Question 1. What is dissimilation? List its stages.
Dissimilation, or energy metabolism, is a set of reactions of cleavage of high-molecular compounds, which are accompanied by the release and storage of energy. Dissimilation in aerobic (oxygen-breathing) organisms occurs in three stages:
preparatory - the breakdown of high molecular weight compounds to low molecular weight ones without storing energy;
oxygen-free - partial oxygen-free breakdown of compounds, energy is stored in the form of ATP; oxygen - the final breakdown of organic substances to carbon dioxide and water, energy is also stored in the form of ATP.
Dissimilation in anaerobic (not using oxygen) organisms occurs in two stages: preparatory and oxygen-free. IN in this case Organic substances are not completely broken down and much less energy is stored.
Question 2. What is the role of ATP in cell metabolism?
Adenosine triphosphoric acid (ATP) consists of a nitrogenous base - adenine, a sugar - ribose and three residues phosphoric acid. The ATP molecule is very unstable and is capable of splitting off one or two phosphate molecules, releasing large quantity energy spent to ensure all vital functions of the cell (biosynthesis, transmembrane transfer, movement, formation of an electrical impulse, etc.). The bonds in the ATP molecule are called macroergic.
The cleavage of the terminal phosphate from the ATP molecule is accompanied by the release of 40 kJ of energy.). In this case, ATP is converted into ADP. If the second phosphoric acid residue is eliminated, ADP is converted to AMP. All processes in living organisms that require energy are accompanied by the conversion of ATP molecules into ADP (or even AMP).
ATP synthesis occurs in mitochondria.
Question 3. What cell structures carry out ATP synthesis?
In eukaryotic cells, the synthesis of the bulk of ATP from ADP and phosphoric acid occurs in mitochondria and is accompanied by the absorption (storage) of energy. In plastids, ATP is formed as an intermediate product of the light stage of photosynthesis.
Question 4. Tell us about energy metabolism in a cell using the breakdown of glucose as an example.
Energy metabolism is usually divided into three stages. The first stage is Preparatory, also called digestion. It is carried out mainly outside the cells under the action of enzymes secreted into the cavity of the digestive tract. At this stage, large polymer molecules break down into monomers: proteins into amino acids, polysaccharides into simple sugars, fats into fatty acid and glycerin. At the same time, it stands out a small amount of energy that is dissipated in the form of heat.
Oxygen-free. As a result of glycolysis, one molecule of glucose is broken down into two molecules of pyruvic acid:
C 6 H 12 O 6<----->2C 3 H 4 0 3 .
The breakdown of one glucose molecule is accompanied by the formation of two ATP molecules. In this case, 60% of the released energy is converted into heat, and 40% is stored in the form of ATP. The breakdown of one glucose molecule produces 2 ATP molecules. Then, in anaerobic organisms, fermentation occurs - alcoholic (C 2 HC 5 OH - ethyl alcohol) or lactic acid (C 3 H 4 0 3 - lactic acid). In aerobic organisms, the third stage of energy metabolism begins.
Oxygen. This stage of catabolism requires the presence of molecular oxygen and is called respiration. The development of cellular respiration in aerobic microorganisms and in eukaryotic cells became possible only after molecular oxygen appeared in the Earth’s atmosphere as a result of photosynthesis. The addition of an oxygen step to the catalytic process provides cells with a powerful and efficient way to extract nutrients and energy from molecules.
Reactions of oxygen splitting, or oxidative catabolism, occur in special cell organelles - mitochondria, where molecules of pyruvic acid enter. After a number of terminations, the final products are formed - CO 2 and H 2 O, which then diffuse out of the cell. The overall equation for aerobic respiration looks like this:
C 6 H 12 O 6 + 6O 2 + 36H 3 PO 4 + 36ADP<----->6CO 2 + 6H 2 O + 36ATP.
Thus, the oxidation of two molecules of lactic acid produces 36 molecules of ATP. In total, during the second and third stages of energy metabolism, the breakdown of one glucose molecule produces 38 ATP molecules. Consequently, aerobic respiration plays the main role in providing the cell with energy.
Any property of living things, and any manifestation of life is associated with certain chemical reactions in the cell. These reactions occur either with the expenditure or with the release of energy. The entire set of processes of transformation of substances in a cell, as well as in the body, is called metabolism.
During its life, a cell maintains the constancy of its internal environment, called homeostasis. To do this, it synthesizes substances in accordance with its genetic information.
Rice. 1. Metabolic scheme.
This part of metabolism, during which high-molecular compounds characteristic of a given cell are created, is called plastic metabolism (assimilation, anabolism).
