In the microscopic analysis of chromosomes, first of all, their differences in shape and size are visible. The structure of each chromosome is purely individual. It can also be seen that chromosomes have common morphological features. They consist of two strands - chromatid, located in parallel and interconnected at one point, called centromere or primary stretch. On some chromosomes, one can see secondary stretch. It is a characteristic feature that allows you to identify individual chromosomes in a cell. If the secondary constriction is located close to the end of the chromosome, then the distal region bounded by it is called satellite. Chromosomes containing a satellite are referred to as AT chromosomes. On some of them, the formation of nucleoli occurs in the body phase.
The ends of chromosomes have a special structure and are called telomeres. Telomere regions have a certain polarity that prevents them from connecting to each other when broken or with the free ends of chromosomes. The section of chromatid (chromosome) from telomere to centromere is called arm of the chromosome. Each chromosome has two arms. Depending on the ratio of the lengths of the arms, three types of chromosomes are distinguished: 1) metacentric(equal-arms); 2) submetacentric(unequal shoulders); 3) acrocentric, in which one shoulder is very short and not always clearly distinguishable.
At the Paris Conference on the Standardization of Karyotypes, instead of the morphological terms "metacentrics" or "acrocentrics", in connection with the development of new methods for obtaining "striped" chromosomes, a symbolism was proposed in which all chromosomes of a set are assigned a rank (serial number) in descending order of magnitude and in both On the shoulders of each chromosome (p - short arm, q - long arm), sections of the arms and stripes in each section are numbered in the direction from the centromere. Such a notation allows a detailed description of chromosome anomalies.
Along with the location of the centromere, the presence of a secondary constriction and a satellite, their length is important for determining individual chromosomes. For each chromosome of a certain set, its length remains relatively constant. Measurement of chromosomes is necessary to study their variability in ontogeny in connection with diseases, anomalies, and impaired reproductive function.
Fine structure of chromosomes. Chemical analysis of the structure of chromosomes showed the presence of two main components in them: deoxyribonucleic acid(DNA) and protein type histones and protomite(in sex cells). Studies of the fine submolecular structure of chromosomes led scientists to the conclusion that each chromatid contains one strand - lameness. Each chromoneme consists of one DNA molecule. The structural basis of the chromatid is a strand of protein nature. The chromoneme is arranged in a chromatid in a shape close to a spiral. Evidence of this assumption was obtained, in particular, in the study of the smallest exchange particles of sister chromatids, which were located across the chromosome.
Nucleosomal (nucleosome strand): core of 8 molecules (except H1), DNA is wound around the core, a linker is between them. Less salt means less nucleosome. The density is 6-7 times greater.
Supernucleosomal (chromatin fibril): H1 brings the linker and 2 cores together. 40 times thicker. gene inactivation.
Chromatid (loop): the thread spirals, forms loops and bends. Thicker by 10-20 times.
Metaphase chromosome: supercompactization of chromatin.
Chromonema - the first level of compaction in which chromatin is visible.
Chromomere - area of chromonema.
Morphofunctional characteristics of chromosomes. Types and rules of chromosomes
The primary constriction is the kinetochore, or centromere, a region of the chromosome without DNA. Metacentric - equilateral, submetacentric - unequal, acrocentric - sharply unequal, telocentric - without a shoulder. Long - q, short - p. The secondary constriction separates the satellite and its filament from the chromosome.
Chromosome rules:
1) Number constancy
2) Pairings
3) Individualities (non-homologous are not similar)
Karyotype. Idiogram. Classification of chromosomes
Karyotype- diploid set of chromosomes.
Idiogram- number of chromosomes in descending order of size and shift of the centromeric index.
Denver classification:
A– 1-3 pairs, large sub/metacentric.
V- 4-5 pairs, large metacentric.
WITH- 6-12 + X, medium submetacentric.
D– 13-15 pairs, acrocentric.
E–16-18 pairs, relatively small sub/metacentric.
F–19-20 pairs, small submetacentric.
G–21-22 + Y, the smallest acrocentric.
Polytene chromosomes: reproduction of chromonemes (thin structures); all phases of mitosis fall out, except for the reduction of chromonemes; dark transverse stripes are formed; found in Diptera, ciliates, plants; used to build chromosome maps, detect rearrangements.
cell theory
Purkyne- the nucleus in the egg Brown- nucleus in a plant cell Schleiden- a conclusion about the role of the nucleus.
Shvannovskaya theory:
1) The cell is the structure of all organisms.
2) The formation of cells determines the growth, development and differentiation of tissues.
3) A cell is an individual, an organism is a sum.
4) New cells arise from the cytoblast.
Virchow- a cell from a cell.
Modern theory:
1) A cell is a structural unit of a living thing.
2) Cells of unicellular and multicellular are similar in structure and manifestations of vital activity
3) Reproduction by division.
4) Cells form tissues, and those form organs.
Additional: cells are totipotent - they can give rise to any cell. Pluri - any, except for extra-embryonic (placenta, yolk sac), uni - only one.
Breath. Fermentation
Breath:
Stages:
1) Preparatory: proteins = amino acids, fat = glycerol and fatty acids, sugars = glucose. There is little energy, it dissipates and even requires.
