What cell structures are DNA molecules localized in? Features of the circular DNA molecule of a prokaryotic cell

The structure and functioning of plant and animal cells have much in common.

Common features of plant and animal cells:

1. Fundamental unity of structure.

2. Similarities in the occurrence of many chemical processes in the cytoplasm and nucleus.

3. The unity of the principle of transmission of hereditary information during cell division.

4. Similar membrane structure.

Unity of chemical composition.

animal cell

plant cell

A plant cell differs from an animal cell in the following structural features:

1) A plant cell has a cell wall (wall).

The cell wall is located outside the plasma membrane (cytoplasmic membrane) and is formed due to the activity of cell organelles: the endoplasmic reticulum and the Golgi apparatus.

The basis of the cell wall is cellulose (fiber). Cells surrounded by a hard shell can absorb the substances they need from the environment only in a dissolved state.

Therefore, plants feed osmotically. The intensity of nutrition depends on the size of the plant body surface in contact with the environment. Therefore, the body of plants is more dissected than that of animals.

The existence of hard cell membranes in plants determines another feature of plant organisms - their immobility, while in animals there are few forms that lead an attached lifestyle.

2) Plants have special organelles in their cells - plastids.

The presence of plastids is associated with the peculiarities of plant metabolism and their autotrophic type of nutrition.

There are three types of plastids: leucoplasts - colorless plastids in which starch is synthesized from monosaccharides and disaccharides (there are leucoplasts that store proteins or fats);

chloroplasts - green plastids containing the pigment chlorophyll, where photosynthesis occurs;

chromoplasts that accumulate pigments from the group of carotenoids, which give them a color from yellow to red.

3) In a plant cell there are vacuoles bounded by a membrane - the tonoplast. Plants have a poorly developed waste excretion system, so substances that the cell does not need accumulate in vacuoles.

In addition, a number of accumulated substances determine the osmotic properties of the cell.

4) There are no centrioles (cell center) in a plant cell.

Similarities indicate the proximity of their origin.

Signs of difference indicate that the cells, together with their owners, have gone through a long path of historical development.

Prokaryotes and eukaryotes

All organisms with a cellular structure are divided into two groups: prenuclear (prokaryotes) and nuclear (eukaryotes).

The cells of prokaryotes, which include bacteria, unlike eukaryotes, have a relatively simple structure.

A prokaryotic cell does not have an organized nucleus; it contains only one chromosome, which is not separated from the rest of the cell by a membrane, but lies directly in the cytoplasm. However, it also records all the hereditary information of the bacterial cell.

The cytoplasm of prokaryotes, compared to the cytoplasm of eukaryotic cells, is much poorer in structural composition. There are numerous smaller ribosomes than in eukaryotic cells.

The functional role of mitochondria and chloroplasts in prokaryotic cells is performed by special, rather simply organized membrane folds.

Prokaryotic cells, like eukaryotic cells, are covered with a plasma membrane, on top of which is a cell membrane or mucous capsule.

Despite their relative simplicity, prokaryotes are typical independent cells.

Structure of a eukaryotic cell

Cell - the smallest unit of living things that underlies the structure and development of plant and animal organisms on our planet.

It is an elementary living system capable of self-renewal, self-regulation, and self-reproduction.

Although a single cell is the simplest form of life, its structure is quite complex. Advances in cytology have made it possible to penetrate into the deep mechanisms of cell structure and function. A powerful means of studying it is the electron microscope, which provides magnification up to 1,000,000 times and allows viewing objects at 200 nm.

Recall that using a light microscope you can study structures only about 0.4 microns in size. If we compare the resolving abilities of microscopes and the human eye, then the light microscope is 500 times stronger than the eye, and the electron microscope is 500 times stronger than the light microscope.

Rice. 1. Animal cell under an electron microscope

In addition to the electron microscope, cytology uses a number of biochemical and biophysical research methods to help study the composition and vital activity of the cell.

A living cell is delimited from its environment by an outer plasma membrane, consisting of three (protein-lipid) layers. The cell itself contains the nucleus and cytoplasm. The nucleus is also delimited from the cytoplasm by a three-layer plasma membrane (Fig. 1).

Cytoplasm. Cytoplasm is a semi-liquid mucous colorless mass containing 75-85% water, 10-12% proteins and amino acids, 4-6% carbohydrates, 2-3% fats and lipids, 1% inorganic and other substances.

The cytoplasmic contents of the cell are capable of movement, which contributes to the optimal placement of organelles, better biochemical reactions, release of metabolic products, etc. The cytoplasmic layer forms various formations: cilia, flagella, surface outgrowths.

The latter play an important role in the movement and connection of cells with each other in tissue.

The cytoplasm is penetrated by a complex mesh system connected to the outer plasma membrane and consisting of interconnected tubules, vesicles, and flattened sacs. This network structure is called vacuolar system. The main components of the vacuolar system are endoplasmic reticulum, Golgi complex, nuclear membrane.

Endoplasmic reticulum (ER). The name of this organelle reflects its location in the central part of the cytoplasm (Greek.

endon- inside). The EPS is a very branched interconnected system of tubules, tubes, vesicles, cisterns of various sizes and shapes, delimited by membranes from the cytoplasm of the cell. It comes in two types:

granular, consisting of tubules and cisterns, the surface of which is strewn with grains (granules), and agranular, i.e. smooth(without grains). Grana in the endoplasmic reticulum are nothing more than ribosomes.

It is interesting that in the cells of animal embryos, mainly granular EPS is observed, while in adult forms it is agranular. Knowing that ribosomes in the cytoplasm serve as the site of protein synthesis, it can be assumed that the granular network predominates in cells that actively synthesize protein. It is believed that the agranular network is more represented in those cells where active synthesis of lipids (fats and fat-like substances) occurs.

Both types of endoplasmic reticulum not only participate in the synthesis of organic substances, but also accumulate and transport them to their destinations, regulate the metabolism between the cell and its environment.

Ribosomes. Ribosomes are non-membrane cellular organelles consisting of ribonucleic acid and protein.

Their internal structure largely remains a mystery. In an electron microscope they look like round or mushroom-shaped granules. Each ribosome is divided by a groove into larger and smaller parts (subunits). Often several ribosomes are held together by a strand of special ribonucleic acid (RNA) called informational(i-RNA). Ribosomes perform the unique function of synthesizing protein molecules from amino acids.

