Second, lateral chromatid conjugation. Cells that have polythene chromosomes lose their ability to divide, they are differentiated and actively secrete, that is, polytenization of chromosomes is a way to increase the number of copies of genes for the synthesis of a product. Polytene chromosomes can be observed in Diptera, in plants in cells associated with the development of the embryo, in ciliates during macronucleus formation. Polytene chromosomes increase significantly in size, which makes them easier to observe and which made it possible to study the activity of genes as early as the 1930s. The fundamental difference from other types of chromosomes is that polytene chromosomes are interphase, while all the others can only be observed during mitotic or meiotic cell division.

A classic example is the giant chromosomes in the cells of the salivary glands of larvae. Drosophila melanogaster. DNA replication in these cells is not accompanied by cell division, which leads to the accumulation of newly built DNA strands. These threads are tightly interconnected along the length. In addition, somatic synapsis of homologous chromosomes occurs in the salivary glands, that is, not only sister chromatids conjugate with each other, but also the homologous chromosomes of each pair conjugate with each other. Thus, in cells salivary glands haploid number of chromosomes can be observed.

Story

The term "polytene chromosome" was proposed by P. Koller ( P. Koller) in 1935, and finally introduced into science by S. Darlington in 1937.

Dimensions

Polytene chromosomes are many times larger than the chromosomes of ordinary somatic cells. They are usually 100-200 times longer and 1000 times thicker (containing up to 1000 chromosomes) than the chromosomes of many interphase cells (both sex and somatic). Yes, in larvae D.melangaster the total length of four pairs of chromosomes in the salivary glands is 2000 microns, and in ordinary somatic cells this value is 7.5 microns.

Structure

striation

The characteristic shape and size of polytene chromosomes are achieved due to their maximum despiralization and multiple reproduction of chromosomes without their subsequent divergence, that is, they are formed as a result of endomitosis.

Polytene chromosomes have a characteristic transverse striation due to the presence of areas of denser spiralization of chromonemes - chromomeres. Dark areas (i.e., chromomeres) contain coiled, inactive chromatin, while light bands indicate an area with increased transcriptional activity. A clear distinction between dark discs and light interdiscal areas is explained by non-disjunction of child chromonemes. For this reason, all the features of a separate chromonema, including the chromomeric pattern, become more pronounced.

Essentially, polytene chromosomes are a pair of giant homologous chromosomes in a state of perfectly precise somatic conjugation. In this case, the disks and interdisk regions of the homologues are located strictly parallel and closely spaced. Such conjugation is not characteristic of the vast majority of somatic cells.

The polytene chromosome map was first compiled in 1935 by Calvin Bridges, and it is still widely used today.

The uniqueness of the structure of polytene chromosomes, namely the ability to clearly distinguish the details of their structure, was used by T. Paytner to study their rearrangements and the nature of conjugation. In general, the striation of polytene chromosomes is extremely useful for research; in particular, visualization of active and inactive chromatin regions was obtained using the example of polytene chromosomes. They can also be used to study the general structure of chromatin.

In addition, polytene chromosomes help identify larvae of bell mosquitoes ( Chironomid), which are otherwise difficult to distinguish.

Puffs

In polytene chromosomes, the transcription process is accompanied by the formation of the so-called. poufs- characteristic swellings of certain disks, which are formed as a result of local decompactization of DNA in them. Active transcription in these regions is indicated by the active incorporation of 3 H-uridine in the puff region. Large puffs are called Balbiani rings(in some sources, the terms "pouf" and "Balbiani rings" are used as synonymous).

Thus, the formation of puffs is a prime example differential transcription. Other famous example This process is the formation of lampbrush chromosomes.

Functions

Polytene chromosomes contain a large number of copies of genes, which greatly enhances gene expression. This, in turn, increases the production of essential proteins. For example, in the cells of the salivary glands of larvae D. melanogaster polytenization of chromosomes is necessary for the formation a large number sticky substance before pupation.

Notes

, With. 66-70.
, With. 69.
Balbiani E.G. Sur la structure du noyau des cellules salivaires chez les larves de Chironomus(fr.) // Zoologischer Anzeiger (English) Russian:magazine. - 1881. - Vol. 4 . - P. 637-641.

During the prophase of meiosis I, the synaptonemal complex retains parallel homologous chromosomes almost until they are built at the equator of the cell in metaphase I. Chromosomes are connected using the synaptonemal complex for some time (from 2 hours to 2-3 days in a person), the flow of which occurs between homologous chromosomes exchange of homologous DNA segments - crossing over. A synaptonemal complex is formed as a result of conjugation of homologous chromosomes.

Conjugation or synapsis is a pairwise contact of parallel and weakly condensed homologous chromosomes. Conjugation and formation of the synaptonemal complex (SC) is absent in lower fungus Aspergillusnidulans, Sc. Pombe and in some male flies, such as Drosophilamelanogaster.

Figure 2. Structure of the synaptonemal complex

After the premeiotic S-phase, the two sister chromatids of the chromosome form a common axial element. The axial elements of homologous chromosomes are included in the form of lateral (lateral) elements in the SC. A synaptonemal complex (SC) is formed - from the protein axes of two homologous chromosomes and the central element. The width of the side elements is 30-60 nm, the width of the central element is 60-120 nm. The lateral elements are composed of meiosis-specific proteins. Protein bridges are formed between them. The first specific SC protein (which appears in interphase) is the REC8 protein. The DNA of homologous chromosomes in the form of loops extends from the lateral (lateral) elements of the SC. Most of the DNA is localized outside the SC, only 0.5% of genomic DNA enters the SC, strongly binding to proteins. A small amount of DNA passes through the central space of the SC. SC DNA consists of unique and moderately repetitive sequences that can interact with SC proteins and proteins involved in recombination and segregation of homologous chromosomes.

