Eukaryotes have a formed nucleus containing DNA. The size of a typical eukaryotic cell, such as a human liver cell, is ~25 µm across. Its core, measuring ~5 µm in diameter, contains 46 chromosomes, the total length of DNA of which is 2 m. Eukaryotes contain significantly more DNA than prokaryotes. Thus, human and other mammalian cells contain 600 times more DNA than E. coli. The total length of all DNA isolated from the cells of an adult human body is ~ 2 x 10 13 m or 2 x 10 10 km, which exceeds the circumference of the globe (4 x 10 4 km) and the distance from the Earth to the Sun (1.44 x 10 8 kilometers).

The development of single-molecule localization microscopy techniques has enabled nanometer-scale localization precision within cells, allowing resolution of ultrafine cellular structure and elucidation of critical molecular mechanisms. The development of single-molecule localization microscopy, particularly for high-resolution imaging, has allowed researchers to visualize biological processes occurring at scales below the diffraction limit. The resulting localizations can subsequently be reconstructed into a pointillist image with a spatial resolution more than 10 times the scale of broadband microscopy.

In eukaryotes, DNA is found in chromosomes. Human cells have 46 chromosomes (chromatids), which are organized into 23 pairs. Each chromosome of a eukaryotic cell contains one very large double-stranded DNA molecule carrying a set of genes. The totality of a cell's genes makes up its genome. Genes- these are sections of DNA that encode polypeptide chains and RNA.

The application of single-molecule microscopy to understand phenomena that do not exhibit any ordered structure has been largely limited to prokaryotes, exploiting their physical dimensions through techniques such as total internal reflection fluorescence microscopy.

This is partly due to the lack of specific methods to overcome the problems associated with greater depth of field. It provides researchers with the ability to perform complex genetic experiments with the relative technical ease of a single-celled organism, being more closely related to humans than prokaryotes.

The DNA molecules in the 46 human chromosomes are not the same size. The average length of a chromosome is 130 million base pairs and has a length of 5 cm. It is clear that it is possible to fit DNA of this length into the nucleus only through its specific packaging. When the tertiary structure of human DNA is formed, its size decreases on average by 100 thousand times.

Each laser line imaged a quarter-wave plate and a low-pass filter. Both laser beams were expanded and collimated using an integrated beam expander consisting of two matching lenses and coupled using a dichroic mirror.

A multiband dichroic mirror, a bandpass filter, and a long filter were used to separate the fluorescence signal from the laser light. After incubation, the cells were then washed three times and resuspended in ice-cold phosphate buffered saline. Immediately before imaging, cells were placed on a 1% agarose pad and sandwiched between two ozonated coverslips, which were then sealed with paraffin wax.

The packaging of DNA in eukaryotic chromosomes is different from its packaging in prokaryotic chromosomes. Eukaryotic DNA does not have a circular, but a linear, double-stranded structure. In addition, the tertiary structure of DNA in eukaryotic cells differs in that multiple helicalization of DNA is accompanied by the formation of complexes with proteins. Eukaryotic DNA contains exons- regions encoding polypeptide chains, and introns– non-coding regions (perform a regulatory function).

The simulation creates an image by randomly positioning molecules and simulating fluorescent photon emissions and molecular diffusion over time using customized intervals. Simulation steps were integrated into a given exposure time, allowing diffusing molecules to move within a single output frame. Each pixel was subjected to Poisson noise. Background noise, fluorophore intensity, and blink parameters were modeled to match the experimental values ​​observed under our optimized imaging conditions.

Eukaryotic chromosomes are made up of chromatin fibers.

Eukaryotic chromosomes appear as sharply defined structures only immediately before and during mitosis, the process of nuclear division in somatic cells. In resting, non-dividing eukaryotic cells, chromosomal material called chromatin, looks fuzzy and seems to be randomly distributed throughout the core. However, as a cell prepares to divide, chromatin becomes compacted and assembled into chromosomes.

Nucleases and ligases

For each simulation, a total of 500 molecules were simulated and randomly placed into confined spherical regions of 2 μm in diameter to simulate the confinement of the yeast fission nucleus. Diffusion molecules were modeled in three dimensions at a depth of 2 μm, similar to the depth of a yeast cell. Static molecules were modeled in two dimensions within the confinement to simulate static molecules in the focal plane. The simulated data were fitted with our 2D Gaussian routines and the results compared to known simulation positions.

Chromatin consists of very thin fibers that contain ~60% protein, ~35% DNA, and probably ~5% RNA. The chromatin fibers in the chromosome are folded and form many knots and loops. DNA in chromatin is tightly bound to histone proteins, whose function is to package and organize DNA into structural units - nucleosomes. Chromatin also contains a number of non-histone proteins. Chromatin fibers resemble strings of beads in appearance. Beads are nucleosomes .

Recall that single molecules were measured by calculating the percentage of molecules that were correctly localized at least once within 50 nm of the true position. Analysis using recall of all localizations showed similar results.

Noise in an image was estimated by calculating the sum of the differences of each pixel with its four immediate neighbors divided to form the pixel's residual. The least half squared residuals were then summed and used to estimate noise. This method provided a very stable noise estimate regardless of the number of spots present in a given frame. Peaks appearing in adjacent frames within a threshold distance of 800 nm were considered to belong to the same molecular trajectory.

The nucleosome consists of histone proteins. Each nucleosome contains 8 histone molecules - 2 H2A molecules. H2B, H3, H4. Double-stranded DNA wraps around the nucleosome twice.

The DNA strand is wound around the outside of the histone core of the nucleosome. In the spaces between the nucleosomes there is a connecting strand of DNA, to which histone H1 binds. Thus, nucleosomes are structural units of chromatin that perform the function of dense packaging of DNA. (DNA is shortened by wrapping around histones.) Chromatin is also associated with non-histone nuclear proteins, which form the nuclear matrix.

Fluorescence correlation spectroscopy

Individual traces of single diffusion proteins consisting of at least four steps were saved for further diffusion analysis by calculating their root mean square displacement. Therefore, we simulated three-dimensional Brownian motion inside a sphere of 1 μm radius to obtain a more accurate diffusion coefficient inside the core. The number of molecules per field of view was adjusted to be suitable for single particle tracking analyses. We hypothesized that there would be no significant change in the diffusion coefficient of the fusion proteins due to the nearly identical structures and molecular weights of the two fluorescent reporters.

Eukaryotic cells also contain cytoplasmic DNA .