Golgi complex. Biosynthesis products enter the lumens of the cavities and tubules of the ER, where they are concentrated and transported to a special apparatus - the Golgi complex, located near the nucleus.

The Golgi complex is involved in the transport of biosynthetic products to the cell surface and in their removal from the cell, in the formation of lysosomes, etc.

Lysosomes.Lysosomes(from Greek lyseo - I dissolve and soma - body). These are oval-shaped cell organelles surrounded by a single-layer membrane. They contain a set of enzymes that destroy proteins, carbohydrates, and lipids. If the lysosomal membrane is damaged, enzymes begin to break down and destroy the internal contents of the cell, and it dies.

Cellular center.Cell center can be observed in cells capable of dividing. It consists of two rod-shaped bodies - centrioles. Located near the nucleus and Golgi apparatus, the cell center participates in the process of cell division, in the formation fission spindles.

Energy organelles.Mitochondria(Greek - mitos - a thread, chondrion - granule) called the energy stations of cells.

This name is due to the fact that it is in the mitochondria that the energy contained in nutrients is extracted. The shape of mitochondria varies, but most often they have the appearance of threads or granules. Their size and number are also variable and depend on the functional activity of the cell.

Electron micrographs show that mitochondria consist of two membranes: outer and inner.

The inner membrane forms projections called Christami, which are completely covered with enzymes. The presence of cristae increases the total surface area of mitochondria, which is important for the active activity of enzymes. Enzymatic reactions occur on the cristae, as a result of which the energy-rich (macroergic) substance ATP (adenosine triphosphate) is synthesized from phosphate and ADP (adenosine diphosphate). The latter serves as the main source of energy for all intracellular processes.

Mitochondria contain their own specific DNA and ribosomes.

In this regard, they reproduce independently during cell division.

Chloroplasts - shaped like a disk or ball with a double shell - outer and inner. Inside the chloroplast there are also DNA, ribosomes and special membrane structures - grains, connected to each other and the inner membrane of the chloroplast. Gran membranes are located chlorophyll. Thanks to chlorophyll, chloroplasts convert the energy of sunlight into the chemical energy of ATP.

ATP energy is used in chloroplasts to synthesize carbohydrates from carbon dioxide and water.

Core.Core - the most prominent and largest organelle of the cell, which first attracted the attention of researchers. The nucleus is separated from the cytoplasm by a double membrane, which is directly connected to the ER and the Golgi complex. On nuclear membrane discovered pores, through which (as well as through the outer cytoplasmic membrane) some substances pass more easily than others, i.e.

e. pores provide selective permeability of the membrane.

The internal contents of the kernel are nuclear juice, filling the space between the structures of the nucleus. The core always contains one or more nucleoli. Ribosomes are formed in the nucleolus.

Therefore, there is a direct connection between cell activity and the size of the nucleoli: the more active the processes of protein biosynthesis occur, the larger the nucleoli, and vice versa, in cells where protein synthesis is limited, the nucleoli are either very small or completely absent.

The nucleus also contains DNA molecules connected to specific proteins - histones. During the process of cell division - mitosis - these nucleoproteins spiral and form dense formations - chromosomes, clearly visible in a light microscope.

The DNA of chromosomes contains hereditary information about all the characteristics and properties of a given cell, about the processes that should occur in it (for example, protein synthesis). In addition, mRNA is synthesized in the nucleus, which, after transportation to the cytoplasm, plays a significant role in transmitting information for the synthesis of protein molecules.

Source of assignments: https://ege.sdamgia.ru/ (decided by yourself)

Exercise 1.

Consider the diagram. Write down the missing term in your answer, indicated by a question mark in the diagram.

Explanation: The hypothalamus sends a signal to the pituitary gland (in fact, the hypothalamic-pituitary complex produces hormones), which secretes growth hormone.

The correct answer is the pituitary gland.

Task 2.

What sciences study living systems at the organismal level? Choose two correct answers out of five and write down the numbers under which they are indicated.

1. Anatomy

2. Biocenology

3. Physiology

4. Molecular biology

5. Evolutionary doctrine

Explanation: at the organismal level, living systems are studied by anatomy (organism structure) and physiology (internal processes).

The correct answer is 13.

Task 3.

In DNA, the share of nucleotides with adenine accounts for 18%. Determine the percentage of nucleotides containing cytosine that make up the molecules. Write down only the corresponding number in your answer.

Explanation: the share of nucleotides with adenine accounts for 18%. According to the principle of complementarity, adenine is associated with thymine, and cytosine is associated with guanine. This means that the number of nucleotides with thymine is also 18%. Then the share of nucleotides with cytosine and guanine accounts for 100% - (18% + 18%) = 64%.

Divide by 2, we get 32%.

The correct answer is 32%.

Task 4.

Choose two correct answers out of five. In what structures of eukaryotic cells are DNA molecules localized?

1. Cytoplasm

2. Core

3. Mitochondria

4. Ribosomes

5. Lysosomes

Explanation: DNA in eukaryotic cells is contained in the nucleus as a linear molecule (one or more) and in mitochondria (circular mitochondrial DNA), since previously mitochondria were free-living microorganisms and built like eukaryotic cells.

The correct answer is 23.

Task 5.

Establish a correspondence between the characteristics of a cell organelle and the organelle for which these characteristics are characteristic.

Signs of an organoid

A. Contains green pigment

B. Consists of a double membrane, thylakoids and grana

B. Converts light energy into chemical energy

D. Consists of a double membrane and cristae

D. Provides final oxidation of nutrients

E. Stores energy in the form of 38 moles of ATP when 1 mole of glucose is broken down

Organoids

1. Chloroplast

2. Mitochondria

Explanation:

chloroplasts are green plastids consisting of a double membrane, thylakoids and grana; they convert light energy into the energy of chemical bonds.

Mitochondria are double-membrane organelles with cristae (concavities of the inner membrane). Nutrient oxidation occurs in mitochondria, during which 38 ATP molecules are released per one glucose molecule.

The correct answer is 111222.

Task 7.

This list shows cells in which the set of chromosomes is haploid. Identify two characteristics that “drop out” from the general list, and write down the numbers under which they are indicated in your answer.

