which account for about 1% of the entire human nucleotide sequence. Single nucleotide polymorphisms, in particular, define different alleles of a single gene.

Gene properties.

discreteness - immiscibility of genes;

stability - the ability to maintain structure;

lability - the ability to mutate repeatedly;

multiple allelism - many genes exist in a population in multiple molecular forms;

allelicity - in the genotype of diploid organisms there are only two forms of the gene;

specificity - each gene encodes its own trait;

pleiotropy - multiple effect of a gene;

expressivity - the degree of expression of a gene in a trait;

penetrance - frequency of manifestation of a gene in a phenotype;

amplification - increasing the number of copies of a gene.

Gene structure.

According to modern concepts, the gene encoding the synthesis of a certain protein in eukaryotes consists of several essential elements. First of all, this is an extensive regulatory zone that has a strong influence on the activity of the gene in a particular tissue of the body at a certain stage of its individual development. Next, directly adjacent to the coding elements of the gene, there is a promoter - a DNA sequence up to 80-100 nucleotide pairs long, responsible for binding the RNA polymerase that transcribes the gene. Following the promoter lies the structural part of the gene, which contains information about the primary structure of the corresponding protein. For most eukaryotic genes, this region is significantly shorter than the regulatory zone, but its length can be measured in thousands of nucleotide pairs.

An important feature of eukaryotic genes is their discontinuity. This means that the protein-coding region of the gene consists of two types of nucleotide sequences. Some - exons - are sections of DNA that carry information about the structure of a protein and are part of the corresponding RNA and protein. Others - introns - do not encode protein structure and are not included in the mature mRNA molecule, although they are transcribed. The process of cutting out introns - “unnecessary” sections of the RNA molecule and splicing exons during the formation of mRNA is carried out by special enzymes and is called Splicing (crosslinking, splicing). Exons are usually joined together in the same order as they appear in the DNA. However, not absolutely all eukaryotic genes are discontinuous. In other words, in some genes, like bacterial ones, there is complete correspondence of the nucleotide sequence to the primary structure of the proteins they encode. Thus, the eukaryotic gene is in many ways similar to the prokaryotic operon, although it differs from it in a more complex and extended regulatory zone, and also in the fact that it usually encodes only one protein, and not several, like the operon in bacteria.

21. A gene is a functional unit of heredity. Molecular structure of the gene in prokaryotes and eukaryotes. Unique genes and DNA repeats. Structural genes. The “1 gene - 1 enzyme” hypothesis, its modern interpretation.

A gene is a structural and functional unit of heredity that controls the development of a specific trait or property. Parents pass on a set of genes to their offspring during reproduction. The term "gene" was coined in 1909 by the Danish botanist Vilhelm Johansen. The study of genes is the science of genetics, the founder of which is considered to be Gregor Mendel, who in 1865 published the results of his research on the inheritance of traits when crossing peas. Genes can undergo mutations - random or targeted changes in the sequence of nucleotides in the DNA chain. Mutations can lead to a change in the sequence, and therefore a change in the biological characteristics of a protein or RNA, which, in turn, can result in a general or local altered or abnormal functioning of the body. Such mutations in some cases are pathogenic, since they result in disease, or lethal at the embryonic level. However, not all changes in the nucleotide sequence lead to changes in protein structure (due to the effect of degeneracy of the genetic code) or to a significant change in the sequence and are not pathogenic. In particular, the human genome is characterized by single nucleotide polymorphisms and copy number variations, such as deletions and duplications, which account for about 1% of the total human nucleotide sequence. Single nucleotide polymorphisms, in particular, define different alleles of a single gene.

In humans, as a result of deletion:

Wolf syndrome - a region is lost on large chromosome 4,

“Cry of the cat” syndrome - with a deletion in chromosome 5. Cause: chromosomal mutation; loss of a chromosome fragment in the 5th pair.

Manifestation: abnormal development of the larynx, cat-like cries in early childhood, retardation in physical and mental development.