In addition to DNA in the nucleus, eukaryotes have DNA in mitochondria. The chloroplasts of photosynthetic cells also contain DNA. Typically, the DNA in the cytoplasm makes up 0.1% of the total cellular DNA.

Mitochondrial DNA- These are small double-stranded ring molecules.

For all experiments, microscope glass slides were thoroughly cleaned before use. Borosilicate coverslips No. 1 were first ozonated for 30 min to remove traces of autofluorescence. Cells were plated on a 5% agarose pad sandwiched between two ozonated coverslips sealed with paraffin wax. Experiments were performed at 0 ± 5 °C with a low excitation power of 45 μW in the sample to reduce the effect of photobleaching during the experiment.

A solution of 10 nM commercial fluorescein was used to calibrate the detection volume. Using extended exposure times allowed us to separate the fluorescent signal arising from scattering and quiescent populations: unbound proteins that diffuse rapidly emit a fluorescent signal from multiple separated physical locations in the sample during the exposure time of each acquired frame.

Molecules DNA in chloroplasts significantly more than in mitochondria.

The DNA of mitochondria and chloroplasts is not associated with histones.

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.

At short time intervals, fluorescence from individual scattering molecules is expected to appear as a separate puncture and therefore be indistinguishable from static molecules. This will not differentiate between cell cycle stages. However, as exposure time increases, fluorescence from scattering molecules is expected to become increasingly diffuse.

Molecular diffusion modeling to optimize exposure time

The time for which single fluorophores were imaged followed an exponential distribution with a mean time of 40 ms and the 95th percentile of localizations falling at 97 ms. The reduction in detection of bound molecules at higher exposure times is likely to be due to the ongoing integration of background signal, limiting the localization detected above background to a small population of long-lived fluorophores. An advantage of yeast as a model eukaryote is the ease with which complex genetic experiments can be performed to elucidate important relationships between gene function and phenotype.

Features of prenuclear microorganisms

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 the preservation and transmission of all information that will be needed by a new cell created during the division process. The structure of the cytoplasm is very dense and immobile. It does not contain a number of organelles that perform important functions in:

However, future use of these technologies will rely on the development of robust methodological tools that allow specific phenomena to be directly characterized and visualized. However, there is no a priori reason why the method cannot be extended to other eukaryotes. One limitation of our approach is that because chromatin moves during the acquisition time, the reconstructed snapshots do not provide spatial information about protein localization in the cell at any point in time.

• 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.

Indeed, the yield is largely limited to the quantitative measurement, which is the chromatin-associated protein fraction, which can only be interpreted between two or more specific conditions. All authors contributed to the design of the experiments. B. conducted experiments with a microscope. E. analyzed the localization numbers, reconstructed high-resolution images and performed simulations. B performed single-particle tracking analysis. G. designed and built a microscope.

Structures at the ends of chromosomes

†The authors would like to know that they believe the first two authors should be considered joint first authors. Open access fee funding: European Research Council. Conflict of interest. Obtaining intracellular fluorescent proteins with nanometer resolution. Super-resolution using fluorescence photoactivation localization microscopy.

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:

Components of prokaryotic cells

A prokaryote is a simple, single-celled organism that lacks an organized nucleus or other membrane-bound organelle. Describe the structure of prokaryotic cells. All cells have four common components. General structure of a prokaryotic cell. This figure shows the generalized structure of a prokaryotic cell. The other structures shown are present in some, but not all, bacteria.

However, prokaryotes differ from eukaryotic cells in several ways. A prokaryote is a simple, single-celled organism that lacks an organized nucleus or any other membrane-bound organelle. We will soon see that this is significantly different in eukaryotes.

• circular DNA molecule
• plasmids.

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.

Most prokaryotes have a peptidoglycan cell wall, and many have a polysaccharide capsule. The cell wall acts as an additional layer of protection, helps the cell maintain its shape and prevents dehydration. The capsule allows the cell to attach to surfaces in the environment. Some prokaryotes have flagella, pili, or fimbriae. Pili are used to exchange genetic material during reproduction, called conjugation. With a diameter of 1 to 0 µm, prokaryotic cells are significantly smaller than eukaryotic cells with a diameter of 10 to 100 µm.

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.

The small size of prokaryotes allows ions and organic molecules to enter them so that they quickly diffuse to other parts of the cell. Likewise, any waste produced in a prokaryotic cell can quickly diffuse out. This is not the case for eukaryotic cells, which have developed various structural adaptations to improve intracellular transport.

Size of Microorganisms: This figure shows the relative sizes of microbes on a logarithmic scale. Small size is, in general, necessary for all cells, whether prokaryotic or eukaryotic. First, we'll look at the area and volume of a typical cell. Not all cells are spherical, but most tend to approximate a sphere. Thus, as the radius of a cell increases, its surface area increases as the square of its radius, but its volume increases as the cube of its radius. Therefore, as the size of a cell increases, its surface area to volume ratio decreases.

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.

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.

1. Prokaryotes always have one bacterial chromosome.
2. It is located in the cytoplasm.
3. 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).
4. 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.

Topic: “Structure of eukaryotic cells.”

Choose one correct answer.

A1. There are no mitochondria in cells

2) staphylococcus

A2. Participates in the removal of biosynthetic products from the cell

1) Golgi complex

2) ribosomes

3) mitochondria

4) chloroplasts

A3. In potato tubers, starch reserves accumulate in

1) mitochondria

2) chloroplasts

3) leucoplasts

4) chromoplasts

A4. The nucleolus is the site of formation

2) chromosomes

3) lysosomes

4) ribosomes

A5. Chromatin is found in

2) ribosomes

3) Golgi apparatus

4) lysosomes

A6. The function of intracellular digestion of macromolecules belongs to

1) ribosomes

2) lysosomes

4) chromosomes

A7. The ribosome is an organelle actively involved in

1) protein biosynthesis

2) ATP synthesis

3) photosynthesis

4) cell division

A8. The nucleus in a plant cell was discovered

1) A. Levenguk

3) R. Brown

4) I. Mechnikov

A9. Non-membrane components of the cell include

2) Golgi apparatus

4) ribosome

A10. Cristas are available in

1) vacuoles

2) plastids

3) chromosomes

4) mitochondria

A11. The movement of a single-celled animal is ensured by

1) flagella and cilia

2) cell center

3) cell cytoskeleton

4) contractile vacuoles

A12. DNA molecules are found in chromosomes, mitochondria, and chloroplasts of cells