2) Incomplete: anoxic, glycolysis.
Glucose \u003d pyruvic acid \u003d 2 ATP + 2 OVER * H 2 or OVER * H + H +
10 cascade reactions. Energy is released by 2 ATP and dissipation.
3) Oxygen:
I. Oxidative decarboxylation:
PVC is destroyed = H 2 (–CO 2), activates enzymes.
II. Krebs cycle: NAD and FAD
III. ETC, H breaks down to e - and H + , p accumulate in the intermembrane space, form a proton reservoir, electrons accumulate energy, cross the membrane 3 times, enter the matrix, combine with oxygen, ionize it; the potential difference grows, the structure of ATP synthetase changes, the channel opens, the proton pump starts working, protons are pumped into the matrix, water is combined with oxygen ions, energy is 34 ATP.
During glycolysis, each glucose molecule is broken down into two molecules of pyruvic acid (PVA). In this case, energy is released, part of which is dissipated in the form of heat, and the rest is used for synthesis. 2 ATP molecules. Intermediate products of glycolysis undergo oxidation: hydrogen atoms are split off from them, which are used to restore NDD +.
NAD - nicotinamide adenine dinucleotide - a substance that performs the function of a carrier of hydrogen atoms in the cell. NAD that has attached two hydrogen atoms is called reduced (written as NAD "H + H +). Reduced NAD can donate hydrogen atoms to other substances and go into an oxidized form (NAD +).
Thus, the process of glycolysis can be expressed by the following summary equation (for simplicity, in all equations of energy metabolism reactions, water molecules formed during the synthesis of ATP are not indicated):
C 6 H 12 0 6 + 2NAD + + 2ADP + 2H 3 P0 4 \u003d 2C 3 H 4 0 3 + 2NADH + H + + 2ATP
As a result of glycolysis, only about 5% of the energy contained in the chemical bonds of glucose molecules is released. A significant part of the energy is contained in the product of glycolysis - PVC. Therefore, during aerobic respiration, after glycolysis, the final stage follows - oxygen, or aerobic.
Pyruvic acid, formed as a result of glycolysis, enters the mitochondrial matrix, where it is completely cleaved and oxidized to end products - CO 2 and H 2 O. The reduced NAD formed during glycolysis also enters the mitochondria, where it undergoes oxidation. During the aerobic stage of respiration, oxygen is consumed and 36 ATP molecules(calculated per 2 PVC molecules) CO 2 is released from mitochondria into the hyaloplasm of the cell, and then into the environment. So, the total equation of the oxygen stage of respiration can be represented as follows:
2C 3 H 4 0 3 + 60 2 + 2NADH + H+ + 36ADP + 36H 3 P0 4 = 6C0 2 + 6H 2 0 + + 2NAD+ + 36ATP
In the matrix of mitochondria, PVC undergoes complex enzymatic cleavage, the products of which are carbon dioxide and hydrogen atoms. The latter are delivered by NAD and FAD (flavin adenine dinucleotide) carriers to the inner mitochondrial membrane.
The inner membrane of mitochondria contains the enzyme ATP synthetase, as well as protein complexes that form the electron transport chain (ETC). As a result of the functioning of the ETC components, the hydrogen atoms obtained from NAD and FAD are separated into protons (H +) and electrons. Protons are transported across the inner mitochondrial membrane and accumulate in the intermembrane space. With the help of ETC, electrons are delivered to the matrix to the final acceptor - oxygen (О 2). As a result, O 2- anions are formed.
The accumulation of protons in the intermembrane space leads to the emergence of an electrochemical potential on the inner membrane of mitochondria. The energy released during the movement of electrons along the ETC is used to transport protons through the inner mitochondrial membrane into the intermembrane space. In this way, potential energy is accumulated, which is composed of the proton gradient and the electric potential. This energy is released as protons return back to the mitochondrial matrix along their electrochemical gradient. The return occurs through a special protein complex - ATP synthase; the process of moving protons along their electrochemical gradient is called chemiosmosis. ATP synthase uses the energy released during chemiosmosis to synthesize ATP from ADP during the phosphorylation reaction. This reaction is triggered by a flood of protons that cause a portion of the ATP synthase to rotate; thus, ATP synthase works like a spinning molecular motor.
Electrochemical energy is used to synthesize a large number of ATP molecules. In the matrix, protons combine with oxygen anions to form water.
Therefore, with the complete breakdown of one glucose molecule, the cell can synthesize 38 ATP molecules(2 molecules during glycolysis and 36 molecules during the oxygen stage). The general equation for aerobic respiration can be written as follows:
C 6 H 12 0 6 + 60 2 + 38ADP + 38H 3 P0 4 \u003d 6C0 2 + 6H 2 0 + 38ATP
Carbohydrates are the main source of energy for cells, but the breakdown products of fats and proteins can also be used in the processes of energy metabolism.
Fermentation:
Fermentation- a metabolic process in which ATP is regenerated, and the products of the breakdown of an organic substrate can serve simultaneously as donors and acceptors of hydrogen. Fermentation is the anaerobic (occurring without the participation of oxygen) metabolic breakdown of nutrient molecules, such as glucose.