90% of SC consists of proteins. Allocate 5-10 major proteins with a molecular weight of 26 to 190 kDa. In mammals, 3 SC proteins are well studied - SCP1, SCP2, CSP3 (synaptonemal complex protein). Yeast SC proteins were named Zip1, Zip2, Red1, Hop1.

The SCP1 protein is the main protein of the SC transverse filaments. The C-terminus of this protein is "anchored" on the lateral elements of the SC and interacts with DNA here, the N-terminus reaches the central space of the SC and connects the opposite lateral elements of the SC using protein-protein interactions.

In yeast, the Zip1 protein is the main protein in the SC transverse filaments. The Zip2 protein acts as a synapsis initiator by forming polymerization sites for the Zip1 protein.

Proteins SCP2, SCP3 are proteins of the lateral elements of the SC. They are jointly localized along the axial elements of the chromosomes and the lateral elements of the SC. After diplotenes are concentrated in the centromeres of chromosomes, although a small number of them are found along the arms of the chromosomes. That. these proteins are involved in the linkage - cohesion of sister chromatids. Mitosis-specific proteins - Smc1p, Smc3p, Scc1p, Scc3p - also belong to cohesin proteins.

In yeast, the Red1 protein forms centers for the formation of axial elements. It interacts with the Hop1 protein, which is also a component of the lateral elements of the SC in yeast.

The basis of extended lateral elements-- complex of the four cohesin proteins. On the eve of meiosis, a specific Rec8 cohesin protein appears in the chromosomes, which replaces the somatic cohesin Rad21. Then three other cohesin proteins, which are also present in somatic cells, are attached to it, but instead of the somatic cohesin SMC1, the meiosis-specific protein SMC1b appears (its N-terminus differs by 50% from the N-terminus of the somatic SMC1 protein). This cohesin complex sits within the chromosome between two sister chromatids, holding them together. The cohesin complex binds meiosis-specific proteins, which become major proteins of chromosome axes and turn them into lateral elements of the synaptonemal complex.

The regulation of protein assembly in SC occurs via phosphorylation-dephosphorylation. Many SC proteins contain several sites of phosphorylation by protein kinase p34.

Recombination nodules are distinguished within the SC: the early ones are at the leptotene and zygotene stages and are localized in the lateral elements of the SC at the sites of recombination initiation. The composition of early recombination knots includes enzymes that are necessary to initiate double-strand breaks in DNA and form single-strand ends. For example, the Spo11p protein (topoisomerase) is the main meiosis-specific endonuclease that performs double breaks in DNA. Late recombination nodules were found at the pachytene stage, localized in the central element of the SC. A relationship was found between the number and distribution of late recombination nodules and the number and distribution of chiasmata in the bivalent. Thus, late nodules are multienzyme complexes that catalyze crossing over.

The initiation of SC formation in yeast and plants occurs at several points along the entire length of the bivalent (6 initiation sites in corn, up to 36 in lily); in animals, SC formation begins with telomeres and spreads like a zipper. Completion of the formation of SC - pachytene, its destruction - diplotene.

SC functions: - keeps homologous chromosomes strictly opposite each other;

prevents adhesion of homologous chromosomes - reversible conjugation;

necessary precondition for crossover.

Mutants with no conjugation also lack crossing over.

Genetic control of conjugation

Rye. 3 groups of recessive mutations that disrupt the formation of SC.

strong synapsis mutations. Mutations block the conjugation of chromosomes during the transition from leptotene to zygotene.

Mutations of weak asynapsis or desynapsis are the most numerous group. In rye, these mutations disrupt conjugation in 1–3 pairs of chromosomes out of 7. Both divalents and univalents are observed; suppression of SC formation at the ends of chromosomes; internal areas of asynapsis or desynapsis. The frequency of occurrence of chiasmata, the frequency of crossing over decreases.

Indiscriminate synapsis mutations - the simultaneous presence of a homologous and non-homologous synapsis, which leads to the appearance of multivalents and univalents. The lateral elements of the SC can form folds due to synapsis "on itself".

Synapsis of X and Y chromosomes

In the mole vole (a genus of voles), the X and Y chromosomes form a short SC in the early pachytene (they conjugate with short arms), desynapsis occurs in the diplotene, and the sex chromosomes become univalent.

For the XY-bivalent of most mammals, terminal conjugation of the sex chromosomes (long arms of the X and Y chromosomes) is characteristic, the absence of which disrupts the divergence of the sex chromosomes during meiosis. The X and Y chromosomes are conjugated by a homologous region containing such genes as the gene for general color blindness, xeroderma pigmentosa, and hemorrhagic diathesis.

The XY-bivalent is switched off from the cell metabolism by the formation of the sexual vesicle, inside which the unconjugated regions of the chromosomes are in a condensed state.

The X chromosome can be associated with aberrant chromosomes (translocated, inverted). This is a protective mechanism - if the X chromosome is closely associated with an aberrant one, then a sexual vesicle does not form around the sexual bivalent. This serves as a signal to stop meiosis at the pachytene stage. This prevents damaged chromosomes from entering the germ cells.