1) bacteria

2) eukaryotes

3) prokaryote

4) bacteriophages

A13. All prokaryotic and eukaryotic cells have

1) mitochondria and nucleus

2) vacuoles and Golgi complex

3) nuclear membrane and chloroplasts

4) plasma membrane and ribosomes

A14. The cell center in the process of mitosis is responsible for

1) protein biosynthesis

2) chromosome spiralization

3) movement of cytoplasm

4) formation of a fission spindle

A15. Lysosome enzymes are produced in

1) Golgi complex

2) cell center

3) plastids

4) mitochondria

A16. The term cell was introduced

1) M. Schleiden

2) R. Hooke

3) T. Schwann

4) R. Virkhov

A17. The nucleus is absent in cells

1) Escherichia coli

2) protozoa

4) plants

A18. Cells of prokaryotes and eukaryotes differ in the presence

2) ribosomes

A19. A eukaryotic cell is

1) lymphocyte

2) influenza virus

3) plague bacillus

4) sulfur bacteria

A20. The cell membrane consists of

1) proteins and nucleic acids

2) lipids and proteins

3) only lipids

4) only carbohydrates

A21. The cells of all living organisms have

2) mitochondria

3) cytoplasm

4) cell wall

IN 1. Choose three correct answers out of six. An animal cell is characterized by the presence

1) ribosomes

2) chloroplasts

3) decorated core

4) cellulose cell wall

5) Golgi complex

6) one ring chromosome

AT 2. Choose three correct answers out of six. In what structures of eukaryotic cells are DNA molecules localized?

1) cytoplasm

3) mitochondria

4) ribosomes

5) chloroplasts

6) lysosomes

AT 3. Choose three correct answers out of six. Characteristic of a plant cell

1) absorption of solid particles by phagocytosis

2) the presence of chloroplasts

3) the presence of a formed core

4) the presence of a plasma membrane

5) absence of a cell wall

6) the presence of one ring chromosome

AT 4. Choose three correct answers out of six. What is the structure and function of mitochondria?

1) break down biopolymers into monomers

2) characterized by an anaerobic method of obtaining energy

4) have enzymatic complexes located on the cristae

5) oxidize organic substances to form ATP

6) have outer and inner membranes

AT 5. Choose three correct answers out of six. The similarity between bacterial and animal cells is that they have

1) decorated core

2) cytoplasm

3) mitochondria

4) plasma membrane

5) glycocalyx

6) ribosomes

AT 6. Choose three correct answers out of six. Characteristic of an animal cell

1) the presence of vacuoles with cell sap

2) the presence of chloroplasts

3) capture of substances by phagocytosis

4) division by mitosis

5) presence of lysosomes

6) lack of a formalized core

AT 7. In a plant cell, unlike an animal cell, there are

1) ribosomes

2) chloroplasts

3) centrioles

4) plasma membrane

5) cellulose cell wall

6) vacuoles with cell sap

AT 8. Establish a correspondence between a trait and a group of organisms

A) absence of a nucleus 1) prokaryotes

B) the presence of mitochondria 2) eukaryotes

B) lack of EPS

D) presence of the Golgi apparatus

D) the presence of lysosomes

E) linear chromosomes consisting of DNA and protein

AT 9. Establish a correspondence between the trait of an organism and the kingdom for which this trait is characteristic

A) according to the method of nutrition, they are mainly autotrophs 1) Plants

B) have vacuoles with cell sap 2) Animals

B) there is no cell wall

D) cells contain plastids

D) most are able to move

E) according to the method of nutrition, they are predominantly heterotrophs

AT 10 O'CLOCK. Establish a correspondence between the presence of the named organelles in bacterial and animal cells.

A) mitochondria 1) animal liver cell

B) cell wall 2) bacterial cell

D) Golgi apparatus

D) nucleoid

E) flagella

AT 11. Establish a correspondence between cell structures and their functions

A) protein synthesis 1) cell membrane

B) lipid synthesis 2) EPS

B) division of the cell into sections (compartments)

D) active transport of molecules

D) passive transport of molecules

E) formation of intercellular contacts

AT 12. Place the events listed in chronological order.

A) Inventions of the electron microscope

B) Discovery of ribosomes

B) Invention of the light microscope

D) R. Virchow’s statement about the appearance of “each cell from the cell”

E) The emergence of the cell theory of T. Schwann and M. Schleiden

E) The first use of the term “cell” by R. Hooke

B13. Establish a correspondence between cell organelles and their functions

A) located on the granular ER

B) protein synthesis

B) photosynthesis 1) ribosomes

D) consist of two subunits 2) chloroplasts

D) consist of grana with thylakoids

E) form a polysome

C1. Find errors in the given text, correct them, indicate the numbers of the sentences in which they are made, write down these sentences without errors. 1. All living organisms - animals, plants, fungi, bacteria, viruses - consist of cells.

2. All cells have a plasma membrane.

3. Outside the membrane, the cells of living organisms have a rigid cell wall.

4. All cells have a nucleus.

5. The cell nucleus contains the genetic material of the cell - DNA molecules.

Give a complete detailed answer to the question

C2. Prove that the cell is an open system.

C3. What is the role of biological membranes in a cell?

C4. How do ribosomes form in eukaryotic cells?

C5. What similarities between mitochondria and prokaryotes allowed us to put forward the symbiotic theory of the origin of the eukaryotic cell?

C6. What is the structure and function of the core shell?

C7. What features of chromosomes ensure the transmission of hereditary information?

Answers to level A questions

Answers to Level B assignments

AT 10 O'CLOCK. 1 A B D

AT 11. 1 C D E E

AT 12. B E D G A B

On the right is the largest helix of human DNA, built from people on the beach in Varna (Bulgaria), included in the Guinness Book of Records on April 23, 2016

Deoxyribonucleic acid. General information

DNA (deoxyribonucleic acid) is a kind of blueprint for life, a complex code that contains data on hereditary information. This complex macromolecule is capable of storing and transmitting hereditary genetic information from generation to generation. DNA determines such properties of any living organism as heredity and variability. The information encoded in it sets the entire development program of any living organism. Genetically determined factors predetermine the entire course of life of both a person and any other organism. Artificial or natural influences of the external environment can only slightly affect the overall expression of individual genetic traits or affect the development of programmed processes.

Deoxyribonucleic acid(DNA) is a macromolecule (one of the three main ones, the other two are RNA and proteins) that ensures storage, transmission from generation to generation and implementation of the genetic program for the development and functioning of living organisms. DNA contains information about the structure of various types of RNA and proteins.