Although the last step of fermentation (the conversion of pyruvate to fermentation end products) does not release energy, it is essential for the anaerobic cell because it regenerates nicotinamide adenine dinucleotide (NAD+), which is required for glycolysis. This is important for the normal functioning of the cell, since glycolysis for many organisms is the only source of ATP under anaerobic conditions.
During fermentation, partial oxidation of substrates occurs, in which hydrogen is transferred to NAD + . During other stages of fermentation, its intermediates serve as acceptors of hydrogen, which is part of NAD*H; during the regeneration of NAD + they are restored, and the products of restoration are removed from the cell.
The end products of fermentation contain chemical energy (they are not fully oxidized), but are considered waste because they cannot be further metabolized in the absence of oxygen (or other highly oxidized electron acceptors) and are often excreted from the cell. The production of ATP by fermentation is less efficient than by oxidative phosphorylation, when pyruvate is completely oxidized to carbon dioxide. During different types of fermentation, two to four ATP molecules are produced per molecule of glucose.
· Alcoholic fermentation (carried out by yeast and some types of bacteria), during which pyruvate is split into ethanol and carbon dioxide. One molecule of glucose results in two molecules of alcohol (ethanol) and two molecules of carbon dioxide. This type of fermentation is very important in the production of bread, brewing, winemaking and distillation. If the sourdough contains a high concentration of pectin, a small amount of methanol may also be produced. Usually only one of the products is used; in the production of bread, alcohol is volatilized during baking, and in the production of alcohol, carbon dioxide is usually released into the atmosphere, although in recent years efforts have been made to recycle it.
Alcohol + 2NAD + + 2ADP 2 to-you \u003d 2 mol. to-you + 2NAD * H + H + + 2ATP
PVC = acetaldehyde + CO 2
2 aldehydes + 2NAD*H+H + = 2 alcohols + 2NAD +
Lactic acid fermentation, during which pyruvate is reduced to lactic acid, is carried out by lactic acid bacteria and other organisms. When milk is fermented, lactic acid bacteria convert lactose into lactic acid, turning milk into fermented milk products (yogurt, curdled milk); lactic acid gives these products a sour taste.
Glucose + 2NAD + +2ADP + 2 PVC = 2 mol. to-you + 2NAD * H + H + + 2ATP
2 mol. to-you + 2NAD * H + H + \u003d 2 mol. to-you + 2ATP
Glucose + 2ADP + 2 to-you \u003d 2 mol. to-you + 2ATP
Lactic acid fermentation can also occur in animal muscles when the energy demand is greater than that provided by the already available ATP and the work of the Krebs cycle. When the lactate concentration reaches more than 2 mmol / l, the Krebs cycle begins to work more intensively and the Cori cycle resumes.
Burning sensations in the muscles during strenuous exercise are correlated with insufficient work of the Cori cycle and an increase in the concentration of lactic acid above 4 mmol / l, since oxygen is converted to carbon dioxide by aerobic glycolysis faster than the body replenishes the supply of oxygen; at the same time, it must be remembered that soreness in the muscles after exercise can be caused not only by a high level of lactic acid, but also by microtrauma of muscle fibers. The body shifts to this less efficient, but faster, method of producing ATP under conditions of increased stress, when the Krebs cycle cannot keep up with providing ATP to the muscles. The liver then gets rid of excess lactate, converting it through the Cori cycle into glucose for return to the muscles for reuse or conversion into liver glycogen and building up its own energy reserves.
Acetic acid fermentation is carried out by many bacteria. Vinegar (acetic acid) is a direct result of bacterial fermentation. When pickling foods, acetic acid protects food from disease-causing and rotting bacteria.
Glucose + 2NAD + + 2ADP + 2 k-you \u003d 2 PVC + 2NAD * H + H + + 2ATP
2 PVC = 2 aldehydes + 2CO 2
2 aldehydes + O 2 = 2 acetic acid
· Butyric fermentation leads to the formation of butyric acid; its causative agents are some anaerobic bacteria.
· Alkaline (methane) fermentation - a method of anaerobic respiration of certain groups of bacteria - is used to treat wastewater in the food and pulp and paper industries.
16) Coding of genetic information in a cell. Properties of the genetic code:
1) Tripletity. The mRNA triplet is a codon.
2) Degeneracy
3) Continuity
4) AUG - starting
5) Versatility
6) UAG - amber, UAA - ocher, UGA - opal. Terminators.
protein synthesis
Assimilation = anabolism = plastic metabolism. Dissimilation = catabolism = energy metabolism.
Components: DNA, restriction enzyme, polymerase, RNA nucleotides, t-RNA, r-RNA, ribosomes, amino acids, enzymatic complex, GTP, activated amino acid.
Activation:
1) the enzyme aminoacyl-t-RNA synthetase attaches an amino acid and ATP - activation - attachment of t-RNA - a bond is formed with t-RNA with a.k., AMP release - a complex in FCR - binding of aminoacyl-t-RNA to ribosomes, incorporation of an amino acid into a protein to release tRNA.