Parthenogenesis.

General characteristics of germ cells, or gametes.

7. Law of splitting. dominance and recessiveness.

8. The law of purity of gametes. Analyzing cross.

3 parts yellow wrinkled seeds, 3 parts green smooth seeds and 1 part green wrinkled seeds.

Gene-controlled x- and y-chromosomes of a person.

The linear arrangement of genes on chromosomes. Genetic and cytological maps of chromosomes.

Non-allelic genes in the determination of traits.

multiple alleles. Inheritance of blood groups according to the avo system.

Complementarity. position effect.

Polymerism. Polygenic inheritance as a mechanism for the inheritance of quantitative traits.

Quantitative and qualitative specifics of gene manifestation in traits: penetrance, expressivity, gene field of action, pleiotropy, genocopies.

Transfer of biological information to protein (translation). Structure, types and role of RNA.

The hypothesis "one gene - one enzyme", its modern interpretation..

5. Regulation of gene expression in prokaryotes and eukaryotes.

Gene mutations. The concept of gene diseases.

Antimutational barriers of the body.

Repair of genetic material. .

Gene diseases, mechanisms of their development, inheritance, frequency of occurrence.

1. Structural mutations of chromosomes (chromosome aberrations).

Duplications, inversions, circular chromiums. Origin mechanism. phenotypic expression.

Translocations, their essence. Reciprocal translocations, their characteristics and medical significance. Robertsonian translocations and their role in hereditary pathology.

radiation mutations. Genetic danger of environmental pollution.

Aneuploidy.

4. Medical genetic counseling.

5. Prenatal diagnosis:

Stage 2 - activation of gametes, occurs after their contact. The activation of the spermatozoon is called the acrosomal reaction. Egg activation is a cortical reaction.

General characteristics of gastrulation. Features of gastrulation in amphibians and birds. Gastrulation in higher (placental) mammals.

The role of heredity and environment in embryonic development.

Morphogenesis (shaping), its main processes:

5. Integration in development, integrity of ontogeny. The role of hormones in the coordination of developmental processes.

Biological aspects of aging and death.

Genetic control of growth. The role of the nervous and endocrine systems in the regulation of growth processes.

Aging as a continuation of development. Software theories of aging.

Processes leading to aging at different levels of the organization.

3. Reparative regeneration as a process of secondary development, its biological essence.

4. Characteristic signs of reparative regeneration, atypical regeneration.

5. The scale of regeneration, its boundaries in different animal species.

6. Methods of reparative regeneration: epimorphosis and morpholaxis.

7. Regeneration of organs and tissues in highly organized animals, humans.

8. Regenerative hypertrophy: molecular, cellular and systemic mechanisms.

9. Evolution of the regenerative capacity.

13. Regeneration of pathologically altered organs.

The body as an open self-regulating system. General (cybernetic) patterns of homeostasis of living systems.

4. Cellular mechanisms of homeostasis.

5. Systemic mechanisms of homeostasis:

1. Population structure of mankind. Demographic and genetic characteristics of the human population. Demos, isolates.

2. Drift of genes and features of gene pools of isolates.

3. Influence of the mutation process, migration, isolation, population waves on the genetic constitution of people.

4. The specifics of the action of natural selection in human populations. Selection against heterozygotes and homozygotes.

5. Selection and counter selection..

6. Genetic polymorphism of humanity.

And the circulatory systems of chordates.

The main evolutionary characteristics of organs and functions:

2. The main principles of the evolution of organs and functions:

Phylogeny of the respiratory organs of chordates

3. Phylogeny of the circulatory organs in chordates:

And the excretory system of chordates.

Phylogeny of the digestive system of chordates:

2. Phylogeny of the excretory system of chordates:

Definition and structure of ecology.

Environment as an ecological concept. Environmental factors.. The concept of ecological valence.

The concept of ecosystem, biogeocenosis, anthropobiogeocenosis.

Changes in biocenoses over time. ecological successions.

Biosphere as a natural-historical system. Modern concepts of the biosphere. .

Living matter: quantitative and qualitative characteristics. Role in the nature of the planet.

Functions of the biosphere in the development of the nature of the Earth.

Cycle of chemical elements as the main function of the biosphere.

Evolution of the biosphere.

Increasing human influence on the biosphere. Environmental consequences.

The emergence and development of the noosphere.

The subject and tasks of human ecology.

General characteristics of the human environment.

3. The concept of an adaptive type.

4. Man as a creative ecological factor. anthropogenic ecosystems.

12 species of European butterflies, and some species of other insects, have switched to feeding on the petals of its flowers and budley seeds.

5. Human adaptation to the environment: biological and social aspects.

6. Problems of environmental protection and rational nature management.

8. Cytoplasm: ground substance, cytoskeleton, organelles.

The main substance of the cytoplasm is represented by hyaloplasm. This is a colloidal solution of inorganic and organic substances, especially a lot of proteins in the hyaloplasm.

Hyaloplasm functions:

connection of the components of the cytoplasm into a single whole

participation in the transport of substances

glycolysis occurs in the hyaloplasm

ATP and inclusions accumulate in the hyaloplasm.

cytoskeleton cells are represented by microtubules and microfilaments.