In eukaryotic cells (animals, plants and fungi), DNA is found in the cell nucleus as part of chromosomes, as well as in some cellular organelles (mitochondria and plastids). In the cells of prokaryotic organisms (bacteria and archaea), a circular or linear DNA molecule, the so-called nucleoid, is attached from the inside to the cell membrane. In them and in lower eukaryotes (for example, yeast), small autonomous, predominantly circular DNA molecules called plasmids are also found.

From a chemical point of view, DNA is a long polymer molecule consisting of repeating blocks called nucleotides. Each nucleotide consists of a nitrogenous base, a sugar (deoxyribose) and a phosphate group. The bonds between nucleotides in the chain are formed by deoxyribose ( WITH) and phosphate ( F) groups (phosphodiester bonds).

Rice. 2. A nucleotide consists of a nitrogenous base, a sugar (deoxyribose) and a phosphate group

In the vast majority of cases (except for some viruses containing single-stranded DNA), the DNA macromolecule consists of two chains oriented with nitrogenous bases towards each other. This double-stranded molecule is twisted along a helix.

There are four types of nitrogenous bases found in DNA (adenine, guanine, thymine and cytosine). The nitrogenous bases of one of the chains are connected to the nitrogenous bases of the other chain by hydrogen bonds according to the principle of complementarity: adenine combines only with thymine ( A-T), guanine - only with cytosine ( G-C). It is these pairs that make up the “rungs” of the DNA spiral “staircase” (see: Fig. 2, 3 and 4).

Rice. 2. Nitrogenous bases

The sequence of nucleotides allows you to “encode” information about various types of RNA, the most important of which are messenger or template (mRNA), ribosomal (rRNA) and transport (tRNA). All these types of RNA are synthesized on a DNA template by copying a DNA sequence into an RNA sequence synthesized during transcription, and take part in protein biosynthesis (the translation process). In addition to coding sequences, cell DNA contains sequences that perform regulatory and structural functions.

Rice. 3. DNA replication

The arrangement of basic combinations of DNA chemical compounds and the quantitative relationships between these combinations ensure the coding of hereditary information.

Education new DNA (replication)

1. Replication process: unwinding of the DNA double helix - synthesis of complementary strands by DNA polymerase - formation of two DNA molecules from one.
2. The double helix "unzips" into two branches when enzymes break the bond between the base pairs of chemical compounds.
3. Each branch is an element of new DNA. New base pairs are connected in the same sequence as in the parent branch.

Upon completion of duplication, two independent helices are formed, created from chemical compounds of the parent DNA and having the same genetic code. In this way, DNA is able to pass information from cell to cell.

More detailed information:

STRUCTURE OF NUCLEIC ACIDS

Rice. 4 . Nitrogen bases: adenine, guanine, cytosine, thymine

Deoxyribonucleic acid(DNA) refers to nucleic acids. Nucleic acids are a class of irregular biopolymers whose monomers are nucleotides.

NUCLEOTIDES consist of nitrogenous base, connected to a five-carbon carbohydrate (pentose) - deoxyribose(in case of DNA) or ribose(in the case of RNA), which combines with a phosphoric acid residue (H 2 PO 3 -).

Nitrogenous bases There are two types: pyrimidine bases - uracil (only in RNA), cytosine and thymine, purine bases - adenine and guanine.

Rice. 5. Structure of nucleotides (left), location of the nucleotide in DNA (bottom) and types of nitrogenous bases (right): pyrimidine and purine

The carbon atoms in the pentose molecule are numbered from 1 to 5. The phosphate combines with the third and fifth carbon atoms. This is how nucleinotides are combined into a nucleic acid chain. Thus, we can distinguish the 3' and 5' ends of the DNA strand:

Rice. 6. Isolation of the 3' and 5' ends of the DNA chain

Two strands of DNA form double helix. These chains in the spiral are oriented in opposite directions. In different strands of DNA, nitrogenous bases are connected to each other by hydrogen bonds. Adenine always pairs with thymine, and cytosine always pairs with guanine. It is called complementarity rule.

Complementarity rule:

A-T G-C

For example, if we are given a DNA strand with the sequence

3’- ATGTCCTAGCTGCTCG - 5’,

then the second chain will be complementary to it and directed in the opposite direction - from the 5’ end to the 3’ end:

5'- TACAGGATCGACGAGC- 3'.

Rice. 7. Direction of the chains of the DNA molecule and the connection of nitrogenous bases using hydrogen bonds

DNA REPLICATION

DNA replication is the process of doubling a DNA molecule through template synthesis. In most cases of natural DNA replicationprimerfor DNA synthesis is short fragment (recreated). Such a ribonucleotide primer is created by the enzyme primase (DNA primase in prokaryotes, DNA polymerase in eukaryotes), and is subsequently replaced by deoxyribonucleotide polymerase, which normally performs repair functions (correcting chemical damage and breaks in the DNA molecule).

Replication occurs according to a semi-conservative mechanism. This means that the double helix of DNA unwinds and a new chain is built on each of its chains according to the principle of complementarity. The daughter DNA molecule thus contains one strand from the parent molecule and one newly synthesized one. Replication occurs in the direction from the 3' to the 5' end of the mother strand.

Rice. 8. Replication (doubling) of a DNA molecule

DNA synthesis- this is not as complicated a process as it might seem at first glance. If you think about it, first you need to figure out what synthesis is. This is the process of combining something into one whole. The formation of a new DNA molecule occurs in several stages:

1) DNA topoisomerase, located in front of the replication fork, cuts the DNA in order to facilitate its unwinding and unwinding.
2) DNA helicase, following topoisomerase, influences the process of “unbraiding” of the DNA helix.
3) DNA-binding proteins bind DNA strands and also stabilize them, preventing them from sticking to each other.
4) DNA polymerase δ(delta) , coordinated with the speed of movement of the replication fork, carries out synthesisleadingchains subsidiary DNA in the 5"→3" direction on the matrix maternal DNA strands in the direction from its 3" end to the 5" end (speed up to 100 nucleotide pairs per second). These events at this maternal DNA strands are limited.

Rice. 9. Schematic representation of the DNA replication process: (1) Lagging strand (lagging strand), (2) Leading strand (leading strand), (3) DNA polymerase α (Polα), (4) DNA ligase, (5) RNA -primer, (6) Primase, (7) Okazaki fragment, (8) DNA polymerase δ (Polδ), (9) Helicase, (10) Single-stranded DNA-binding proteins, (11) Topoisomerase.