In prokaryotes, mRNA can be read by ribosomes into the amino acid sequence of proteins immediately after transcription, while in eukaryotes it is transported from the nucleus to the cytoplasm, where ribosomes are located. The process of protein synthesis based on an mRNA molecule is called translation. The ribosome contains 2 functional sites for interaction with tRNA: aminoacyl (acceptor) and peptidyl (donor). Aminoacyl-t-RNA enters the acceptor site of the ribosome and interacts to form hydrogen bonds between codon and anticodon triplets. After the formation of hydrogen bonds, the system advances 1 codon and ends up in the donor site. At the same time, a new codon appears in the vacated acceptor site, and the corresponding aminoacyl-t-RNA is attached to it. During the initial stage of protein biosynthesis, initiation, the methionine codon is usually recognized as a small subunit of the ribosome, to which the methionine t-RNA is attached with the help of proteins. After recognition of the start codon, the large subunit joins the small subunit and the second stage of translation begins - elongation. With each movement of the ribosome from the 5" to the 3" end of the mRNA, one codon is read through the formation of hydrogen bonds between the three nucleotides of the mRNA and its complementary anticodon of the tRNA to which the corresponding amino acid is attached. Synthesis of the peptide bond is catalyzed by r-RNA, which forms the peptidyl transferase center of the ribosome. rRNA catalyzes the formation of a peptide bond between the last amino acid of the growing peptide and the amino acid attached to the tRNA, positioning the nitrogen and carbon atoms in a position favorable for the reaction to proceed. The third and final stage of translation, termination, occurs when the ribosome reaches the stop codon, after which protein termination factors hydrolyze the last t-RNA from the protein, stopping its synthesis. Thus, in ribosomes, proteins are always synthesized from the N- to the C-terminus.
Transport
Diffusion: through the lipid layer - water, oxygen, carbon dioxide, urea, ethanol (hydrophobic faster than hydrophilic); through protein pores - ions, water (transmembrane - integral - proteins form pores); light - glucose, amino acids, nucleotides, glycerol (through carrier proteins);
Active transport: ions, amino acids in the intestines, calcium in the muscles, glucose in the kidneys. The carrier protein is activated by a phosphate group that is cleaved from ATP during hydrolysis, a bond is formed with the transferred substance (temporary).
Phagocytosis: capillary cells of the bone marrow, spleen, liver, adrenal glands, leukocytes.
Pinocytosis: leukocytes, liver cells, kidney cells, amoeba.
cell cycle
Interphase– 2n2C; rest period - neurons, lens cells; liver and leukocytes - optional.
Presynthetic period: the cell grows, performs its functions. The chromatids are despiralized. RNA, proteins, DNA nucleotides are synthesized, the number of ribosomes increases, ATP accumulates. The period lasts about 12 hours, but can take several months. The content of genetic material is 2n1chr2c.
Synthetic: replication of DNA molecules occurs - each chromatid completes its own similar. The content of the genetic material becomes 2n2chr4c. The centrioles double. Are synthesized
RNA, ATP and histone proteins. The cell continues to perform its functions. The duration of the period is up to 8 hours.
Postsynthetic: ATP energy is accumulated, RNA, nuclear proteins and tubulin proteins are actively synthesized, which are necessary for building the achromatin spindle of division. The content of the genetic
material does not change: 2n2chr4s. By the end of the period, all synthetic processes slow down, the viscosity of the cytoplasm changes.
Division. Amitosis
Division:
Binary, mitosis, amitosis, meiosis.
Amitosis:
Uniform, uneven, multiple, without cytotomy.
Generative- during the division of highly specialized cells (liver, epidermis) and the macronucleus of ciliates.
Degenerative- fragmentation and budding of nuclei.
Reactive– with damaging effects, without cytotomy, multinucleation.
Ligamentation of the nucleolus, nucleus and cytoplasm. The nucleus is divided into more than 2 parts - fragmentation, schizogony. The destruction of the karyolemma and the nucleolus does not occur. The cell does not lose functional activity.
Mitosis
Causes:
ü change in the nuclear-cytoplasmic ratio;
ü the appearance of "mitogenetic rays" - dividing cells "force" adjacent cells to enter into mitosis;
ü the presence of "wound hormones" - damaged cells secrete special substances that cause mitosis of intact cells.
Some specific mitogens (erythropoietin, fibroblast growth factors, estrogens) stimulate mitosis.
the amount of growth substrate.
ü Availability of free space for distribution.
secretion by surrounding cells of substances that affect growth and division.
ü positional information.
ü intercellular contacts.
In prophase: two-chromatid chromosomes in the hyaloplasm look like a ball, the centro divides, a radiant figure is formed, the spindle consists of tubes: polar (solid) and chromosome.
In prometaphase: protoplasm with slight viscosity in the center of the cell, chromosomes are directed to the equator of the cell, the karyolemma is dissolved.
In metaphase: the formation of the fission spindle is completed, maximum spiralization, chromosomes split longitudinally into chromatids.
In anaphase: discrepancy, the cytoplasm looks like a boiling liquid.
In telophase: cell center deactivated, annular constriction or median lamina.