1. Fern prothallus cells

2. Moss boll cells

3. Rye sperm

4. Wheat endosperm cells

5. Horsetail Spores

Explanation: The haploid set of chromosomes is contained in the cells of the fern germ (as it develops from a haploid spore), in the sperm of rye (in the germ cells there is a haploid set of chromosomes) and horsetail spores (formed by meiosis). Moss boll cells and wheat endosperm cells have a diploid set of chromosomes.

The correct answer is 24.

Task 8.

Establish a correspondence between the method of reproduction and a specific example.

Example

A. Fern sporulation

B. Formation of chlamydomonas gametes

B. Formation of spores in sphagnum

D. Yeast budding

D. Fish spawning

Reproduction method

1. Asexual

2. Sexual

Explanation: asexual reproduction occurs without the participation of germ cells; this includes the sporulation of ferns and sphagnum moss, and the budding of yeast.

Sexual reproduction occurs with the participation of germ cells, that is, the formation of Chlamydomonas gametes and the spawning of fish.

The correct answer is 12112.

Task 9.

What features do mushrooms have? Choose three correct signs out of six.

1. Autotrophic organisms

2. Cell walls contain chitin

3. All multicellular

4. Some form mycorrhizae with plants

6. Grow throughout your life

Explanation: mushrooms are a separate kingdom of living organisms. Their cell walls contain chitin, some of them form mycorrhizae with plants and grow throughout their lives.

The correct answer is 246.

Task 10.

Establish a correspondence between the characteristics of an organism and the organism to which this characteristic belongs.

Signs

A. Store carbohydrates in the form of starch

B. The body is formed by hyphae

B. The cell wall contains chitin

D. During reproduction they form spores

E. Storage substance - glycogen

Organisms

1. Algae

2. Mushrooms

Explanation: algae are lower plants; in their cells carbohydrates are stored in the form of starch, contain a green pigment - chlorophyll and form zoospores during reproduction.

Mushrooms have a body formed by hyphae, their cell walls include chitin, and the storage substance of the cells is glycogen.

The correct answer is 122112.

Task 11.

Arrange the bones of the bird's hind limbs in the correct order, starting with the spine. Write down the corresponding sequence of numbers in your answer.

1. Shank

2. Shin bone

3. Fingers

4. Femur

Explanation: Let's look at the picture.

From top to bottom the bones are located: femur - tibia - tarsus - phalanges of the fingers.

The correct answer is 4213.

Task 12.

Select the signs of human unconditioned reflexes.

1. Not inherited

2. Produced during the process of evolution

3. Characteristic of all individuals of the species

4. Acquired during life

5. Passed on by inheritance

6. Individual

Explanation: unconditioned reflexes are those reflexes with which a certain type of living organism is born. They are produced in the process of evolution, are always characteristic of all individuals and are inherited.

The correct answer is 235.

Task 13.

Establish a correspondence between a person’s vital signs and disease diagnoses.

Vital signs

A. Vitamin deficiency C

B. Tooth loss

B. Increased levels of thyroxine in the blood

D. Increased blood glucose levels

D. Bulging eyes, goiter

E. Lack of insulin in the blood

Diagnosis

1. Diabetes mellitus

2. Scurvy

3. Graves' disease

Explanation: Diabetes mellitus comes in several types and is produced when insulin levels are low (insulin is a pancreatic hormone that transports glucose into cells); without insulin (or when there is a lack of it), glucose accumulates in the blood and ATP is not produced.

Scurvy is a disease of sailors due to a lack of vitamin C (vitaminosis C), characterized by tooth loss and bleeding gums.

Graves' disease develops when there is an increased level of thyroxine in the blood (hyperfunction of the thyroid gland), characterized by bulging eyes and goiter).

The correct answer is 223131.

Task 14.

Arrange the bones of the upper limb in the correct order, starting with the shoulder girdle. Write down the corresponding sequence of numbers in your answer.

1. Metacarpal bones

2. Humerus

3. Fingers

4. Radius

5. Carpal bones

Explanation: the skeleton of the free upper limb looks like this:

That is: humerus, radius, wrist bones, metacarpal bones, phalanges of the fingers.

The correct answer is 24513.

Task 15.

Select the characteristics that characterize natural selection as the driving force of evolution.

1. Source of evolutionary material

2. Provides a reserve of hereditary variability

3. The object is the phenotype of an individual

4. Provides selection of genotypes

5. Directional factor

6. Random factor

Explanation: Natural selection- selection, as a result of which (in the natural environment) the organism most adapted to given environmental conditions survives (forms of selection are distinguished: driving, stabilizing, disruptive).

Natural selection is one of the driving forces of evolution.

Characteristics:

Object - phenotype of an individual

Provides genotype selection

It is a factor of directed action (towards the formation of the most adapted organisms).

The correct answer is 345.

Task 16.

Establish a correspondence between organisms that appeared or flourished in the process of evolution and the eras in which they appeared and flourished.

Organisms

A. The emergence of the first birds

B. The heyday of reptiles

B. Shellfish bloom

G. Insect bloom

D. The rise of mammals

E. Bird distribution

Eras

1. Paleozoic

2. Mesozoic

3. Cenozoic

Explanation: Let's look at the table.

In the Paleozoic, mollusks flourished.

In the Mesozoic - the flourishing of reptiles and the appearance of the first birds (Archaeopteryx, etc.).

In the Cenozoic, insects and mammals flourished and birds spread.

The correct answer is 221333.

Task 17.

What signs characterize agrocenosis? Choose three correct answers out of six and write them down.

1. The natural cycle of substances in this community is disrupted

2. High number of plants of one species

3. A large number of plant and animal species

4. The leading factor influencing the community is artificial selection

5. Closed cycle of substances

6. Species have different adaptations for living together

Explanation: agrocenosis is an artificial ecosystem created by man. The natural cycle of substances is disrupted in it (the cycle of substances is not closed), there is a high number of plants of one species (for example, a potato field), and the leading factor is artificial selection.

The correct answer is 124.

Task 18.

Establish a correspondence between a characteristic of the environment and its factor.

Characteristic

A. Constancy of the gas composition of the atmosphere

B. Changing the thickness of the ozone screen

B. Change in air humidity

D. Change in the number of consumers

D. Change in the number of producers

Environmental factors

1. Biotic

2. Abiotic

Abiotic factors - factors of inanimate nature - constancy of the gas composition of the atmosphere, changes in the thickness of the ozone screen, changes in air humidity.