The chromosome of any organism, be it a bacterium or a human, contains a long, continuous strand of DNA along which many genes are located. Different organisms differ dramatically in the amount of DNA that makes up their genomes. In viruses, depending on their size and complexity, the genome size ranges from several thousand to hundreds of nucleotide pairs. Genes in such simply arranged genomes are located one after another and occupy up to 100% of the length of the corresponding nucleic acid (RNA and DNA). For many viruses, the complete DNA nucleotide sequence has been established. Bacteria have a much larger genome size. E. coli has a single strand of DNA - the bacterial chromosome consists of 4.2x106 (degree 6) nucleotide pairs. More than half of this amount consists of structural genes, i.e. genes encoding certain proteins. The rest of the bacterial chromosome consists of nucleotide sequences that cannot be transcribed, the function of which is not entirely clear. The vast majority of bacterial genes are unique, i.e. presented once in the genome. The exception is the genes for transport and ribosomal RNAs, which can be repeated dozens of times.

The genome of eukaryotes, especially higher ones, sharply exceeds the size of the genome of prokaryotes and, as noted, reaches hundreds of millions and billions of nucleotide pairs. The number of structural genes does not increase very much. The amount of DNA in the human genome is sufficient to form approximately 2 million structural genes. The actual number is estimated at 50-100 thousand genes, i.e. 20-40 times less than what could be encoded by a genome of this size. Consequently, we have to admit the redundancy of the eukaryotic genome. The reasons for redundancy have now become largely clear: firstly, some genes and nucleotide sequences are repeated many times, secondly, there are many genetic elements in the genome that have a regulatory function, and thirdly, some DNA does not contain genes at all.

The eukaryotic genome is characterized by two main features:

1) Repetition of sequences;

2) Division by composition into various fragments characterized by a specific content of nucleotides;

Repeated DNA consists of nucleotide sequences of varying length and composition that occur several times in the genome, either in tandem repeated or dispersed form. DNA sequences that are not repeated are called unique DNA. The size of the portion of the genome occupied by repetitive sequences varies widely between taxa. In yeast it reaches 20%, in mammals up to 60% of all DNA is repeated. In plants, the percentage of repeated sequences can exceed 80%.

According to the mutual orientation in the DNA structure, direct, inverted, symmetric repeats, palindromes, complementary palindromes, etc. are distinguished. The length (in number of bases) of an elementary repeating unit, the degree of their repeatability, and the nature of distribution in the genome vary over a very wide range; the periodicity of DNA repeats can have a very complex structure, when short repeats are included in longer ones or border them, etc. . In addition, mirror and inverted repeats can be considered for DNA sequences. The human genome is 94% known. Based on this material, the following conclusion can be drawn: repeats occupy at least 50% of the genome.

STRUCTURAL GENES - genes encoding cellular proteins with enzymatic or structural functions. These also include genes encoding the structure of rRNA and tRNA. There are genes that contain information about the structure of the polypeptide chain, and ultimately, structural proteins. Such sequences of nucleotides one gene long are called structural genes. Genes that determine the place, time, and duration of activation of structural genes are regulatory genes.

Genes are small in size, although they consist of thousands of nucleotide pairs. The presence of a gene is established by the manifestation of the gene trait (the final product). A general diagram of the structure of the genetic apparatus and its operation was proposed in 1961 by Jacob and Monod. They proposed that there is a section of a DNA molecule with a group of structural genes. Adjacent to this group is a region of 200 nucleotide pairs - the promoter (the region adjacent to the DNA-dependent RNA polymerase). This region is adjacent to the operator gene. The name of the entire system is operon. Regulation is carried out by a regulatory gene. As a result, the repressor protein interacts with the operator gene, and the operon begins to work. The substrate interacts with the gene with regulators, and the operon is blocked. Feedback principle. Expression of the operon is incorporated as a whole. 1940 - Beadle and Tatum proposed a hypothesis: 1 gene - 1 enzyme. This hypothesis played an important role - scientists began to consider the final products. It turned out that the hypothesis has limitations, because All enzymes are proteins, but not all proteins are enzymes. Typically, proteins are oligomers - i.e. exist in a quaternary structure. For example, the tobacco mosaic capsule has more than 1200 polypeptides. In eukaryotes, gene expression (manifestation) has not been studied. The reason is serious obstacles:

Organization of genetic material in the form of chromosomes

In multicellular organisms, cells are specialized and therefore some genes are turned off.