Meaning:
- maintaining the constancy of the number of chromosomes, ensuring genetic continuity in cell populations;
- uniform distribution of chromosomes and genetic information between daughter cells;
Endomitosis: after replication, division does not occur. It occurs in actively functioning cells in nematodes, crustaceans, and in roots.
DNA is a right-handed double-stranded helix made up of nucleotides. Nucleotides, in turn, consist of a nitrogenous base - a carbohydrate-ost. phosphorus. to-you.
Nitrogenous bases:
1) Purine
Adenine(A)
Guanine(G)
2) pyrimidine
Cytosine(C)
Uracil(U)
Nitrogenous bases are able to form pairs according to the principle of complementarity
Nucleotides are united in a chain by simple covalent phosphorus diester bonds.
The structure of DNA.
Between strands of DNA-hydrogen bonds, which occur between nitrogenous bases according to the principle of complementarity.
Role in DNA cells.
1.stores, transfer of inherited information.
Chromosomes.
Chemical composition and structure of chromosomes.
They are mainly made up of DNA and proteins. Cats form a nucleoprotein complex-chromatin, which received its name for its ability to stain with basic dyes.
The amount of DNA in the nuclei of cells of an organism of a given species is constant and directly proportional to their ploidy. In diploid somatic organisms, it is twice as high as in gametes.
Forms of chromosomes.
Distinguish several. Chromosome shapes: equal-armed (with a centromere in the middle), not equal-armed (with a centromere shifted to one of the ends), rod-shaped (with a centromere practically located at the end of the chromosome) and dotted - very small, the shape of which is difficult to determine.
Methods of asexual and sexual reproduction
asexual reproduction- the beginning of a new organism is given by 1 parent, the descendants are exact genetic copies of the mothers. organism (the basis of cell division is mitosis). Wireless dim. contributes to the genetic stability of the species.
Types in multicellular:
Polyembryony– type of free reproduction in which the zygote divides into several blastomeres, each of which develops into a full-fledged independent organism (Ex: identical twins).
Vegetative multiplication- reproduction by body parts.
a) in plants, the methods are diverse - shoots, roots, leaves, etc.
b) in animals
Fragmentation - the disintegration of the body into fragments, each of which restores itself to a full-fledged organism (white planarian)
Dividing into 2 parts (earthworm)
Budding (hydra)
sporulation(ferns, horsetails, club mosses, higher spore plants)
For unicellular:
Division by 2: across (mitosis, ciliates), longitudinal (euglena green), without orientation (amoeba)
schizogony- multiple division of the nucleus, followed by grouping around each nucleus of the cytoplasm and the disintegration of the cell into many small cells (malarial plasmodium)
Sporogony(malarial plasmodium - multiple cell division with subsequent decay into many cells, however, division I is meiosis)
sporulation(chlamydomonas)
sexual reproduction- the beginning of a new organism is given 2 births. individuals, descendants - are genetically different from parents due to crossing over and independent. divergence of homologous chromosomes, as well as the phenomenon of random fertilization (based on division - meiosis). The genetic diversity of the offspring is increased→survival under changing conditions.
For unicellular:
Agametogony(no gamete formation) Ex: conjugation
gametogony(with the formation of gametes):
a) isogamy (male and female gametes are mobile, outwardly indistinguishable)
b) heterogamy (both gametes are mobile, but women are much larger)
oogamy(female large and fixed, male small and mobile) Ex: volvox
For multicellular organisms:
With fertilization
Without fertilization(parthenogenesis)
Gynogenesis (the beginning of a new organism gives an unfertilized egg). With the development of neopl. ovum bees develop drones.
Androgenesis (the nucleus of the egg dies, a spermatozoon (1-haploid, 2-diploid) penetrates into it, the egg carries the genetic material of the father)
There are obligate (permanent) and facultative (temporary) parthenogenesis.
Meiosis
This is an indirect cell division, in which 4 haploid daughter cells are formed from the mother, differing in genetic. material from meterin.
I division - reduction: the number of chromosomes is halved 2n4c→1n2c. On 4 phases:
Prophase I. On 5 stages:
1) leptotene - DNA spiralizes, chromosomes become visible in the form of thin threads, nuclei. The shell breaks up into fragments, the nucleolus disappears
2) zygotene - spiralization continues, chromosomes are more visible, origin. conjugation (the process of convergence of homologous xp-m → bivalents (tetrads) are formed))
3) pachytene - the formation of bivalents ends, origin. homologous exchange. uch-mi xp-m - crossing over.
4) diplotene - chr-we in bivalents diverge a little, remaining fastened in places of crossing over, chiasmata become visible
5) diakinesis - the chr-we in bivalents are separated from each other, the centrioles expand to different poles, spindle fibers are formed.
Metaphase I. Bivalents line up in the region. equator, spindle fibers are attached to the centromeres
Anaphase I. The division of the centromere does not occur. To the poles, there are whole homologous chr-s, each of which consists of 2 chromatids (1 chr-ma goes to one pole, the other to the other) There is law of independent discrepancy homol. xr-m: in each pair of xp-we diverge independently of each other.