Each microtubule is a hollow cylinder 20–30 nm in diameter, formed by the protein tubulin. Microtubules play the role of a cytoskeleton, because pervade the entire cytoplasm of the cell. In addition, microtubules are involved in the creation of the cell center and in the transport of substances within the cell.

Microfilaments are protein filaments about 4nm thick. Most of them are formed by actin molecules, of which about 10 species have been identified. They can be grouped into bundles that form the supporting structures of the cytoskeleton.

microtubules- tubular formations of a protein nature of various lengths with an outer diameter of 24 nm. Microtubules are found in a free state in the cytoplasm of cells or as structural elements of flagella, cilia, mitotic spindle, centrioles.

Animal cell organelles: EPS, Golgi apparatus, lysosomes, mitochondria, plastids, ribosomes, cell center.

Cell organelles are divided into general-purpose and special-purpose organelles.

Special purpose organelles are found only in specialized cells and ensure that these cells perform specific functions. These include the myofibrils of the muscle cell, the ciliary epithelium of the respiratory tract, the villi of the small intestine, and the sperm flagellum.

General purpose organelles are inherent in all cells. These include the endoplasmic reticulum, lysosomes, mitochondria, ribosomes, the Golgi complex, the cell center, microtubules and microfilaments, and plastids (the latter only in plants).

Endoplasmic reticulum represented by a network of channels and flattened cisterns bounded by a single membrane. It branches throughout the cytoplasm, which allows it to perform the following functions:

mechanical - ensuring a constant shape of the cell;

increase in the area of the inner surface of the cell;

transport - the transfer of substances between the organelles of the cell, the organelles and the nucleus, the cell and the external environment;

EPS is divided into two types: rough and smooth. Rough has numerous ribosomes on the outer surface, on which protein is synthesized. A smooth network consists of channels and tanks of a smaller cross section than in a rough EPS. It performs the following functions:

synthesis of lipids that make up membranes;

neutralization of harmful metabolic products;

synthesis of precursors of steroid hormones;

Lysosome. This is a bubble with a diameter of 0.2 - 0.5 microns, covered with a single-layer membrane. This membrane protects the structures and substances of the cell from the destructive action of lysosome enzymes. If its integrity is violated, the enzymes enter the cytoplasm of the cell, and autolysis- self-digestion of the cell. Lysosome enzymes are able to break down proteins, nucleic acids, polysaccharides and lipids.

Functions of lysosomes:

1. carry out intracellular digestion; lysosomes - the miniature digestive system of the cell;

2. remove obsolete cell organelles or larval organs. So, the tail of the frog tadpole is resorbed under the action of the enzyme lysosomes - cathepsin;

3. convert substances harmful to the cell into digestible products;

4. participate in the protection of the cells of bacteria and viruses (viruses are immured in the lysosome).

Lysosomes are formed in the Golgi complex: enzymes synthesized on ribosomes enter here, here they are surrounded by a membrane and excreted into the cytoplasm. These are the primary (inactive) lysosomes. Secondary (active) lysosomes are formed from primary ones. They are subdivided into phagolysosomes And autolysosomes. Phagolisosomes digest material that enters the cell from outside. Autolysosomes destroy their own, worn-out cell structures. Secondary lysosomes, in which the digestion process is completed, are called residual little bodies. They lack enzymes and contain undigested material.

Mitochondria(1-5 microns) - a two-membrane organoid that performs the function of an intracellular energy station. These are rounded formations, limited by two membranes - outer and inner. The outer membrane is smooth, it regulates both the entry of substances into the mitochondria and their removal. The inner membrane forms folds - cristae, facing inside the mitochondria. Inside the mitochondria there is a so-called matrix containing various enzymes, Ca 2+ and Mg 2+ ions, as well as DNA, t-RNA, i-RNA and ribosomes (moreover, DNA and ribosomes in mitochondria are similar to those of bacteria).

Due to the presence of its own DNA (1 ring-shaped molecule), mitochondria can multiply regardless of cell division. This happens by ligation of the original mitochondria. They double the amount of DNA first. Due to the content of t-RNA, i-RNA and ribosomes, mitochondria can synthesize their own protein.

In addition, mitochondria play a role in the transmission of traits by inheritance (cytoplasmic inheritance).

On the cristae of mitochondria, redox processes occur, accompanied by the release of energy. It is used to form phosphate bonds in ATP. The accumulation of ATP makes mitochondria a kind of accumulator of cell energy, which is spent on the life processes of the cell as needed. Due to intensive work, mitochondria have a short lifespan, for example, mitochondria of liver cells live only 10 days.

golgi apparatus is a system dictyosome number from several tens to several hundreds and even thousands per cell. Each dictyosome is formed by a stack of 3-12 large saucer-like cisterns. Tubes and vesicles having a membrane structure depart from the tanks in all directions. The tubules connect individual tanks of adjacent stacks, so they are formed single network. Vesicles are involved in the formation of primary lysosomes. IN different types cells, the Golgi apparatus occupies a strictly defined position, near the nucleus.

The functions of the Golgi apparatus are diverse:

1. the formation of primary lysosomes, which then enter the cytoplasm;

2. packaging of proteins coming from the ER for subsequent export from the cell;

3. synthesis structural components cells, such as collagen filaments;

4. synthesis of fats and polysaccharides that make up cell membranes;

Ribosome(0.02-0.03 µm) is a non-membrane organelle that performs protein biosynthesis. The ribosome consists of two unequal subunits, large and small. Both subunits are formed in the nucleolus, but they unite into the ribosome only at the moment of attachment to the mRNA. This process occurs with the help of Mg 2+ ions.