The correct answer is 111222.

Task 19.

Place the elements of the Gray Toad species classification in the correct order, starting with the smallest. Write down the corresponding sequence of numbers in your answer.

1. Class Amphibians

2. Type Chordata

3. Genus Toad

4. Animal Kingdom

5. Tailless Squad

Explanation: We arrange the taxa starting with the smallest.

Species Gray toad

Genus Toad

Tailless Squad

Class Amphibians

Type Chordata

Animal Kingdom

The correct answer is 35124.

Task 20.

Insert into the text “Nutrition in the sheet” the missing terms from the proposed list, using numerical notations. Write down the numbers of the selected answers in the text, and then enter the resulting sequence of numbers (according to the text) in the table below.

FOOD IN LEAF

Organic substances are formed in the leaf during the process of ___________ (A). Then they move along special cells of the conducting tissue - ___________ (B) - to other organs. These cells are located in a special zone of the stem cortex - ___________ (B). This type of plant nutrition is called ___________ (G), since the starting material for it is carbon dioxide, extracted by the plant from the atmosphere.

List of terms:

1. Air

2. Wood

3. Breathing

4. Lub

5. Soil

6. Sieve tube

7. Vessel

8. Photosynthesis

Explanation: Plants are characterized by the process of formation of organic substances from inorganic substances - photosynthesis. Organic substances move through conductive tissue cells - sieve tubes. They are located in the bast. This type of plant nutrition is called aerial nutrition.

The correct answer is 8641.

Task 21.

Using the Fish Reproduction table and your knowledge of biology, choose the correct statement.

1) The largest average diameter of pike eggs.

2) Baltic cod is caught by fishermen at an immature age.

3) The largest average diameter of eggs is found in carp and cod.

4) The number of stickleback eggs is the lowest, as natural selection operates: they are eaten by predators and die from diseases and random factors.

5) The carp lays the largest number of eggs, because These are the largest fish of these representatives.

Explanation: Based on the data in the table, pike eggs have the largest average diameter (2.7 mm).

Baltic cod reaches maturity at 5-9 years of age, and is caught at 3 years of age (that is, before maturity).

Statement 3 is incorrect.

Statements 4 and 5 may be true, but we do not have such data (about natural selection and fish size).

The correct answer is 12.

Task 22.

What changes in the forest ecosystem can a decrease in the number of herbivorous mammals lead to?

Explanation: possible consequences:

1. Lack of plant population control (population of “poor” areas by plants) - spread of diseases among plants.

2. Reduction in the number of 1st order consumers (due to lack of food)

3. Reduction in the number of consumers of the 2nd and 3rd orders (due to a reduction in the number of consumers of the 1st order).

Task 23.

Name the organism shown in the figure and the type to which it belongs. What is indicated by the letters A and B, name the functions of these cells.

Explanation: The picture shows a hydra, Type Coelenterata.

Hydra has two layers - outer (ectoderm) and inner (endoderm).

The letter A indicates stinging cells. The hydra releases them to catch and immobilize the victim.

The letter B indicates a digestive muscle cell (function - digestion).

Task 24.

Find errors in the given text. Indicate the number of proposals in which mistakes were made, explain them.

1. The nasal cavity is lined with ciliated epithelium.

2. The larynx is a hollow, funnel-shaped organ.

3. The nad-gor-tan-nik closes the entrance to the esophagus.

5. A cough occurs with a strong inhalation.

6. Gor-tan moves into two large bronchi.

Explanation: sentence-3 - the epiglottis (supraglottic cartilage) covers the entrance to the larynx, not the esophagus.

Sentence 5 - we cough when we exhale forcefully, and not when we inhale (when the airways are narrowed during a cold, for example. But, in general, there can be many reasons for coughing when exhaling).

Sentence 6 - the larynx passes into the trachea, and it divides into two large bronchi.

Task 25.

Adaptation of the bird skeleton for flight. Specify at least 4 characteristics.

Explanation:

1. Hollow bones

2. Double breathing - air sacs

3. Development of forelimbs into wings

4. Feather development

5. Muscular and glandular stomach

6. Keel development

7. Development of the tarsus

8. Tooth reduction

9. Reduction of the bladder and right ovary

Task 26.

Give examples of the destructive influence of humans on flora, explain how the harmful influence is expressed. Please indicate at least 4 points.

Explanation: The following human actions lead to a decrease in biological diversity:

1. Burning of forests (grass, etc.).

2. Deforestation.

3. Plowing the soil.

4. Destruction of certain plant species.

5. Destruction of plants listed in the Red Book.

6. Destruction of weeds (weeding or the use of special substances - herbicides).

7. Drainage of swamps - destruction of algae, mosses, etc.

8. Contribute to enhancing global change.

Task 27.

There are 42 chromosomes in oat somatic cells. Determine the chromosome set and the number of DNA molecules before the onset of meiosis I and in metaphase of meiosis II. Explain your answer.

Explanation: Soamtic cells of oats contain a diploid (double) set of chromosomes, and during the process of meiosis, 4 haploid cells (with a single set of chromosomes) are obtained. At the beginning of meiosis, the number of DNA molecules doubles, that is, it was 2n2c, but became 2n4c. By metaphase of meiosis II, one division has already occurred, that is, the set remains 1n2c.

Let's look at the table.

Task 28.

When corn plants with smooth, colored seeds were crossed with plants with wrinkled, uncolored seeds, the offspring ended up with smooth, colored seeds. In the analyzing cross of the F1 hybrid, the offspring of two phenotypic groups were obtained. Make a diagram for solving the problem. Determine the genotypes of parental individuals, genotypes and phenotypes of offspring in crosses. Explain the appearance of two phenotypic groups in F2. What law of heredity is manifested in F1 and F2?

Explanation: A - smooth seeds

a - wrinkled seeds

B - colored seeds

c - uncolored seeds

In the first crossing, we obtain uniformity in the offspring (all plants with smooth and colored seeds). So the crossing looks like this:

P1: AABB x aaBB

G1: AB x aw

AaBB - smooth colored seeds

Let's carry out an analysis cross (with a recessive homozygote):

P2: AaBv x aaav

G2: AB, av x av, since only two phenotypic groups were obtained in the offspring, we conclude that the genes AB and av are linked

F2: AaBB - smooth colored seeds

aavv - wrinkled uncolored seeds

5. Chromosomes, their shape, structure, chemical composition, biological role. Structure and functions of interphase and metaphase chromosomes.