Telophase I. At the poles, the DNA in the chromosomes is despiralized, the chromosomes are not visible, a nuclear envelope is formed around them, a nucleolus is formed, then cytokinesis occurs - the cytoplasm separates and 2 cells are formed (but in each cell 1n2c)
II division - equational: number of chromosomes = number of DNA 1n2c→1n1c
Prophase II, Metaphase II, Anaphase II, Telophase II - as in mitosis.
Meiosis Meaning:
1) underlies sexual reproduction, ensures the haploidy of gametes
2) helps to increase the genetic diversity of offspring→survival in changing conditions. environment.
Human genetics is a special section of genetics that studies the features of inheritance of traits in humans, hereditary diseases (medical genetics), and the genetic structure of human populations. Human genetics is the theoretical basis of modern medicine and modern health care. Human genetics studies the features of inheritance of traits in humans, hereditary diseases (medical genetics), and the genetic structure of human populations. Human genetics is the theoretical basis of modern medicine and modern healthcare
The tasks of medical genetics are to timely identify carriers of these diseases among parents, identify sick children and develop recommendations for their treatment.).
There are special sections of applied human genetics (environmental genetics, pharmacogenetics, genetic toxicology) that study the genetic foundations of health care. When developing drugs, when studying the body's response to adverse factors, it is necessary to take into account both the individual characteristics of people and the characteristics of human populations.
The cytological method is based on the microscopic examination of chromosomes in human cells. The cytogenetic method has been widely used since 1956, when J. Tio and L. Levan found that there are 46 chromosomes in the human karyotype.
The cytogenetic method is based on chromosome data. In 1960, at a scientific conference in Denver, a classification of identifiable chromosomes was adopted, according to which they were given numbers that increase as the size of the chromosomes decreases. This classification was refined at a conference in London (1963) and Chicago (1966).
The use of the cytogenetic method makes it possible to study the normal morphology of chromosomes and the karyotype as a whole, to determine the genetic sex of the organism, and, most importantly, to diagnose various chromosomal diseases associated with a change in the number of chromosomes or with a violation of the structure of chromosomes. The cytogenetic method makes it possible to study the processes of mutagenesis at the level of chromosomes and karyotype. The method is widely used in medical genetic counseling for the purposes of prenatal diagnosis of chromosomal diseases.
Cytological analysis includes three main stages:
cell culture;
The color of the drug;
Microscopic analysis of the drug.
Cytogenetic methods are also used to describe interphase cells. For example, by the presence or absence of sex chromatin (Barr bodies, which are inactivated X chromosomes) can not only determine the sex of individuals, but also identify some genetic diseases associated with a change in the number of X chromosomes.
Morphofunctional characteristics and classification of chromosomes. Human karyotype. cytological method.
Chromosomes (HYPERLINK "http://ru.wikipedia.org/wiki/%D0%94%D1%80%D0%B5%D0%B2%D0%BD%D0%B5%D0%B3%D1%80%D0 %B5%D1%87%D0%B5%D1%81%D0%BA%D0%B8%D0%B9_%D1%8F%D0%B7%D1%8B%D0%BA" \o "Ancient Greek" etc .-Greek χρῶμα - color and σῶμα - body) - nucleoprotein structures in the nucleus of a eukaryotic cell, which become easily visible in certain phases of the cell cycle (during mitosis or meiosis). Chromosomes are a high degree of condensation of chromatin, constantly present in the cell nucleus. Chromosomes contain most of the genetic information. The identification of chromosomes is based on the following features: the total length of the chromosome, the location of the centromere, the secondary constriction, etc.
Types of chromosome structure
There are four types of chromosome structure:
telocentric (rod-shaped chromosomes with a centromere located at the proximal end);
acrocentric (rod-shaped chromosomes with a very short, almost imperceptible second arm);
submetacentric (with shoulders of unequal length, resembling the letter L in shape);
metacentric (V-shaped chromosomes with arms of equal length).
The chromosome type is constant for each homologous chromosome and may be constant in all representatives of the same species or genus.
giant chromosomes
Such chromosomes, which are characterized by huge sizes, can be observed in some cells at certain stages of the cell cycle. For example, they are found in the cells of some tissues of dipteran insect larvae (polytene chromosomes) and in the oocytes of various vertebrates and invertebrates (lampbrush chromosomes). It was on preparations of giant chromosomes that it was possible to identify signs of gene activity.
Polytene chromosomes
The Balbiani were first discovered in 1881, but their cytogenetic role was identified by Kostov, Painter, Geitz and Bauer. Contained in the cells of the salivary glands, intestines, trachea, fat body and Malpighian vessels of Diptera larvae.
Bacterial chromosomes
Prokaryotes (archaea and bacteria, including mitochondria and plastids, permanently living in the cells of most eukaryotes) do not have chromosomes in the proper sense of the word. Most of them have only one DNA macromolecule in the cell, closed in a ring (this structure is called the nucleoid). Linear (not closed in a ring) DNA macromolecules were found in a number of bacteria. In addition to the nucleoid or linear macromolecules, DNA can be present in the cytoplasm of prokaryotic cells in the form of small DNA molecules closed in a ring, the so-called plasmids, which usually contain a small number of genes compared to the bacterial chromosome. The composition of plasmids can be variable, bacteria can exchange plasmids during the parasexual process.