Each cell contains from tens of thousands to millions of ribosomes. Some of them are in a free state, but most of the ribosomes are attached to the ER membranes. The former synthesize proteins used for the needs of the cell, the latter synthesize proteins "for export". They enter the Golgi complex through the ER channels, are packed into membranes, and then are removed from the cell. The speed of ribosomes is amazing - one medium-sized protein molecule is synthesized in one minute. This allows you to continuously update the body's proteins, which wear out in the course of its life. So, human liver proteins are updated in 7 days.

Cell Center- a non-membrane organelle in which microtubules are formed from tubulin protein. The cell center consists of two centrioles located perpendicular to each other. Each centriole is a tank made up of 9 microtubules. Microtubules are interconnected by a system of ligaments, and outside they are dressed with a protein sheath. Centrioles double before cell division. During mitosis, centrioles determine the locations of the spindle poles. Moreover, the position of centrioles in a dividing cell determines the centers of new cells. The core will be located here, because. the cell center is always located near the nucleus.

9. Inclusions

It is a non-permanent component of the cytoplasm. Their presence and quantity depends on the intensity of metabolism and the state of the organism. They are divided into three groups:

1. reserve nutrient material (glycogen, fat, starch);

2. substances to be removed from the cell (enzymes, hormones);

3. ballast substances (pigments, salts of oxalic acid). They are more typical for plant cells, because. plants do not have systems analogous to the excretory system of animals.

LECTURE 2 Cell nucleus. The hereditary apparatus of human cells.

1. Structure and functions of the nucleus.

The nucleus is located either in the center of the cell or is displaced to the periphery. The nucleus of a eukaryotic cell has its own membrane that separates it from the cytoplasm. The membrane has 2 layers, between them there is a perinuclear space associated with EPS.

The nuclear membrane has holes - pores. But they are not through, but filled with special proteins. Through the pores, RNA molecules exit the nucleus into the cytoplasm, and proteins move towards them into the nucleus. The nuclear envelope membrane itself ensures the passage of low molecular weight compounds in both directions. The inner membrane of the nuclear envelope has a protein lining to which chromosomes are attached. This ensures their orderly arrangement.

Functions of the nuclear envelope: protective, regulation of the transport of substances and organelles

Beneath the membrane is the nuclear sap karyoplasm. It contains one or more nucleoli, a significant amount of RNA and DNA, various proteins, incl. most nuclear enzymes, as well as free nucleotides, amino acids, metabolic intermediates. Karyoplasm carries out the interconnection of all nuclear structures.

Nucleoli are rounded, strongly compacted areas of the cell nucleus with a diameter of 1-2 microns or more that are not limited by the membrane. The shape, size and number of nucleoli depend on functional state nuclei: the larger the nucleolus, the higher its activity. Their nucleus can contain from 1 to 10, and they are absent in yeast nuclei.

During nuclear division, the nucleoli are destroyed. At the end of division, they are again formed around certain parts of the chromosome (nucleolar organizers) located in the region of the secondary chromosome constriction. The function of the nucleoli is to synthesize

rRNA and assembly of ribosome subunits from protein and rRNA.

Polytene chromosomes have a characteristic transverse striation due to the presence of areas of denser spiralization of chromonemes - chromomeres. Dark areas (i.e., chromomeres) contain coiled inactive chromatin, while dark bands indicate an area with increased transcriptional activity. A clear distinction between dark discs and light interdiscal areas is explained by non-disjunction of child chromonemes. For this reason, all the features of a separate chromonema, including the chromomeric pattern, become more pronounced.

In fact, polytene chromosomes are a pair of giant homologous chromosomes in a state of perfectly precise somatic conjugation. In this case, the disks and the interdisk regions of the homologues are located strictly parallel and closely spaced. Such conjugation is not characteristic of the vast majority of somatic cells.

Polytene chromosomes were first mapped in 1935 by Calvin Bridges. Calvin B. Bridges), and it is widely used to this day.

In addition, polytene chromosomes help identify larvae of bell mosquitoes ( Chironomid), which are otherwise difficult to distinguish.

Puffs

Puffing is characteristic of the larval stage. The formation and disappearance of puffs is regulated internal environment organism according to the stage of development. One of the most important regulators of the formation of puffs in insects are steroid hormones, in particular, the molting hormones - ecdysone. The influence of proteins synthesized by earlier puffs on the development of later puffs was also revealed.

Thus, the formation of puffs is a prime example differential transcription. Another well-known example of this process is the formation of lampbrush chromosomes.

Functions[

In addition to increasing the size of the nucleus and the size of the cell, polytene chromosomes, since they contain a large number of copies of genes, increase their expression. This, in turn, increases the production of proteins needed by the specialized cell. For example, in the cells of the salivary glands of larvae D. melanogaster Chromosomes undergo many rounds of endoreduplication to form large amounts of adhesive prior to pupation.

In other cases, tandem duplication of sites located near the centromere of the X chromosome, observed in the cells of the salivary glands and intestines, leads to the occurrence of a mutation bar, manifested in a change in the shape of the eye.

homologous chromosomes- a pair of chromosomes of approximately equal length, with the same position of the centromere and giving the same picture when stained. Their genes in the corresponding (identical) loci are allelic genes - alleles, i.e. code for the same proteins or RNA. In bisexual reproduction, one homologous chromosome is inherited by the organism from the mother, and the other from the father.