6. Human karyotype. Principles of compiling idiograms.

7. Polytene chromosomes, mechanism of formation, biological significance.

8. Proteins, their chemical composition, levels of structural organization. Biological role of proteins. The concept of histone and non-histone proteins. Prion proteins and their medical significance.

9. Nucleic acids. DNA, its composition and structural organization,

10. RNA. Types of RNA, their structure and chemical composition, biological role. RNA splicing (processing), alternative splicing and RNA of structural genes of eukaryotes. The concept of ribozymes.

11. Autoreduplication of DNA: the essence of the phenomenon, the role of Enzymes, structural

12. Transcription: the essence of the phenomenon, features in pro- and eukaryotic cells. Biological significance.

13. Translation: the essence of the phenomenon, necessary components and conditions, structural features of t-RNA, minor bases and their role. Transcription enzymes. Protein processing.

15. Scheme of signal transmission into the cell, primary and secondary

16. Flows of genetic information in the cell. The phenomenon of reverse transcription. Biological role.

17. Forms of cellular reproduction of somatic cells: mitosis, amitosis, endomitosis, polyteny. The essence of the phenomenon and biological significance. Problems of cell proliferation.

18. The concept of the life cycle of a cell. Characteristics of periods.

19. Meiosis. Phases of meiosis. Features of prophase 1. Biological significance. Dynamics of chromosomes (n) and DNA (c). Scheme of violation of chromosome divergence and the formation of pathological karyotypes.

20.Mitosis and meiosis - comparative cytological characteristics

21.Gametogenesis. Comparative characteristics of the periods of ovo- and spermatogenesis: reproduction, growth, maturation and formation.

22.Gametes - eggs and sperm. Morphological, physiological and genetic characteristics. The essence of the sexual process, biological significance. Features of the sexual process in humans.

23. The concept of onto- and phylogeny. Stages of ontogenesis. Periods of embryonic development.

24.Types of eggs. The relationship between the types of eggs and the nature of fragmentation.

25. Concept of gastrula. Types of gastrulation. Derivatives of ecto- and endoderm.

26. Methods of laying down the mesoderm and its derivatives.

27. Mechanisms of cell differentiation in embryogenesis: ooplasmic segregation, embryonic induction, gene activity. The concept of homeotic genes.

28. Critical periods of embryogenesis. Teratogenic factors.

9. Nucleic acids. DNA, its composition and structural organization,

localization in the cell. Biological role.

Nucleic acids are natural high-molecular organic compounds that ensure the storage and transmission of hereditary (genetic) information in living organisms.

In nature, there are two types of nucleic acids, differing in composition, structure and functions. One of them contains the carbohydrate component deoxyribose and is called deoxyribonucleic acid (DNA). The other contains ribose and is called ribonucleic acid (RNA).

DNA, its composition

DNA is a double-stranded biological polymer whose monomers are nucleotides containing one of the nitrogenous bases, deoxyribose and a phosphoric acid residue. DNA nucleotides: purine bases adenine (A) and guanine (G) and pyrimidine bases cytosine (C) and thymine (T).

structural organization

The polynucleotide chains of the DNA molecule are antiparallel and connected to each other by hydrogen bonds according to the principle of complementarity to form a double helix.

localization in the cell

DNA is found in the cell nucleus in the form of a complex with nuclear proteins (histones). There is also its own special (circular) DNA in mitochondria (mtDNA) and in chloroplasts in plants (chlDNA). Bacteria do not have a nucleus, therefore DNA floats freely in the cytosol (intracellular fluid, cytoplasmic matrix).

Biological role

DNA has one function - storing genetic information.

10. RNA. Types of RNA, their structure and chemical composition, biological role. RNA splicing (processing), alternative splicing and RNA of structural genes of eukaryotes. The concept of ribozymes.

Unlike DNA molecules, ribonucleic acids are represented by a single polynucleotide chain, which consists of four types of nucleotides containing sugar, ribose, phosphate and one of four nitrogenous bases - adenine, guanine, uracil or cytosine. RNA is synthesized on DNA molecules using RNA polymerase enzymes in compliance with the principle of complementarity and antiparallelism, and uracil is complementary to DNA adenine in RNA. The entire variety of RNAs operating in the cell can be divided into three main types: mRNA, tRNA, rRNA.

Matrix, or information, RNA (mRNA, or mRNA).

Transcription. In order to synthesize proteins with specified properties, “instructions” are sent to the site of their construction about the order of inclusion of amino acids in the peptide chain. This instruction is contained in the nucleotide sequence of matrix, or messenger RNA (mRNA, mRNA), synthesized in the corresponding sections of DNA. The process of mRNA synthesis is called transcription. The synthesis of mRNA begins with the detection by RNA polymerase of a special region in the DNA molecule, which indicates the place where transcription begins - the promoter.

After binding to the promoter, RNA polymerase unwinds the adjacent turn of the DNA helix. Two DNA strands diverge at this point, and on one of them the enzyme synthesizes mRNA. The assembly of ribonucleotides into a chain occurs in compliance with their complementarity to DNA nucleotides, and also antiparallel with respect to the DNA template strand. Due to the fact that RNA polymerase is capable of assembling a polynucleotide only from the 5" end to the 3" end, only one of the two DNA strands, namely the one facing the enzyme with its 3" end, can serve as a template for transcription ( 3" → 5"). Such a chain is called codogenic. The antiparallel connection of two polynucleotide chains in a DNA molecule allows RNA polymerase to correctly select the template for the synthesis of mRNA. Moving along the codogenic DNA chain, RNA polymerase carries out gradual accurate rewriting of information until it does not encounter a specific nucleotide sequence - the transcription terminator. In this region, the RNA polymerase is separated from both the DNA template and the newly synthesized mRNA. A fragment of the DNA molecule, including the promoter, the transcribed sequence and the terminator, forms a transcription unit - transcripton. , as RNA polymerase moves along the DNA molecule, the single-stranded DNA sections it has traversed are again combined into a double helix. The mRNA produced during transcription contains an exact copy of the information recorded in the corresponding section of DNA. Triples of adjacent mRNA nucleotides that encode amino acids are called codons. The codon sequence of the mRNA encodes the sequence of amino acids in the peptide chain. mRNA codons correspond to specific amino acids. The template for mRNA transcription is the codogenic DNA strand, which faces the enzyme with its 3" end