The presence of histone proteins, while prokaryotes have “naked” DNA.

Histone and non-histone proteins take part in gene expression and participate in the creation of structure.

22. Classification of genes: structural genes, regulators. Properties of genes (discreteness, stability, lability, polyallelicity, specificity, pleiotropy).

Gene properties:

Discreteness - immiscibility of genes;

Stability - the ability to maintain structure;

Lability - the ability to mutate repeatedly;

Multiple allelism - many genes exist in a population in multiple molecular forms;

Allelicity - in the genotype of diploid organisms there are only two forms of the gene;

Specificity - each gene encodes its own trait;

Pleiotropy - multiple effect of a gene;

Expressiveness is the degree of expression of a gene in a trait;

Penetrance is the frequency of manifestation of a gene in a phenotype;

Amplification is an increase in the number of copies of a gene.

23. Gene structure. Regulation of gene expression in prokaryotes. Operon hypothesis.

Gene expression is the process during which the hereditary information from a gene (a sequence of DNA nucleotides) is converted into a functional product - RNA or protein. Gene expression can be regulated at all stages of the process: during transcription, during translation, and at the stage of post-translational modifications of proteins.

Regulation of gene expression allows cells to control their own structure and function and is the basis of cell differentiation, morphogenesis and adaptation. Gene expression is a substrate for evolutionary change, since control over the timing, location, and quantity of expression of one gene can have an impact on the functions of other genes throughout the organism. In prokaryotes and eukaryotes, genes are sequences of DNA nucleotides. Transcription occurs on the DNA matrix - the synthesis of complementary RNA. Next, translation occurs on the mRNA matrix - proteins are synthesized. There are genes encoding non-messenger RNA (eg, rRNA, tRNA, small RNA) that are expressed (transcribed) but not translated into proteins.

Studies on E. coli cells have revealed that bacteria have 3 types of enzymes:

constitutive, present in cells in constant quantities regardless of the metabolic state of the body (for example, glycolytic enzymes);

inducible, their concentration under normal conditions is low, but can increase 100Q times or more if, for example, a substrate of such an enzyme is added to the cell culture medium;

repressed, i.e. enzymes of metabolic pathways, the synthesis of which stops when the end product of these pathways is added to the growing medium.

Based on genetic studies of the induction of β-galactosidase, which is involved in E. coli cells, in the hydrolytic breakdown of lactose, Francois Jacob and Jacques Monod in 1961 formulated the operon hypothesis, which explained the mechanism of control of protein synthesis in prokaryotes.

In experiments, the operon hypothesis was fully confirmed, and the type of regulation proposed in it began to be called control of protein synthesis at the transcription level, since in this case the change in the rate of protein synthesis is carried out due to changes in the rate of gene transcription, i.e. at the stage of mRNA formation.

In E. coli, like other prokaryotes, DNA is not separated from the cytoplasm by a nuclear envelope. During the transcription process, primary transcripts are formed that do not contain nitrones, and mRNAs lack a “cap” and a poly-A end. Protein synthesis begins before the synthesis of its matrix ends, i.e. transcription and translation occur almost simultaneously. Based on the genome size (4 × 106 base pairs), each E. coli cell contains information about several thousand proteins. But under normal growth conditions it synthesizes about 600-800 different proteins, which means that many genes are not transcribed, i.e. inactive. Protein genes whose functions in metabolic processes are closely related are often grouped together in the genome into structural units (operons). According to the theory of Jacob and Monod, operons are sections of the DNA molecule that contain information about a group of functionally interrelated structural proteins and a regulatory zone that controls the transcription of these genes. The structural genes of an operon are expressed consistently, either they are all transcribed, in which case the operon is active, or none of the genes are “read,” in which case the operon is inactive. When an operon is active and all its genes are transcribed, a polycistronic mRNA is synthesized, which serves as a template for the synthesis of all proteins of this operon. Transcription of structural genes depends on the ability of RNA polymerase to bind to the promoter located at the 5" end of the operon before the structural genes.