Anabolic reactions include:
These reactions are only possible with the expenditure of energy. If external (light) energy is spent for photosynthesis, then for the rest - the resources of the cell.
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The amount of energy spent on assimilation is greater than what is stored in chemical bonds, since part of it is used to regulate the process.
The other side of metabolism and energy transformation in a cell is energy metabolism (dissimilation, catabolism).
Catabolic reactions are accompanied by the release of energy.
This process includes:
Rice. 2. Catabolic processes in the cell.
All processes in a cell are closely related to each other, as well as to processes in other cells and organs. Transformations of organic substances depend on the availability inorganic acids, macro- and microelements.
The processes of catabolism and anabolism occur simultaneously in the cell and are two opposing components of metabolism.
Metabolic processes are associated with certain cell structures:
Cells are not characterized by individual chemical processes, but the natural order in which they are carried out. Metabolism regulators are enzyme proteins that direct reactions and change their intensity.
Adenosine triphosphoric acid (ATP) plays a special role in metabolism. It is a compact chemical energy storage device used for fusion reactions.
Rice. 3. Scheme of the structure of ATP and its conversion to ADP.
Due to its instability, ATP forms molecules of ADP and AMP (di- and monophosphate) with the release of a large amount of energy for assimilation processes.
All living organisms exchange substances with the external environment. Biosynthesis processes are constantly carried out in cells. Thanks to enzymes simple substances Complex compounds are formed: proteins are synthesized from amino acids, complex carbohydrates are synthesized from monosaccharides, and nucleic acids are synthesized from nitrogenous bases. Various fats and oils are formed through chemical transformations of relatively simple substances. Chitin is the outer cover of arthropods, forming chitin - a complex polysaccharide (p. 7); in birds and mammals, the outer cover is a horny substance, the basis of which is the protein keratin. Ultimately, the composition of the large organic molecules synthesized is determined by the genotype. Synthesized substances are used during growth to construct cells and their organelles and to replace spent or destroyed molecules. Without exception, all interactions of biosynthesis occur with the absorption of energy.
Plastic exchange
Plastic metabolism, otherwise called biosynthesis or anabolism, this exchange occurs only in the cell. Plastic metabolism has three types: photosynthesis, chemosynthesis and protein biosynthesis. Photosynthesis is used by plants and only some bacteria (cyanobacteria). Such organisms are called autotrophs. Chemosynthesis is used by certain bacteria, including anaerobic ones. Such organisms are called chemotrophs. Animals and fungi are classified as heterotrophic creatures.
Photosynthesis
The process of photosynthesis occurs through a reaction that involves the formation of glucose and oxygen from carbon dioxide and water. Photosynthesis has two phases, light and dark. During the light phase, the process of photosynthesis occurs in the grana of the chloroplast, and in the dark phase, in the stroma of the chloroplast (see Appendix 7). Without solar energy, photosynthesis would not have its meaning, so this is important factor. During this process, six molecules of carbon dioxide and water are formed from six molecules of oxygen and one molecule of glucose. The process of photosynthesis occurs in chloroplasts; chlorophyll is found in organelles, thanks to which synthesis occurs.
6СО2 + 6Н2О → С6Н12О6 + 6О2
Chemosynthesis
Chemosynthesis is characteristic of bacteria such as sulfur, nitrifying and iron bacteria. Bacteria use the energy acquired through the process of oxidation of substances to reduce carbon dioxide to organic compounds.(see Appendix 8) Sulfur bacteria oxidize substances such as hydrogen sulfide, nitrifying bacteria oxidize ammonia, and iron bacteria oxidize ferric oxide.
Protein biosynthesis
Plastic metabolism is the synthesis of proteins by a cell. Exchange has two main processes: transcription and translation.
Transcription- This is the process of synthesizing messenger RNA using DNA according to the principle of complementarity. (see Appendix 9)
Transcription has three stages:
Primary transcript formation
Processing
Splicing
Broadcast- transfer of information about the structure of a protein from messenger RNA to the synthesized polypeptide. (see Appendix 10) This process is carried out in the cytoplasm on the ribosome. The broadcast takes place in four stages. At the first stage, amino acids are activated by a special enzyme - aminoacyl T-RNA synthetase. This process uses energy in the form of ATP. Minoacyl adenylate is then formed. This is followed by the process of adjacency of the activated amino acid to the transfer RNA, and AMP is released. Further, during the third stage, the formed complex binds to the ribosome. Amino acids are then incorporated into the protein structure in a specific sequence, after which the transfer RNA is released.