In the course of DNA duplication in the S-phase of the interphase preceding mitosis, two identical chromatids are formed that carry the same genetic material. Subsequently, one such chromatid from a pair of chromatids of a given chromosome enters each daughter cell. As a result, the daughter cell turns out to be an exact genetic copy of the mother cell (this, however, does not apply to cases where various mutations and rearrangements take place) and has the same number of chromosomes as the mother cell.

In diploid ( 2n) of organisms, the genome is represented by pairs of homologous chromosomes. In meiosis, homologous chromosomes exchange their parts. This phenomenon underlies the recombination of genetic material and is called crossing over.

Homologous chromosomes are not identical to each other. They have the same set of genes, however, they can be represented by both different (in heterozygotes) and the same (homomozygotes) alleles, that is, forms of the same gene responsible for the manifestation various options the same sign. In addition, as a result of some mutations (duplications, inversions, deletions and translocations), homologous chromosomes may occur that differ in the sets or arrangement of genes.

diploid cells- these are living cells, in contrast to haploid cells (containing a half set), containing a complete set of chromosomes - one pair of each type. Most cells human body are diploid except for gametes.

Normal in life cycle the human body is the correct alternation of haploid and diploid phases of cell development. Haploid cells are formed as a result of meiosis and meiotic division of diploid cells. After that, cells can multiply by mitosis and mitotic divisions with the formation of a multicellular body consisting of diploid somatic cells and several generations of haploid germ cells (descendants).

Diploid cells are formed from haploid cells as a result of the sexual process (fertilization, fusion of germ cells, gametes) with the formation of a zygote.

Chromatin, its classification. The structure of chromosomes.
In the cell nucleus, small grains and clumps of material are found, which are stained with basic dyes and therefore was called chromatin (from the Greek chroma - paint).
Chromatin is a deoxyribonucleoprotein (DNP) and consists of DNA coupled to my-histone proteins or non-histone proteins. Histones and DNA are combined into structures called nucleosomes. Chromatin corresponds to chromosomes, which in the interphase nucleus are represented by long twisted threads and are indistinguishable as individual structures. The severity of spiralization of each of the chromosomes is not the same along their length. Implementation genetic information carry out despiralized sections of chromosomes.
Classification of chromatin. There are two types of chromatin:
1) euchromatin, located closer to the center of the nucleus, lighter, more despirilized, less compact, more functionally active. It is assumed that it contains the DNA that is genetically active in the interphase. Euchromatin corresponds to chromosome segments that are despiralized and open for transcription. These segments are not stained and are not visible under a light microscope.
2) heterochromatin- densely spiralized part of chromatin. Heterochromatin corresponds to condensed, tightly coiled chromosome segments (making them inaccessible to transcription). It is intensely stained with basic dyes, and in light microscope looks like dark spots, granules. Heterochromatin is located closer to the nuclear envelope, is more compact than euchromatin, and contains “silent” genes; genes that are currently inactive. Distinguish between constitutive and facultative heterochromatin. Constitutive heterochromatin never becomes euchromatin and is heterochromatin in all cell types. Facultative heterochromatin can be converted into euchomatin in some cells or at different stages of the organism's ontogeny. An example of an accumulation of facultative heterochromatin is the Barr body, an inactivated X chromosome in female mammals, which is tightly twisted and inactive in the interphase. In most cells, it lies near the karyolemma.
Thus, according to morphological features nucleus (according to the ratio of the content of eu- and heterochromatin), it is possible to assess the activity of transcription processes, and, consequently, the synthetic function of the cell. With its increase, this ratio changes in favor of euchromatin, with a decrease, the content of heterochromatin increases. With complete suppression of the functions of the nucleus (for example, in damaged and dying cells, with keratinization of the epithelial cells of the epidermis - keratinocytes, with the formation of blood reticulocytes), it decreases in size, contains only heterochromatin and is stained with basic dyes intensively and evenly. This phenomenon is called karyopyknosis (from the Greek karyon - core and pyknosis - seal).
Chromatin and chromosomes are deoxyribonucleoproteins (DNPs), but chromatin is an untwisted state and chromosomes are a twisted state. There are no chromosomes in the interphase nucleus; they appear as chromosomes when the nuclear membrane is destroyed (during division).
The distribution of heterochromatin (the topography of its particles in the nucleus) and the ratio of the content of eu- and heterochromatin are characteristic of cells of each type, which makes it possible to identify them both visually and using automatic image analyzers. At the same time, there are certain general regularities in the distribution of heterochromatin in the nucleus: its accumulations are located under the karyolemma, interrupted in the pore area (due to its connection with the lamin) and around the nucleolus (perinucleolar heterochromatin), smaller clumps are scattered throughout the nucleus .
The structure of chromosomes
Chromosomes are the most packed state of chromatin. The most compact chromosomes are seen at the metaphase stage, and they consist of two chromatids connected at the centromere.

The role of positive and negative feedbacks is different. Negative feedbacks ensure the stability of the functions of living systems, their resistance to external influences. They are the main mechanism of energy and metabolic balance in living systems, population control, self-regulation evolutionary process. Positive feedbacks play a positive role of enhancers of vital processes. They play a special role in growth and development. Consider them in more detail.