Transfer RNA (tRNA). Broadcast. Transfer RNA (tRNA) plays an important role in the process of using hereditary information by a cell. By delivering the necessary amino acids to the site of assembly of peptide chains, tRNA acts as a translational intermediary. tRNA molecules are polynucleotide chains synthesized from specific DNA sequences. They consist of a relatively small number of nucleotides -75-95. As a result of the complementary combination of bases that are located in different parts of the tRNA polynucleotide chain, it acquires a structure resembling a clover leaf in shape. It has four main parts that perform different functions. The acceptor “stem” is formed by two complementary connected terminal parts of tRNA. It consists of seven base pairs. The 3" end of this stem is slightly longer and forms a single-stranded region that ends with a CCA sequence with a free OH group. The transported amino acid is attached to this end. The remaining three branches are complementary paired nucleotide sequences that end in unpaired regions that form loops. The middle one of these branches - the anticodon - consists of five pairs of nucleotides and contains an anticodon in the center of its loop. The anticodon is three nucleotides complementary to the mRNA codon, which encodes the amino acid transported by this tRNA to the site of peptide synthesis; two side branches are located between the acceptor and anticodon branches. In their loops they contain modified bases - dihydrouridine (D-loop) and a triplet TψC, where \y is pseudouraine (T^C-loop) There is an additional loop between the aiticodone and T^C branches, including from 3-5 to 13. -21 nucleotides. In general, different types of tRNA are characterized by a certain constancy of the nucleotide sequence, which most often consists of 76 nucleotides. The variation in their number is mainly due to changes in the amount

nucleotides in the extra loop. The complementary regions that support the tRNA structure are usually conserved. The primary structure of the tRNA, determined by the nucleotide sequence, forms the secondary structure of the tRNA, which is shaped like a clover leaf. In turn, the secondary structure determines the three-dimensional tertiary structure, which is characterized by the formation of two perpendicularly located double helices. One of them is formed by the acceptor and TψC branches, the other by the anticodon and D branches. The transported amino acid is located at the end of one of the double helices, and the anticodon is located at the end of the other. These areas are located as far as possible from each other. The stability of the tertiary structure of tRNA is maintained due to the occurrence of additional hydrogen bonds between the bases of the polynucleotide chain, located in different parts of it, but spatially close in the tertiary structure. Different types of tRNA have similar tertiary structures, although with some variations. One of the features of tRNA is the presence of unusual bases in it, which arise as a result of chemical modification after the inclusion of a normal base in the polynucleotide chain. These altered bases determine the great structural diversity of tRNAs in the general plan of their structure. Of greatest interest are modifications of the bases forming the anticodon, which affect the specificity of its interaction with the codon. For example, the atypical base inosine, sometimes found in the 1st position of the tRNA anticodon, is capable of complementarily combining with three different third bases of the mRNA codon - U, C and A. The existence of several types of tRNA that can bind to the same codon has also been established. As a result, in the cytoplasm of cells there are not 61 (by the number of codons), but about 40 different tRNA molecules. This amount is enough to transport 20 different amino acids to the site of protein assembly. Along with the function of accurately recognizing a specific codon in mRNA, the tRNA molecule delivers a strictly defined amino acid, encrypted using a given codon, to the site of synthesis of the peptide chain. The specific connection of tRNA with its “own” amino acid occurs in two stages and leads to the formation of a compound called aminoacyl-tRNA.

Attaching an amino acid to the corresponding tRNA:

I-1st stage, interaction of amino acid and ATP with the release of pyrophosphate;

II-2nd stage, attachment of adenylated amino acid to the 3" end of RNA

At the first stage, the amino acid is activated by interacting its carboxyl group with ATP. As a result, an adepylated amino acid is formed. At the second stage, this compound interacts with the OH group located at the 3" end of the corresponding tRNA, and the amino acid attaches to it with its carboxyl group, releasing AMP. Thus, this process occurs with the expenditure of energy obtained from the hydrolysis of ATP to AMP The specificity of the connection between an amino acid and a tRNA carrying the corresponding anticodon is achieved due to the properties of the aminoacyl-tRNA synthetase enzyme. In the cytoplasm, there is a whole set of enzymes that are capable of spatial recognition, on the one hand, of their amino acid, and on the other, of the corresponding tRNA anticodon. . Hereditary information, “recorded” in DNA molecules and “rewritten” on mRNA, is deciphered during translation due to two processes of specific recognition of molecular surfaces. First, the enzyme aminoacyl-tRNA synthetase ensures the connection of the tRNA with the amino acid it transports. Then the aminoacyl-tRNA complementarily pairs with it. mRNA due to anticodon-codon interaction. Using the tRNA system, the language of the nucleotide chain of mRNA. translated into the language of the amino acid sequence of the peptide. Ribosomal RNA (rRNA). Ribosomal cycle of protein synthesis. The process of interaction between mRNA and tRNA, which ensures the translation of information from the language of nucleotides to the language of amino acids, is carried out on ribosomes. The latter are complex complexes of rRNA and various proteins, in which the former form a framework. Ribosomal RNAs are not only a structural component of ribosomes, but also ensure their binding to a specific nucleotide sequence of mRNA. This establishes the start and reading frame for the formation of the peptide chain. In addition, they ensure the interaction between the ribosome and tRNA. Numerous proteins that make up ribosomes, along with rRNA, perform both structural and enzymatic roles.

1. Messenger RNA transfers the genetic code from the nucleus to the cytoplasm, thus determining the synthesis of various proteins.

2. Transfer RNA carries activated amino acids to ribosomes for the synthesis of polypeptide molecules.

3. Ribosomal RNA in complex with approximately 75 different proteins forms ribosomes - cellular organelles on which polypeptide molecules are assembled.

4. Small nuclear RNAs (introns) Participates in splicing.

5. Small cytoplasmic RNAs

6. snoRNA. She is a small nucleolus. In the nucleoli of eukaryotic cells.