The binding of RNA polymerase to the promoter depends on the presence of a repressor protein in a region adjacent to the promoter, which is called the “operator”. The repressor protein is synthesized in the cell at a constant rate and has an affinity for the operator site. Structurally, the promoter and operator regions partially overlap, so the attachment of the repressor protein to the operator creates a steric hindrance for the attachment of RNA polymerase.

Most mechanisms regulating protein synthesis are aimed at changing the rate of binding of RNA polymerase to the promoter, thus influencing the stage of transcription initiation. Genes that synthesize regulatory proteins can be removed from the operon whose transcription they control.

A gene is a structural and functional unit of heredity that controls the development of a specific trait or property. Parents pass on a set of genes to their offspring during reproduction.

Genome - the totality of all genes of an organism; its complete chromosome set.

The human genome is the genome of the biological species Homo sapiens. In a normal situation, most human cells should contain 46 chromosomes: 44 of them do not depend on sex (autosomal chromosomes), and two - the X chromosome and the Y chromosome - determine sex (XY - in men or XX - in women), these 46 chromosomes make up one genome. Chromosomes contain a total of approximately 3 billion base pairs of DNA, containing an estimated 20,000-25,000 genes.

Studying the mechanisms of regulation of gene function, French geneticists Jacob and Monod came to the conclusion that there are structural and regulatory genes.

Structural genes include genes that control (encode) the primary structure of matrix, or information, RNA, and through them the sequence of amino acids in synthesized polypeptides. Another group of structural genes consists of genes that determine the sequence of nucleotides in the polynucleotide chains of ribosomal RNA and transfer RNA, i.e. structural genes are responsible for transmitting the genetic code from one generation of cells to another, and also control the synthesis of proteins.

Regulatory genes control the synthesis of specific substances, so-called DNA-binding proteins, which regulate the activity of structural genes. Regulatory genes interact with structural genes and regulate all biochemical processes in the cell, thereby allowing it to adapt to changes in the environment, for example, changes in the quantity and quality of nutrients entering it. If the pericellular environment is stable, regulatory genes inhibit (repress) structural ones. If the state of the environment changes, structural genes are activated and thereby contribute to the cell’s adaptation to new conditions. Jacob and Monod called the set of structural and regulatory genes an operon, and the gene responsible for repression and activation - the operator gene.

Gene structure (genetic maps, non-coding regions). A genetic map is a diagram of the relative location of genes on chromosomes, which allows one to predict the nature of inheritance of the studied traits of organisms. One end of the chromosome is taken as zero, and the distance is measured from it in special units (morganids).

A DNA molecule can contain many genes. A gene is a section of a DNA molecule that occupies a strictly defined position on the chromosome and whose DNA sequence contains the information necessary for protein synthesis. The human genome includes, according to rough estimates, 50-100 thousand genes, each of which performs a specific function - encodes a specific protein (for example, enzymes or structural proteins of the cell) or an RNA molecule. Human genes vary greatly in size, from several hundred to several million base pairs. It is known that protein coding sequences occupy only about 10% of the genome. The remaining 90% comes from non-coding regions. Most genes consist of alternating coding (exons) and non-coding (nitrons) parts.

Genetic maps chromosomes are made up for each pair of homologous chromosomes. Clutch groups are numbered sequentially as they are discovered. In addition to the linkage group number, the full or abbreviated names of the mutant genes, their distances in morganids from one of the ends of the chromosome, taken as the zero point, as well as the location of the centromere are indicated. Compose Genetic maps chromosomes is possible only for objects in which a large number of mutant genes have been studied. In humans, out of the expected 23 linkage groups (23 pairs of chromosomes), only 10 have been identified, and a small number of genes are known in each group; the most detailed maps are compiled for sex chromosomes.

The non-coding regions between genes are called spacers. Non-coding regions contain sequences that regulate gene activity. However, the function of much of the non-coding DNA is unclear. The main “building material” of living organisms is protein. Human cells are capable of synthesizing about 100 thousand different proteins. A protein is a complex molecule consisting of one or more chains built from amino acid residues. The sequence of amino acids in a protein is encoded in the base sequence of the gene. Three consecutive nucleotides represent a codon, which determines which amino acid will be located at a given position in the protein.