Negative feedback (NFB) is a type of feedback in which the input signal to the system is changed in such a way as to counteract the change in the output signal.

Negative feedback makes the system more resistant to random parameter changes.

Negative feedback is widely used by living systems different levels organizations - from cells to ecosystems - to maintain homeostasis. For example, in cells, on the principle of negative feedback, many mechanisms for regulating the work of genes are based, as well as the regulation of the work of enzymes (inhibition of the metabolic pathway by the end product). In the body, the system of hypothalamic-pituitary regulation of functions is based on the same principle, as well as many mechanisms of nervous regulation that support individual parameters of homeostasis (thermoregulation, maintaining a constant concentration of carbon dioxide and glucose in the blood, etc.). In populations, negative feedbacks provide abundance homeostasis. The physiological meaning of negative feedback lies in the fact that an increase in a regulated value (for example, the activity of an organ) above a certain limit causes a lowering effect on the part of the subsystem associated with it; a sharp decrease in the controlled value causes the opposite effect.

Negative feedback also keeps the human body temperature around 37 C.

Man and all living beings, being self-regulating homeostatic systems, live mainly due to negative feedback.

Positive feedback (PFC) is a type of feedback in which a change in the output signal of the system leads to such a change in the input signal, which contributes to a further deviation of the output signal from its original value.

Positive feedback speeds up the response of the system to a change in the input signal, so it is used in certain situations where a quick response is required in response to a change in external parameters. At the same time, positive feedback leads to instability and the emergence of qualitatively new systems called generators (producers).

Positive feedback mismatches the system, and, ultimately, the existing system is transformed into another system, which is more stable (that is, negative feedbacks begin to act in it).

The action of the non-linear positive feedback mechanism leads to the fact that the system begins to develop in the blow-up mode.

Positive feedback plays important role in macroevolution. In general, in macroevolution, positive feedback leads to a hyperbolic acceleration of development rates, which creates the effect of a uniform distribution of events on a logarithmic time scale.

At the level of the simplest microorganisms, which do not yet have nerve cells, the feedback channel (perception - response) existed and exists directly on the border separating external environment organism from the internal environment. Based on the now generally accepted theory of the origin of life, let's consider how the feedback worked at the prebiological level. For example: the simplest multimolecular systems - coacervates, already had the beginnings of feedback - the exchange of substances of their internal environment with the external one. Perhaps one of the defining moments in the emergence of life was the formation of a membrane with the rudiments of selective permeability and separating the system from the external environment.

In more detail, the effect of feedbacks can be considered on the example of the growth in the population of some species, for example, small fish, depending on the availability of food (plankton) and the presence of predatory fish. The more food, the more offspring of fish can feed and then give new offspring. With an unlimited amount of food and the absence of predators and diseases in fish, their numbers could increase indefinitely. Here there is a positive feedback, expressed in the fact that the process of growth of the fish population leads to an even greater (in geometric progression) its growth. In the case of the presence of predator fish, another inverse relationship arises: the number of predators will affect the amount of food for them (the number of small fish). This feedback will be negative. As a result of the action of feedbacks, the abundance in populations is undulating, and fluctuations in abundance will occur around a certain average level.

In highly organized animals, the activity of the central nervous system in the norm always includes as a necessary condition the presence of feedback. Thus, any action of an animal, such as chasing prey, is accompanied by impulses coming from the central nervous system to the muscles (running, grasping the prey), and feedback signals from the sense organs (vision, proprioceptors, etc.), which make it possible to take into account the results of efforts and correct them. in connection with the course of events.

Self-regulation of vital processes is also due to feedback. Yes, rise blood pressure above the norm is perceived by special receptors that signal this to the vasomotor centers of the nervous system. This results in centrifugal impulses leading to pressure reduction. Such a process is an example of the negative feedback most often observed in stable living systems. Most of the regulatory systems of animal and plant organisms work according to this principle. Positive feedback prevails during the period of embryonic development.

Many processes in ecology, such as the regulation of population dynamics, are also based on positive and negative O. s. So, a special case negative feedback is considered by the Italian mathematician V. Volterra the predator-prey system. An increase in the number of prey contributes to increased reproduction of predators, and an increase in the number of the latter, on the contrary, leads to a decrease in the number of prey. Although in this way the balance is maintained in nature, but due to the delay in the reproduction of animals, it takes the form of waves of life - wide fluctuations in the number of animals around the average level.

On molecular level according to the principle of O. s. a huge number of enzymatic reactions occurring simultaneously in a living cell is regulated. Coordination of this complex interconnected system is carried out by changing the activity of enzymes (negative feedback is carried out by inhibitors, positive - by stimulators) or the rate of their synthesis (feedback is carried out by effectors).

Combinations of positive and negative feedbacks cause an alternative change in physiological states (for example, sleep - wakefulness). The study of the development curve of pathological processes of a non-infectious nature (trophic ulcers, hypertension, manic-depressive psychosis, epilepsy, etc.) allows, based on the result, to determine the most likely type of feedback underlying the disease and limit the study of its etiology and pathogenesis mechanisms of a certain category. Living objects as the most perfect self-regulating systems are rich in various types of feedback; the study of the latter is very productive for the study of biological phenomena and the establishment of their specificity.

Thus, the general characteristics of feedbacks can be formulated as follows:

Negative feedbacks contribute to the restoration of the initial state. Positive - take the body further and further from the initial state.