The synthesis of the lagging strand of daughter DNA is described below (see. Scheme replication fork and functions of replication enzymes)

For more information about DNA replication, see

5) Immediately after the other strand of the mother molecule is unraveled and stabilized, it is attached to itDNA polymerase α(alpha)and in the 5"→3" direction it synthesizes a primer (RNA primer) - an RNA sequence on a DNA template with a length of 10 to 200 nucleotides. After this the enzymeremoved from the DNA strand.

Instead of DNA polymerasesα is attached to the 3" end of the primer DNA polymeraseε .

6) DNA polymeraseε (epsilon) seems to continue to extend the primer, but inserts it as a substratedeoxyribonucleotides(in the amount of 150-200 nucleotides). As a result, a single thread is formed from two parts -RNA(i.e. primer) and DNA. DNA polymerase εruns until it encounters the previous primerfragment of Okazaki(synthesized a little earlier). After this, this enzyme is removed from the chain.

7) DNA polymerase β(beta) stands insteadDNA polymerase ε,moves in the same direction (5"→3") and removes the primer ribonucleotides while simultaneously inserting deoxyribonucleotides in their place. The enzyme works until the primer is completely removed, i.e. until a deoxyribonucleotide (an even earlier synthesizedDNA polymerase ε). The enzyme is not able to connect the result of its work with the DNA in front, so it goes off the chain.

As a result, a fragment of daughter DNA “lies” on the matrix of the mother strand. It is calledfragment of Okazaki.

8) DNA ligase crosslinks two adjacent fragments of Okazaki , i.e. 5" end of the segment synthesizedDNA polymerase ε,and 3"-end chain built-inDNA polymeraseβ .

STRUCTURE OF RNA

Ribonucleic acid(RNA) is one of the three main macromolecules (the other two are DNA and proteins) that are found in the cells of all living organisms.

Just like DNA, RNA consists of a long chain in which each link is called nucleotide. Each nucleotide consists of a nitrogenous base, a ribose sugar, and a phosphate group. However, unlike DNA, RNA usually has one strand rather than two. The pentose in RNA is ribose, not deoxyribose (ribose has an additional hydroxyl group on the second carbohydrate atom). Finally, DNA differs from RNA in the composition of nitrogenous bases: instead of thymine ( T) RNA contains uracil ( U) , which is also complementary to adenine.

The sequence of nucleotides allows RNA to encode genetic information. All cellular organisms use RNA (mRNA) to program protein synthesis.

Cellular RNA is produced through a process called transcription , that is, the synthesis of RNA on a DNA matrix, carried out by special enzymes - RNA polymerases.

Messenger RNAs (mRNAs) then take part in a process called broadcast, those. protein synthesis on an mRNA matrix with the participation of ribosomes. Other RNAs undergo chemical modifications after transcription, and after the formation of secondary and tertiary structures, they perform functions depending on the type of RNA.

Rice. 10. The difference between DNA and RNA in the nitrogenous base: instead of thymine (T), RNA contains uracil (U), which is also complementary to adenine.

TRANSCRIPTION

This is the process of RNA synthesis on a DNA template. DNA unwinds at one of the sites. One of the strands contains information that needs to be copied onto an RNA molecule - this strand is called the coding strand. The second strand of DNA, complementary to the coding one, is called the template. During transcription, a complementary RNA chain is synthesized on the template strand in the 3’ - 5’ direction (along the DNA strand). This creates an RNA copy of the coding strand.

Rice. 11. Schematic representation of the transcription

For example, if we are given the sequence of the coding chain

3’- ATGTCCTAGCTGCTCG - 5’,

then, according to the complementarity rule, the matrix chain will carry the sequence

5’- TACAGGATCGACGAGC- 3’,

and the RNA synthesized from it is the sequence

BROADCAST

Let's consider the mechanism protein synthesis on the RNA matrix, as well as the genetic code and its properties. Also, for clarity, at the link below, we recommend watching a short video about the processes of transcription and translation occurring in a living cell:

Rice. 12. Protein synthesis process: DNA codes for RNA, RNA codes for protein

GENETIC CODE

Genetic code- a method of encoding the amino acid sequence of proteins using a sequence of nucleotides. Each amino acid is encoded by a sequence of three nucleotides - a codon or triplet.

Genetic code common to most pro- and eukaryotes. The table shows all 64 codons and the corresponding amino acids. The base order is from the 5" to the 3" end of the mRNA.

Table 1. Standard genetic code

1st the basis tion	2nd base								3rd the basis tion
	U		C		A		G
U	U U U	(Phe/F)	U C U	(Ser/S)	U A U	(Tyr/Y)	U G U	(Cys/C)	U
	U U C		U C C		U A C		U G C		C
	U U A	(Leu/L)	U C A		U A A	Stop codon**	U G A	Stop codon**	A
	U U G		U C G		U A G	Stop codon**	U G G	(Trp/W)	G
C	C U U		C C U	(Pro/P)	C A U	(His/H)	C G U	(Arg/R)	U
	C U C		C C C		C A C		C G C		C
	C U A		C C A		C A A	(Gln/Q)	C GA		A
	C U G		C C G		C A G		C G G		G
A	A U U	(Ile/I)	A C U	(Thr/T)	A A U	(Asn/N)	A G U	(Ser/S)	U
	A U C		A C C		A A C		A G C		C
	A U A		A C A		A A A	(Lys/K)	A G A		A
	A U G	(Met/M)	A C G		A A G		A G G		G
G	G U U	(Val/V)	G C U	(Ala/A)	G A U	(Asp/D)	G G U	(Gly/G)	U
	G U C		G C C		G A C		G G C		C
	G U A		G C A		G A A	(Glu/E)	G G A		A
	G U G		G C G		G A G		G G G		G

Among the triplets, there are 4 special sequences that serve as “punctuation marks”:

• *Triplet AUG, also encoding methionine, is called start codon. The synthesis of a protein molecule begins with this codon. Thus, during protein synthesis, the first amino acid in the sequence will always be methionine.

• **Triplets UAA, UAG And U.G.A. are called stop codons and do not code for a single amino acid. At these sequences, protein synthesis stops.