7. RNA viruses

8. Viroid RNA

After polyadenylation, the mRNA undergoes splicing, during which introns (regions that do not code for proteins) are removed, and exons (regions that code for proteins) are stitched together to form a single molecule. Splicing is catalyzed by a large nucleoprotein complex, the spliceosome, consisting of proteins and small nuclear RNAs. Many pre-mRNAs can be spliced in different ways to produce different mature mRNAs encoding different amino acid sequences (alternative splicing).

Briefly: splicing is when introns that do not code for anything leave and a mature molecule capable of encoding a protein is formed from exons.

Alternative splicing - different proteins can be obtained from one pre-mRNA molecule. That is, we are dealing with variations in intron loss and different exon stitching.

Ribozymes

RNA molecules with enzymatic activity (usually autocatalysis)

Regulation of gene expression by antisense RNAs is characterized by high specificity. This is due to the high accuracy of the RNA-RNA hybridization process, based on the complementary interaction of extended nucleotide sequences with each other.

However, antisense RNAs themselves do not irreversibly inactivate target mRNAs, and high intracellular concentrations of antisense RNAs are required to suppress the expression of the corresponding genes. The effectiveness of antisense RNAs increased sharply after they were supplemented with ribozyme molecules - short RNA sequences with endonuclease activity. Many other enzymatic activities associated with RNA are known. Therefore, ribozymes in the broad sense are called RNA molecules that have any enzymatic activity.

The RNA variant of suppressing HIV infection was tested on model systems. For this purpose, an unusual property of some RNA molecules is used - their ability to destroy other types of RNA. Americans T. Cech and S. Altman received the Nobel Prize in 1989 for this discovery. It was believed that all biochemical reactions in the body occur thanks to highly effective specific catalysts, which are proteins - enzymes. However, it turned out that some types of RNA, like proteins, have highly specific catalytic activity. These RNAs were called ribozymes.

Ribozymes contain antisense regions and sites that carry out enzymatic reactions. Those. They not only attach to the mRNA, but also cut it. The essence of the method of suppressing HIV infection with the help of ribozymes is shown in Fig. 32. By attaching to a complementary target RNA, the ribozyme cleaves this RNA, resulting in the cessation of synthesis of the protein encoded by the target RNA. If such a target for the ribozyme is viral RNA, then the ribozyme will “spoil” it, and the corresponding viral protein will not be formed. As a result, the virus will stop reproducing in the cell. This approach is also applicable to some other human pathologies, for example, for the treatment of cancer.

Bacteria and blue-green algae, which are usually classified as prokaryotes (that is, prenuclear living organisms), are characterized by the presence of a bacterial chromosome. This is a conventional name that hides a single circular DNA molecule. It is present in all prokaryotic cells and is located directly in the cytoplasm, without a protective shell.

As becomes clear from the definition of prokaryotes, the main quality of their structure is the absence of a nucleus. The circular DNA molecule is responsible for storing and transmitting all the information that a new cell created during division will need. The structure of the cytoplasm is very dense and immobile. It lacks a number of organelles that perform important functions in eukaryotic cells:

mitochondria,
lysosomes,
endoplasmic reticulum,
plastids,
Golgi complex.

Ribosomes, which are “busy” in the production of proteins, are randomly located in the cytoplasm. The mission of energy production is also important. Its synthesis occurs in mitochondria, but the structure of bacteria excludes their presence. Therefore, the function of these organelles was taken over by the cytoplasm.

Mitochondria have one feature that makes them somewhat similar to bacteria - they store mitochondrial DNA. Its structure resembles bacterial chromosomes. DNA in mitochondria is assembled into a separate circular nucleoid. Some particularly long organelles may contain up to ten such molecules. When the fission process begins in such mitochondria, a section containing one nucleoid is separated from them. And in this one can also find similarities with the binary fission of bacteria.

Genome of microorganisms

The process of self-replication, during which important data is copied from one source to another, is called replication. The result of this action (also characteristic of bacterial cells) is the creation of a similar structure. Replication participants (replicons) in prokaryotes are:

circular DNA molecule
plasmids.

DNA nucleotides in bacterial cells are located in a certain sequence. This structure allows you to arrange the order of amino acids in the protein. Each gene contains a unique number and arrangement of nucleotides.

All properties and characteristics of prokaryotes are determined by their complex of genes (genotype). If we talk about microorganisms, then for them the genotype and genome are practically synonymous.

The phenotype is the result of the interaction of a set of genes and environmental conditions. It depends on specific environmental conditions, but is controlled directly by the genotype. This is due to the fact that all possible changes are already determined by the set of genes that make up the section of the circular DNA molecule.

The genotype can change not only depending on environmental influences. Various mutations or rearrangements of genes in the structure of the DNA molecule can lead to its modification. Based on this, non-hereditary (environmental) variability and hereditary (modification) form of genotype changes are distinguished. If the nucleotides in a circular DNA molecule are rearranged or partially lost due to mutation, then this structure will be irreversible. And when environmental factors become the “culprit” of changes, then with their elimination the newly acquired qualities will disappear.

Bacterial chromosome

The circular DNA molecule in the cells of different representatives of the class of bacteria differs in size. But it has a similar structure, as well as functions, in all cases.

Prokaryotes always have one bacterial chromosome.
It is located in the cytoplasm.
If in the cells of eukaryotes the DNA molecule has a linear structure and is considered longer (it has up to 1010 base pairs), then in bacteria it is closed in a ring. And the bacterial chromosome of prokaryotes is shorter (5106 base pairs).
One circular DNA molecule contains information about all the necessary functions for the life of bacteria. These genes can be divided into 10 groups (based on the processes they control in the cell). You can display this classification as a table.

Life processes in prokaryotic cells	The number of studied genes that are located in the bacterial cell and are responsible for certain processes
Delivery of various compounds and nutrients to the cell	92
Carrying out the synthesis of phospholipids, fatty and amino acids, nucleotides, vitamins and other compounds	221
Organization of the apparatus for protein synthesis	164
Shell synthesis	42
Breakdown of complex organic substances and other reactions to produce energy	138
Catabolism (processing, breakdown) of macromolecules of proteins, carbohydrates and fats	22
The ability of directed movement towards useful substances and away from an irritant (chemotaxis), the mobility of bacteria in general	39
Production of ATP (a universal form of chemical energy inherent in any living cell). As mentioned earlier, this process in eukaryotes occurs in mitochondria and is the main activity for these organelles	15
Replication of nucleic acids, including genes	49
Other genes, including those with unstudied functions	110

In general, one chromosome can carry about 1000 known genes.