Human karyotype (from Greek - nut, nucleus and - imprint, type) - a diploid human chromosome set, which is a set of morphologically distinct chromosomes introduced by parents during fertilization.
The chromosomes of a set are genetically unequal: each chromosome contains a group of different genes. All chromosomes in the human karyotype are divided into autosomes and sex chromosomes. There are 44 autosomes in the human karyotype (double set) - 22 pairs of homologous chromosomes and one pair of sex chromosomes - XX in women and XY in men.
Cytological research methods in medicine, cytological diagnostics, methods for recognizing diseases and studying the physiological state of the human body based on the study of cell morphology and cytochemical reactions. Are applied: 1) in oncology for the recognition of malignant and benign tumors; during mass preventive examinations in order to identify the early stages of the tumor process and precancerous diseases; when monitoring the course of anticancer treatment; 2) in hematology for diagnosing diseases and evaluating the effectiveness of their treatment; 3) in gynecology - both for the purpose of diagnosing oncological diseases, and for determining pregnancy, hormonal disorders, etc.; 4) for the recognition of many diseases of the respiratory, digestive, urinary, nervous system, etc. and evaluation of the results of their treatment.
Criteria for cytological diagnosis of diseases of the blood, reticuloendothelial system, certain diseases of the stomach, kidneys, pulmonary tuberculosis, skin diseases, etc. have been developed. If necessary, urgent cytological diagnostics is carried out. Cytological research methods are often combined with histological research.
88. Fertilization and ooplasmic segregation.
Fertilization
syngamy, in plants, animals and humans - the fusion of male and female germ cells - gametes, as a result of which a zygote is formed, capable of developing into a new organism. O. underlies sexual reproduction and ensures the transmission of hereditary traits from parents to descendants. Fertilization in plants. O. is characteristic of most plants; it is usually preceded by the formation of gametangia - the reproductive organs in which gametes develop. Often these processes are combined under the general name of the sexual process. Plants that have a sexual process also have meiosis in their development cycle, i.e., they exhibit a change in nuclear phases. Bacteria and blue-green algae do not have a typical sexual process; it is also unknown in some fungi. The types of the sexual process in lower plants are varied. Unicellular algae (for example, some chlamydomonas) turn into gametangia themselves, as it were, forming gametes; Conjugate algae (for example, spirogyra) are characterized by conjugation: the protoplast of one cell flows into another (belonging to the same or another individual), merging with its protoplast. The fusion of gametes with flagella of different sizes (larger - female, smaller - male; for example, in some chlamydomonas) is called heterogamy (See Heterogamy) (Fig. 1, 3). The fusion of a large flagellate-free female gamete (ovum) and a small male gamete, more often with flagella (sperm), less often without flagella (spermation), is called oogamy (See Oogamy). The female gametangia of most oogamous lower plants are called oogonia, while the male gametangia are called antheridia.
In seed plants that have sperm, the latter move to the eggs through the pollen tubes. In angiosperms, double fertilization occurs: one sperm fuses with the egg, the second with the central cell of the embryo sac (female outgrowth). The implementation of O., regardless of the presence of free water, is one of the most important adaptations of seed plants to existence on land.
Fertilization in animals and humans consists in the fusion (syngamy) of two gametes of different sexes - sperm and eggs. O. has a double meaning: 1) the contact of the sperm with the egg brings the latter out of its inhibited state and stimulates development; 2) the fusion of the haploid sperm and egg nuclei - karyogamy - leads to the emergence of a diploid synkaryon that combines paternal and maternal hereditary factors. The emergence of new combinations of these factors in O. creates genetic diversity that serves as material for natural selection and evolution of the species. A necessary prerequisite for O. is a halving of the number of chromosomes, which occurs during meiosis. The meeting of the spermatozoon with the egg is usually ensured by the swimming movements of male gametes after they are swept into the water or introduced into the female genital tract (see Insemination). The meeting of gametes is facilitated by the production of gamons by eggs (See Gamons), which enhance the movement of sperm and prolong the period of their motility, as well as substances that cause accumulation of sperm near the egg. A mature egg is surrounded by shells, which in some animals have openings for the penetration of spermatozoa - the Micropyle. In most animals, the micropyle is absent, and in order to reach the surface of the ooplasm, sperm must penetrate the membrane, which is carried out using a special sperm organelle - the acrosome. After the end of the sperm head touches the egg membrane, an acrosomal reaction occurs: the acrosome opens, releasing the contents of the acrosomal granule, and the enzymes contained in the granule dissolve the egg membranes. In the place where the acrosome has opened, its membrane merges with the plasma membrane of the sperm; at the base of the acrosome, the acrosomal membrane bends and forms one or more outgrowths, which are filled with (subacrosomal) material located between the acrosome and the nucleus, elongate and turn into acrosomal filaments or tubules. The acrosomal filament passes through the dissolved zone of the egg membrane, comes into contact with the plasma membrane of the egg and fuses with it.