Properties of the genetic code

1. Triplety. Each amino acid is encoded by a sequence of three nucleotides - a triplet or codon.

2. Continuity. There are no additional nucleotides between the triplets; the information is read continuously.

3. Non-overlapping. One nucleotide cannot be included in two triplets at the same time.

4. Unambiguity. One codon can code for only one amino acid.

5. Degeneracy. One amino acid can be encoded by several different codons.

6. Versatility. The genetic code is the same for all living organisms.

Example. We are given the sequence of the coding chain:

3’- CCGATTGCACGTCGATCGTATA- 5’.

The matrix chain will have the sequence:

5’- GGCTAACGTGCAGCTAGCATAT- 3’.

Now we “synthesize” information RNA from this chain:

3’- CCGAUUGCACGUCGAUCGUAUA- 5’.

Protein synthesis proceeds in the direction 5’ → 3’, therefore, we need to reverse the sequence to “read” the genetic code:

5’- AUAUGCUAGCUGCACGUUAGCC- 3’.

Now let's find the start codon AUG:

5’- AU AUG CUAGCUGCACGUUAGCC- 3’.

Let's divide the sequence into triplets:

sounds like this: information is transferred from DNA to RNA (transcription), from RNA to protein (translation). DNA can also be duplicated by replication, and the process of reverse transcription is also possible, when DNA is synthesized from an RNA template, but this process is mainly characteristic of viruses.

Rice. 13. Central Dogma of Molecular Biology

GENOME: GENES and CHROMOSOMES

(general concepts)

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

The term “genome” was proposed by G. Winkler in 1920 to describe the set of genes contained in the haploid set of chromosomes of organisms of one biological species. The original meaning of this term indicated that the concept of a genome, in contrast to a genotype, is a genetic characteristic of the species as a whole, and not of an individual. With the development of molecular genetics, the meaning of this term has changed. It is known that DNA, which is the carrier of genetic information in most organisms and, therefore, forms the basis of the genome, includes not only genes in the modern sense of the word. Most of the DNA of eukaryotic cells is represented by non-coding (“redundant”) nucleotide sequences that do not contain information about proteins and nucleic acids. Thus, the main part of the genome of any organism is the entire DNA of its haploid set of chromosomes.

Genes are sections of DNA molecules that encode polypeptides and RNA molecules

Over the last century, our understanding of genes has changed significantly. Previously, a genome was a region of a chromosome that encodes or defines one characteristic or phenotypic(visible) property, such as eye color.

In 1940, George Beadle and Edward Tatham proposed a molecular definition of the gene. Scientists processed fungal spores Neurospora crassa X-rays and other agents that cause changes in the DNA sequence ( mutations), and discovered mutant strains of the fungus that had lost some specific enzymes, which in some cases led to disruption of the entire metabolic pathway. Beadle and Tatem concluded that a gene is a piece of genetic material that specifies or codes for a single enzyme. This is how the hypothesis appeared "one gene - one enzyme". This concept was later expanded to define "one gene - one polypeptide", since many genes encode proteins that are not enzymes, and the polypeptide may be a subunit of a complex protein complex.

In Fig. Figure 14 shows a diagram of how triplets of nucleotides in DNA determine a polypeptide - the amino acid sequence of a protein through the mediation of mRNA. One of the DNA chains plays the role of a template for the synthesis of mRNA, the nucleotide triplets (codons) of which are complementary to the DNA triplets. In some bacteria and many eukaryotes, coding sequences are interrupted by non-coding regions (called introns).

Modern biochemical determination of the gene even more specific. Genes are all sections of DNA that encode the primary sequence of end products, which include polypeptides or RNA that have a structural or catalytic function.

Along with genes, DNA also contains other sequences that perform exclusively a regulatory function. Regulatory sequences may mark the beginning or end of genes, influence transcription, or indicate the site of initiation of replication or recombination. Some genes can be expressed in different ways, with the same DNA region serving as a template for the formation of different products.

We can roughly calculate minimum gene size, encoding the middle protein. Each amino acid in a polypeptide chain is encoded by a sequence of three nucleotides; the sequences of these triplets (codons) correspond to the chain of amino acids in the polypeptide that is encoded by this gene. A polypeptide chain of 350 amino acid residues (medium length chain) corresponds to a sequence of 1050 bp. ( base pairs). However, many eukaryotic genes and some prokaryotic genes are interrupted by DNA segments that do not carry protein information, and therefore turn out to be much longer than a simple calculation shows.

How many genes are on one chromosome?

Rice. 15. View of chromosomes in prokaryotic (left) and eukaryotic cells. Histones are a large class of nuclear proteins that perform two main functions: they participate in the packaging of DNA strands in the nucleus and in the epigenetic regulation of nuclear processes such as transcription, replication and repair.

As is known, bacterial cells have a chromosome in the form of a DNA strand arranged in a compact structure - a nucleoid. Prokaryotic chromosome Escherichia coli, whose genome has been completely deciphered, is a circular DNA molecule (in fact, it is not a perfect circle, but rather a loop without a beginning or end), consisting of 4,639,675 bp. This sequence contains approximately 4,300 protein genes and another 157 genes for stable RNA molecules. IN human genome approximately 3.1 billion base pairs corresponding to nearly 29,000 genes located on 24 different chromosomes.

Prokaryotes (Bacteria).

Bacterium E. coli has one double-stranded circular DNA molecule. It consists of 4,639,675 bp. and reaches a length of approximately 1.7 mm, which exceeds the length of the cell itself E. coli approximately 850 times. In addition to the large circular chromosome as part of the nucleoid, many bacteria contain one or several small circular DNA molecules that are freely located in the cytosol. These extrachromosomal elements are called plasmids(Fig. 16).

Most plasmids consist of only a few thousand base pairs, some contain more than 10,000 bp. They carry genetic information and replicate to form daughter plasmids, which enter the daughter cells during the division of the parent cell. Plasmids are found not only in bacteria, but also in yeast and other fungi. In many cases, plasmids provide no benefit to the host cells and their sole purpose is to reproduce independently. However, some plasmids carry genes beneficial to the host. For example, genes contained in plasmids can make bacterial cells resistant to antibacterial agents. Plasmids carrying the β-lactamase gene provide resistance to β-lactam antibiotics such as penicillin and amoxicillin. Plasmids can pass from cells that are resistant to antibiotics to other cells of the same or a different species of bacteria, causing those cells to also become resistant. Intensive use of antibiotics is a powerful selective factor that promotes the spread of plasmids encoding antibiotic resistance (as well as transposons that encode similar genes) among pathogenic bacteria, leading to the emergence of bacterial strains with resistance to multiple antibiotics. Doctors are beginning to understand the dangers of widespread use of antibiotics and prescribe them only in cases of urgent need. For similar reasons, the widespread use of antibiotics to treat farm animals is limited.