Self-organization at all levels begins on the basis of positive feedback mechanisms, which are then subject to negative feedback restrictions.

Immunity(lat. immunitas- liberation, getting rid of something) - immunity, resistance of the body to infections and invasions of foreign organisms (including pathogens), as well as to the effects of foreign substances with antigenic properties. Immune reactions also occur to the body's own cells, which are antigenically altered.

Provides homeostasis of the body at the cellular and molecular level of organization. Implemented by the immune system.

The biological meaning of immunity is to ensure the genetic integrity of the organism throughout its individual life. The development of the immune system has led to the possibility of the existence of complexly organized multicellular organisms.

DNA in the composition of chromosomes can be stacked with different densities, depending on their functional activity and the stage of the cell cycle. In this regard, two states of chromosomes are distinguished - interphase and mitotic. Mitotic chromosomes are formed in a cell during mitosis. These are non-working chromosomes, and the DNA molecules in them are packed extremely tightly. Suffice it to say that the total length of the metaphase chromosomes is approximately 104 times less than the length of the entire DNA contained in the nucleus. Due to such compactness of mitotic chromosomes, a uniform distribution of genetic material between daughter cells during mitosis is ensured.

Ticket 33 special or giant chromosomes

Polytene chromosomes - giant interphase chromosomes that arise in some types of specialized cells as a result of two processes: firstly, multiple DNA replication, not accompanied by cell division, and secondly, lateral chromatid conjugation. Cells that have polythene chromosomes lose their ability to divide, they are differentiated and actively secrete, that is, polytenization of chromosomes is a way to increase the number of copies of genes for the synthesis of a product. The characteristic shape and size of polytene chromosomes are achieved due to their maximum despiralization and multiple reproduction of chromosomes without their subsequent divergence, that is, they are formed as a result of endomitosis. Polytene chromosomes have a characteristic transverse striation due to the presence of areas of denser spiralization of chromonemes - chromomeres. Dark areas (i.e., chromomeres) contain coiled inactive chromatin, while light bands indicate an area with increased transcriptional activity. A clear distinction between dark discs and light interdiscal areas is explained by non-disjunction of child chromonemes. For this reason, all the features of a separate chromonema, including the chromomeric pattern, become more pronounced. In fact, polytene chromosomes are a pair of giant homologous chromosomes in a state of perfectly precise somatic conjugation. In this case, the disks and interdisk regions of the homologues are located strictly parallel and closely spaced. Such conjugation is not characteristic of the vast majority of somatic cells.

In polytene chromosomes, the transcription process is accompanied by the formation of the so-called. puffs - characteristic swellings of certain disks, which are formed as a result of local decompactization of DNA in them. Large puffs are called Balbiani rings.

Puffing is characteristic of the larval stage. The formation and disappearance of puffs is regulated by the internal environment of the body in accordance with the stage of development.

Polytene chromosomes contain a large number of copies of genes, which greatly enhances gene expression. This, in turn, increases the production of essential proteins. For example, in the cells of the salivary glands of D. melanogaster larvae, chromosome polytenization is necessary for the formation of a large amount of sticky substance before pupation.

Ticket 35 ultrastructure of mitochondria, their function, origin.

Mitochondria, regardless of their size or shape, have a universal structure, their ultrastructure is uniform. Mitochondria are bounded by two membranes .

outer membrane The outer membrane of the mitochondrion has a thickness of about 7 nm, does not form invaginations and folds, and is closed on itself. The main function is to separate the mitochondria from the cytoplasm. The outer membrane of the mitochondria is composed of lipids interspersed with proteins. plays a special role porin- channel-forming protein: it forms holes in the outer membrane with a diameter of 2-3 nm, through which small molecules and ions weighing up to 5 kDa can penetrate. Large molecules can only cross the outer membrane through active transport across mitochondrial membrane transport proteins. The outer mitochondrial membrane can interact with the endoplasmic reticulum membrane; it plays an important role in the transport of lipids and calcium ions.

intermembrane space

The intermembrane space is the space between the outer and inner membranes of the mitochondria. Its thickness is 10-20 nm. Since the outer membrane of the mitochondria is permeable to small molecules and ions, their concentration in the periplasmic space differs little from that in the cytoplasm. On the contrary, for transport from the cytoplasm to the periplasmic space, large proteins need to have specific signal peptides; therefore, the protein components of the periplasmic space and cytoplasm are different. One of the proteins contained not only in the inner membrane, but also in the periplasmic space, is cytochrome c

Inner membrane

The inner membrane consists mainly of protein complexes and forms numerous ridge-like folds - cristae, characteristic feature composition of the inner membrane of mitochondria is the presence in it cardiolipin- a special phospholipid containing four fatty acids at once and making the membrane absolutely impermeable to protons. The outer and inner membranes touch in some places, there is a special receptor protein that facilitates the transport of mitochondrial proteins encoded in the nucleus into the mitochondrial matrix.

One of the main functions of mitochondria is the synthesis of ATP, the universal form of chemical energy in any living cell.

According to the theory symbiogenesis, mitochondria appeared as a result of the capture of primitive cells (prokaryotes) of bacteria. Cells that could not themselves use oxygen to generate energy had serious limitations in their ability to develop; bacteria (progenotes) could do it. In the process of developing such relationships, the progenotes transferred many of their genes to the nucleus that was formed, thanks to increased energy efficiency, now already eukaryotes.