Plasmids

Another replicon of prokaryotes are plasmids. In bacteria, they are DNA molecules with a structure in the form of two chains closed in a ring. Unlike the bacterial chromosome, they are responsible for encoding those “skills” of the bacterium that will help it survive if it suddenly finds itself in unfavorable conditions for its existence. They can autonomously reproduce themselves, so there may be several copies of plasmids in the cytoplasm.

Transmissible replicons are capable of being transmitted from one cell to another. They carry in their circular DNA molecule some characteristics that are classified as phenotypic changes:

development of antibiotic resistance;
the ability to produce colicins (protein substances capable of destroying microorganisms of the same kind that served as the source of their occurrence);
processing of complex organic substances;
synthesis of antibiotic substances;
the ability to penetrate the body and cause diseases;
the ability to overcome defense mechanisms, multiply and spread in the body;
ability to produce toxins.

The last three “skills” are called pathogenicity factors, knowledge of which is contained in the circular DNA molecule of plasmids. It is thanks to these factors that pathogenic bacteria become dangerous to the human body.

Thus, the circular DNA molecule, found in all prokaryotes, alone carries within itself a whole set of skills useful for their survival and vital activity.

In prokaryotic cells, deoxyribonucleic acid is located in a cytoplasmic colloidal (“glue”) matrix along with other components. The ground substance contains this type of nucleic acid, represented by a double-stranded helix, in chromosomes. Otherwise it is called covalently closed circles DNA (abbreviated as cccDNA).

Bacterial chromosomes are less condensed. They float freely in the cytoplasmic matrix within a small nuclear region - the nucleoid. Moreover, they are curled into supercoiled “balls”. If you stretch one of the chains in length, it will be 1000 times larger than the size of the cell itself! It can be wrapped around a protein.

Bacterial macromolecules as cytoplasmic inclusions are covered with histone-like proteins: H-NS, HU, JHF, FIS. But the density of this “shell” is very small. Only some archaea from the euarchaea group have nucleosomes.

The size of the bacterial genetic macromolecule ranges from 600 thousand (for mycoplasma - Mycoplasma) to 10 million (for myxococci) nucleotide pairs. Prokaryotes are haploid. Their single chromosomes have a circular or linear (in three species: Borrelia, Streptomyces, Rhodococcus) shape.

The genetic material in prenuclear cells consists of many loops emanating from a single center. Due to the absence of an envelope in the nucleoid, these domains penetrate even into the peripheral cytoplasm. This feature significantly affects the transcription process.

Prokaryotic chromosomes are attached to the cell membrane. They have quite a lot of attachment points:

oriC - “origin of the chromosome” - point of origin of replication;
terC - “terminus of the chromosome” - termination point;
replication fork.

Places of attachment are divided into permanent and sliding. Prokaryotic genes are grouped into operons. The unifying features are the similarity of functions and the unity of promoters. The latter are sets of gene nucleotides, upon exposure to which the transcription process is launched. Structural genes take up significantly more space than regulatory genes.

Some segments of “hereditary” molecules are able to move within a prokaryotic cell between genetic loci - these are transposons. There are two types of such moving elements:

IS elements are the simplest modules of transposase genes;
Tn elements are actually transposons.

The former move randomly and are extremely mobile. The longer the transposon, the more passive it is. The genetic elements of prokaryotes are not only chromosomes, transposons, but also plasmids. They are completely autonomous extrachromosomal molecules. Transposons should not be confused with plasmids, because the former cannot exist independently of chromosomes.

Thus, the peculiarities of the localization of hereditary information in prokaryotes are associated with the absence of a membrane in the nucleoid, as well as in some organelles. Segments with hereditary information are localized near the nuclear region, and are also “stretched” throughout the peripheral cytoplasm.

Localization of DNA in eukaryotic cells

The localization of deoxyribonucleic acid molecules near the cellular “center” was first established by Feulgen using the Schiff reaction closer to the middle of the twentieth century. Spatially, DNA molecules are localized by proteins - histones. Such complexes are called nucleosomes.

Eukaryotic chromosomes are localized mainly in the nucleolus of the nucleus, although it does not have its own membrane. The molecules are associated with chromatin. If we compare it with prenuclear organisms, here genetic macromolecules are not represented by transposons moving freely in the cytoplasm, as well as plasmids. But eukaryotes have hereditary molecules in organelles: mitochondria, plastids.

Mitochondrial DNA (abbreviated as mtDNA) no longer constitutes the nuclear genome, but a cytoplasmic plasmon. Most eukaryotes have mitochondria: plants, fungi, animals. In the cytoplasm they move to where energy demand increases.

Types of mitochondria:

young – protomitochondria;
mature;
old - postmitochondria.

Carriers of hereditary characteristics are located in a matrix bounded by a second, internal membrane. Otherwise it is called pink substance. mtDNA has a linear and/or closed circular shape. It is much smaller than a nuclear one. Maxi- and minicircles of mitochondrial DNA can combine to form catenanes. The coding sequences of the mitochondrial genome are called codons.

If there are several mitochondria, then they have identical and unique types of macromolecules. mt-DNA is most often inherited through the maternal line. There are eukaryotes with mitochondria that do not contain genetic macromolecules - mitosomes.

Mitochondria are not the only organelles of eukaryotes that have their own genetic apparatus. The plastid genome is called the plastome or pDNA. In these semi-autonomous organelles, operons are created by analogy with the cellular formations of eukaryotes. Genetic carriers are located in the plastid matrix - the stroma.

Usually, when talking about the plastid genome, they mean chloroplasts and their cDNA. But there are many more types of plastids:

propplastids;
leukoplasts;
amyloplasts;
elaioplasts;
proteinoplasts;
etioplasts - dark plastids;
chloroplasts;
chromoplasts.

In a simplified manner, the features of DNA localization in “prenuclear” and eukaryotic organisms can be represented using the table:

Genetic elements are found in non-cellular forms - viruses. Their localization and quantity in varieties of prenuclear/nuclear smallest units of life are very diverse. The similarity of prokaryotic and eukaryotic cells indicates that these are elementary structural and functional units of living matter, as well as the unity of the origin of life on Earth. The existing differences in the localization of macromolecules confirm the evolutionary theory.

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