See also: Ravin N.V., Shestakov S.V. Genome of prokaryotes // Vavilov Journal of Genetics and Breeding, 2013. T. 17. No. 4/2. pp. 972-984.

Eukaryotes.

Table 2. DNA, genes and chromosomes of some organisms

	Shared DNA p.n.	Number of chromosomes*	Approximate number of genes
Escherichia coli(bacterium)	4 639 675		4 435
Saccharomyces cerevisiae(yeast)	12 080 000	16**	5 860
Caenorhabditis elegans(nematode)	90 269 800	12***	23 000
Arabidopsis thaliana(plant)	119 186 200		33 000
Drosophila melanogaster(fruit fly)	120 367 260		20 000
Oryza sativa(rice)	480 000 000		57 000
Mus musculus(mouse)	2 634 266 500		27 000
Homo sapiens(Human)	3 070 128 600		29 000

Note. Information is constantly updated; For more up-to-date information, refer to individual genomics project websites

* For all eukaryotes, except yeast, the diploid set of chromosomes is given. Diploid kit chromosomes (from the Greek diploos - double and eidos - species) - a double set of chromosomes (2n), each of which has a homologous one.
**Haploid set. Wild yeast strains typically have eight (octaploid) or more sets of these chromosomes.
***For females with two X chromosomes. Males have an X chromosome, but no Y, i.e. only 11 chromosomes.

Yeast, one of the smallest eukaryotes, has 2.6 times more DNA than E. coli(Table 2). Fruit fly cells Drosophila, a classic subject of genetic research, contain 35 times more DNA, and human cells contain approximately 700 times more DNA than E. coli. Many plants and amphibians contain even more DNA. The genetic material of eukaryotic cells is organized in the form of chromosomes. Diploid set of chromosomes (2 n) depends on the type of organism (Table 2).

For example, in a human somatic cell there are 46 chromosomes ( rice. 17). Each chromosome of a eukaryotic cell, as shown in Fig. 17, A, contains one very large double-stranded DNA molecule. Twenty-four human chromosomes (22 paired chromosomes and two sex chromosomes X and Y) vary in length by more than 25 times. Each eukaryotic chromosome contains a specific set of genes.

Rice. 17. Chromosomes of eukaryotes.A- a pair of linked and condensed sister chromatids from the human chromosome. In this form, eukaryotic chromosomes remain after replication and in metaphase during mitosis. b- a complete set of chromosomes from a leukocyte of one of the authors of the book. Each normal human somatic cell contains 46 chromosomes.

If you connect the DNA molecules of the human genome (22 chromosomes and chromosomes X and Y or X and X), you get a sequence about one meter long. Note: In all mammals and other heterogametic male organisms, females have two X chromosomes (XX) and males have one X chromosome and one Y chromosome (XY).

Most human cells, so the total DNA length of such cells is about 2 m. An adult human has approximately 10 14 cells, so the total length of all DNA molecules is 2・10 11 km. For comparison, the circumference of the Earth is 4・10 4 km, and the distance from the Earth to the Sun is 1.5・10 8 km. This is how amazingly compact DNA is packed in our cells!

In eukaryotic cells there are other organelles containing DNA - mitochondria and chloroplasts. Many hypotheses have been put forward regarding the origin of mitochondrial and chloroplast DNA. The generally accepted point of view today is that they represent the rudiments of the chromosomes of ancient bacteria, which penetrated the cytoplasm of the host cells and became the precursors of these organelles. Mitochondrial DNA encodes mitochondrial tRNAs and rRNAs, as well as several mitochondrial proteins. More than 95% of mitochondrial proteins are encoded by nuclear DNA.

STRUCTURE OF GENES

Let's consider the structure of the gene in prokaryotes and eukaryotes, their similarities and differences. Despite the fact that a gene is a section of DNA that encodes only one protein or RNA, in addition to the immediate coding part, it also includes regulatory and other structural elements that have different structures in prokaryotes and eukaryotes.

Coding sequence- the main structural and functional unit of the gene, it is in it that the triplets of nucleotides encoding are locatedamino acid sequence. It begins with a start codon and ends with a stop codon.

Before and after the coding sequence there are untranslated 5' and 3' sequences. They perform regulatory and auxiliary functions, for example, ensuring the landing of the ribosome on mRNA.

Untranslated and coding sequences make up the transcription unit - the transcribed section of DNA, that is, the section of DNA from which mRNA synthesis occurs.

Terminator- a non-transcribed section of DNA at the end of a gene where RNA synthesis stops.

At the beginning of the gene is regulatory region, which includes promoter And operator.

Promoter- the sequence to which the polymerase binds during transcription initiation. Operator- this is an area that special proteins can bind to - repressors, which can reduce the activity of RNA synthesis from this gene - in other words, reduce it expression.

Gene structure in prokaryotes

The general plan of gene structure in prokaryotes and eukaryotes is no different - both contain a regulatory region with a promoter and operator, a transcription unit with coding and untranslated sequences, and a terminator. However, the organization of genes in prokaryotes and eukaryotes is different.

Rice. 18. Scheme of gene structure in prokaryotes (bacteria) -the image is enlarged

At the beginning and end of the operon there are common regulatory regions for several structural genes. From the transcribed region of the operon, one mRNA molecule is read, which contains several coding sequences, each of which has its own start and stop codon. From each of these areas withone protein is synthesized. Thus, Several protein molecules are synthesized from one mRNA molecule.

Prokaryotes are characterized by the combination of several genes into a single functional unit - operon. The operation of the operon can be regulated by other genes, which can be noticeably distant from the operon itself - regulators. The protein translated from this gene is called repressor. It binds to the operator of the operon, regulating the expression of all genes contained in it at once.

Prokaryotes are also characterized by the phenomenon Transcription-translation interfaces.

Rice. 19 The phenomenon of coupling of transcription and translation in prokaryotes - the image is enlarged

Such coupling does not occur in eukaryotes due to the presence of a nuclear envelope that separates the cytoplasm, where translation occurs, from the genetic material on which transcription occurs. In prokaryotes, during RNA synthesis on a DNA template, a ribosome can immediately bind to the synthesized RNA molecule. Thus, translation begins even before transcription is completed. Moreover, several ribosomes can simultaneously bind to one RNA molecule, synthesizing several molecules of one protein at once.