Segregation is ooplasmic (biological), the occurrence of local differences in the properties of the ooplasm, which occurs during periods of growth and maturation of the oocyte, as well as in a fertilized egg. C. is the basis for the subsequent differentiation of the embryo: in the process of crushing the egg, sections of the ooplasm that differ in their properties fall into different blastomeres; interaction with them of cleavage nuclei identical in their potency leads to differential activation of the genome. In different animals, S. occurs at different times and is expressed to varying degrees. It is most pronounced in animals with a mosaic type of development, but it is also observed in animals with a regulatory type of development. Examples of S.: the formation of polar plasmas in mollusks, the concentration of RNA in the future dorsal hemisphere of the egg of mammals.
The set of chromosomes of a somatic cell that characterizes an organism of a given species is called karyotype (Fig. 2.12).
Rice. 2.12. Karyotype ( a) and idiogram ( b) human chromosomes
Chromosomes are divided into autosomes(the same for both sexes) and heterochromosomes, or sex chromosomes(different set for males and females). For example, a human karyotype contains 22 pairs of autosomes and two sex chromosomes - XX in a woman and XY y men (44+ XX and 44+ XY respectively). The somatic cells of organisms contain diploid (double) set of chromosomes, and gametes - haploid (single).
Idiogram- this is a systematized karyotype, in koto-1M chromosomes are arranged as their size decreases. It is not always possible to accurately arrange chromosomes in size, since some pairs of chromosomes have similar sizes. Therefore, in 1960 it was proposed Denver classification of chromosomes, which, in addition to size, takes into account the shape of the chromosomes, the position of the centromere, and the presence of secondary constrictions and satellites (Fig. 2.13). According to this classification, 23 pairs of human chromosomes were divided into 7 groups - from A to G. An important feature that facilitates classification is centromere index(CI), which reflects the ratio (in percent) of the length of the short arm to the length of the entire chromosome.
Rice. 2.13. Denver classification of human chromosomes
Consider groups of chromosomes.
Group A (chromosomes 1-3). These are large, metacentric and submetacentric chromosomes, their centromeric index is from 38 to 49. The first pair of chromosomes is the largest metacentric (CI 48-49), in the proximal part of the long arm near the centromere there may be a secondary constriction. The second pair of chromosomes is the largest submetacentric (CI 38-40). The third pair of chromosomes is 20% shorter than the first, the chromosomes are submetacentric (CI 45-46), easily identified.
Group B (chromosomes 4 and 5). These are large submetacentric chromosomes, their centromeric index is 24-30. They do not differ from each other with normal staining. The distribution of R- and G-segments (see below) is different for them.
Group C (chromosomes 6-12). Chromosomes of average size j measure, submetacentric, their centromeric index 27-35. In the 9th chromosome, a secondary constriction is often found. This group also includes the X chromosome. All chromosomes of this group can be identified using Q- and G-staining.
Group D (chromosomes 13-15). Chromosomes are acrocentric, very different from all other human chromosomes, their centromeric index is about 15. All three pairs have satellites. The long arms of these chromosomes differ in Q- and G-segments.
Group E (chromosomes 16-18). The chromosomes are relatively short, metacentric or submetacentric, their centromeric index is from 26 to 40 (chromosome 16 has a CI of about 40, chromosome 17 has a CI of 34, chromosome 18 has a CI of 26). In the long arm of the 16th chromosome, a secondary constriction is detected in 10% of cases.
Group F (chromosomes 19 and 20). Chromosomes are short, submetacentric, their centromeric index is 36-46. With normal staining, they look the same, but with differential staining, they are clearly distinguishable.
Group G (chromosomes 21 and 22). Chromosomes are small, acrocentric, their centromeric index is 13-33. This group also includes the Y chromosome. They are easily distinguishable by differential staining.
At the core Parisian classification of human chromosomes (1971) are methods of their special differential staining, in which each chromosome reveals a characteristic order of alternation of transverse light and dark segments, characteristic only for it (Fig. 2.14).
Rice. 2.14. Parisian classification of human chromosomes
Different types of segments are designated by the methods by which they are identified most clearly. For example, Q-segments are sections of chromosomes that fluoresce after staining with quinacrine mustard; segments are identified by Giemsa staining (Q- and G-segments are identical); R-segments are stained after controlled heat denaturation, etc. These methods make it possible to clearly differentiate human chromosomes within groups.
The short arm of chromosomes is denoted by the Latin letter p and the long q. Each chromosome arm is divided into regions numbered from centromere to telomere. In some short arms, one such region is distinguished, and in others (long) - up to four. The bands within the regions are numbered in order from the centromere. If the localization of the gene is precisely known, the band index is used to designate it. For example, the localization of the gene encoding esterase D is denoted 13 p 14, i.e., the fourth band of the first region of the short arm of the thirteenth chromosome. The localization of genes is not always known up to the band. Thus, the location of the retinoblastoma gene is indicated by 13 q, which means its localization in the long arm of the thirteenth chromosome.
The main functions of chromosomes are the storage, reproduction and transmission of genetic information during the reproduction of cells and organisms.