Gene structure in eukaryotes

The genes and chromosomes of eukaryotes are very complexly organized

Many species of bacteria have only one chromosome, and in almost all cases there is one copy of each gene on each chromosome. Only a few genes, such as rRNA genes, are found in multiple copies. Genes and regulatory sequences make up virtually the entire prokaryotic genome. Moreover, almost every gene strictly corresponds to the amino acid sequence (or RNA sequence) it encodes (Fig. 14).

The structural and functional organization of eukaryotic genes is much more complex. The study of eukaryotic chromosomes, and later the sequencing of complete eukaryotic genome sequences, brought many surprises. Many, if not most, eukaryotic genes have an interesting feature: their nucleotide sequences contain one or more DNA sections that do not encode the amino acid sequence of the polypeptide product. Such untranslated insertions disrupt the direct correspondence between the nucleotide sequence of the gene and the amino acid sequence of the encoded polypeptide. These untranslated segments within genes are called introns, or built-in sequences, and the coding segments are exons. In prokaryotes, only a few genes contain introns.

So, in eukaryotes, the combination of genes into operons practically does not occur, and the coding sequence of a eukaryotic gene is most often divided into translated regions - exons, and untranslated sections - introns.

In most cases, the function of introns is not established. In general, only about 1.5% of human DNA is “coding,” that is, it carries information about proteins or RNA. However, taking into account large introns, it turns out that human DNA is 30% genes. Because genes make up a relatively small proportion of the human genome, a significant portion of DNA remains unaccounted for.

Rice. 16. Scheme of gene structure in eukaryotes - the image is enlarged

From each gene, immature or pre-RNA is first synthesized, which contains both introns and exons.

After this, the splicing process takes place, as a result of which the intronic regions are excised, and a mature mRNA is formed, from which protein can be synthesized.

Rice. 20. Alternative splicing process - the image is enlarged

This organization of genes allows, for example, when different forms of a protein can be synthesized from one gene, due to the fact that during splicing exons can be stitched together in different sequences.

Rice. 21. Differences in the structure of genes of prokaryotes and eukaryotes - the image is enlarged

MUTATIONS AND MUTAGENESIS

Mutation is called a persistent change in the genotype, that is, a change in the nucleotide sequence.

The process that leads to mutations is called mutagenesis, and the body All whose cells carry the same mutation - mutant.

Mutation theory was first formulated by Hugo de Vries in 1903. Its modern version includes the following provisions:

1. Mutations occur suddenly, spasmodically.

2. Mutations are passed on from generation to generation.

3. Mutations can be beneficial, harmful or neutral, dominant or recessive.

4. The probability of detecting mutations depends on the number of individuals studied.

5. Similar mutations can occur repeatedly.

6. Mutations are not directed.

Mutations can occur under the influence of various factors. There are mutations that arise under the influence of mutagenic impacts: physical (for example, ultraviolet or radiation), chemical (for example, colchicine or reactive oxygen species) and biological (for example, viruses). Mutations can also be caused replication errors.

Depending on the conditions under which mutations appear, mutations are divided into spontaneous- that is, mutations that arose under normal conditions, and induced- that is, mutations that arose under special conditions.

Mutations can occur not only in nuclear DNA, but also, for example, in mitochondrial or plastid DNA. Accordingly, we can distinguish nuclear And cytoplasmic mutations.

As a result of mutations, new alleles can often appear. If a mutant allele suppresses the action of a normal one, the mutation is called dominant. If a normal allele suppresses a mutant one, this mutation is called recessive. Most mutations that lead to the emergence of new alleles are recessive.

Mutations are distinguished by effect adaptive leading to increased adaptability of the organism to the environment, neutral, which do not affect survival, harmful, reducing the adaptability of organisms to environmental conditions and lethal, leading to the death of the organism in the early stages of development.

According to the consequences, mutations leading to loss of protein function, mutations leading to emergence protein has a new function, as well as mutations that change gene dosage, and, accordingly, the dose of protein synthesized from it.

A mutation can occur in any cell of the body. If a mutation occurs in a germ cell, it is called germinal(germinal or generative). Such mutations do not appear in the organism in which they appeared, but lead to the appearance of mutants in the offspring and are inherited, so they are important for genetics and evolution. If a mutation occurs in any other cell, it is called somatic. Such a mutation can manifest itself to one degree or another in the organism in which it arose, for example, leading to the formation of cancerous tumors. However, such a mutation is not inherited and does not affect descendants.

Mutations can affect regions of the genome of different sizes. Highlight genetic, chromosomal And genomic mutations.

Gene mutations

Mutations that occur on a scale smaller than one gene are called genetic, or point (point). Such mutations lead to changes in one or several nucleotides in the sequence. Among gene mutations there arereplacements, leading to the replacement of one nucleotide with another,deletions, leading to the loss of one of the nucleotides,insertions, leading to the addition of an extra nucleotide to the sequence.

Rice. 23. Gene (point) mutations

According to the mechanism of action on the protein, gene mutations are divided into:synonymous, which (as a result of the degeneracy of the genetic code) do not lead to a change in the amino acid composition of the protein product,missense mutations, which lead to the replacement of one amino acid with another and can affect the structure of the synthesized protein, although they are often insignificant,nonsense mutations, leading to the replacement of the coding codon with a stop codon,mutations leading to splicing disorder:

Rice. 24. Mutation patterns

Also, according to the mechanism of action on the protein, mutations are distinguished that lead to frame shift reading, such as insertions and deletions. Such mutations, like nonsense mutations, although they occur at one point in the gene, often affect the entire structure of the protein, which can lead to a complete change in its structure.

Rice. 29. Chromosome before and after duplication

Genomic mutations

Finally, genomic mutations affect the entire genome, that is, the number of chromosomes changes. There are polyploidies - an increase in the ploidy of the cell, and aneuploidies, that is, a change in the number of chromosomes, for example, trisomy (the presence of an additional homologue on one of the chromosomes) and monosomy (the absence of a homolog on a chromosome).

Video on DNA

DNA REPLICATION, RNA CODING, PROTEIN SYNTHESIS

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 circulation 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 the missing terms from the proposed list into the text “Nutrition in the sheet”, 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 by 5-9 years, and is caught at 3 years (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. Cough occurs with strong inhalation.

6. Gor-tan moves into two large bronchi.

Explanation: sentence-3 - the epiglottis (supraglottic cartilage) closes the entrance to the larynx, and not to 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: oat soamtic cells 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 analytical cross (with a recessive homozygote):

P2: AaBv x aavv

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