Energy metabolism
Energy metabolism is also called catabolism. Plastic and energy metabolism are very connected, because to carry out plastic metabolism (anabolism), energy is needed, which is obtained by the cell through catabolism. Using this process, the cell synthesizes the necessary nucleic acids, proteins, carbohydrates, etc. Energy metabolism is a process during which substances with a complex structure are broken down into simpler ones or oxidized, due to which the body acquires the energy required for existence. There are three stages of energy metabolism:
Preparatory stage
Anaerobic stage - glycolysis (without oxygen)
Aerobic stage - cellular respiration (with the participation of oxygen)
Preparatory stage
During this stage, polymers are converted into monomers, that is, compounds such as proteins, carbohydrates and lipoids are broken down into simpler ones. This process occurs outside the cell, in the organs of the digestive system. Oxygen is not required at this stage of energy metabolism. As a result of the reactions, protein breaks down into amino acids, complex carbohydrates into simple monosaccharides and lipids into glycerol and higher acids. This stage also occurs in the lysosomes of the cell.
Anaerobic stage
This stage is otherwise called fermentation or glycolysis. Formed in preparatory stage substances - glucose, amino acids, etc. - undergo subsequent enzymatic breakdown without the participation of oxygen. Carbohydrates are mainly fermented. During chemical reactions, used at this stage of catabolism, alcohols are formed, carbon dioxide, acetone, organic acids, in some cases hydrogen and other substances. Glycolysis is the process of breakdown of glucose under anaerobic conditions to pyruvic acid (PVA), then to lactic, acetic, butyric acids or ethyl alcohol, occurring in the cytoplasm of the cell. During oxygen-free fission, part of the released energy is dissipated in the form of heat, and part is stored in ATP molecules. A common reaction in animal and fungal cells is the release of pyruvic acid.
The main chemical reaction at this stage looks like that:
C6H12O6 = 2C3H4O3 + (4H) + 2ATP
As a result of this process, two ATP molecules are formed.
Aerobic stage
This stage takes place in mitochondria. (see Appendix 11) At this stage, substances are oxidized, due to which a certain amount of energy is released. Oxygen takes part in this same process. Oxygen is transported using red blood cells containing hemoglobin. The substances obtained in the previous stages are broken down by the cell to the simplest, that is, to carbon dioxide and water. Enzymes contained in lysosomes oxidize organic compounds in the cell. ADP - adenosine diphosphate - a substance that is also necessary for energy production due to cellular respiration. The basic chemical reaction at this stage looks like this:
2C3H6O3 + 6O2 + 36H3PO4 + 36ADP = 6CO2 + 42H2O + 36ATP
As a result of this process, 36 ATP molecules are formed.
You can see from this equation that a considerable amount of energy is released at this stage. In addition, at this stage, the reaction of complete oxidation of pyruvic acid can occur, as a result of which energy is also released, but in smaller quantities.
Consequently, with the complete breakdown of one glucose molecule, the cell can synthesize 38 ATP molecules (2 molecules during glycolysis and 36 molecules during the aerobic stage). (see Appendix 12)
The general equation for aerobic respiration can be written as follows:
C6H1206 + 602 + 38ADP + 38H3P04 > 6C02 + 6H20 + 38ATP.
Conclusion
A cell is a highly organized unit of life. The absorption, transformation, storage and use of substances and energy occurs through cells. It is in the cell that processes such as respiration, fermentation, photosynthesis, and duplication of genetic material occur. And such processes occur both in organisms that are simple in structure (unicellular) and in organisms that are complex in structure (multicellular). The life of all organisms depends on their cells.
Application
Annex 1
Appendix 2
Appendix 3
Appendix 4
Appendix 5
Appendix 6
Appendix 7
Appendix 8
Appendix 9
All living organisms on Earth are open systems capable of actively organizing the supply of energy and matter from the outside. Energy is necessary to carry out life important processes, but primarily for the chemical synthesis of substances used to build and restore cell and body structures. Living beings are capable of using only two types of energy: light(solar radiation energy) and chemical(energy of bonds of chemical compounds) - on this basis, organisms are divided into two groups - phototrophs and chemotrophs.
The main source of structural molecules is carbon. Depending on their carbon sources, living organisms are divided into two groups: autotrophs, which use an inorganic carbon source (carbon dioxide), and heterotrophs, which use organic carbon sources.
The process of consuming energy and matter is called food. Two methods of nutrition are known: holozoic - through the capture of food particles inside the body and holophytic - without capture, through the absorption of dissolved nutrients through the surface structures of the body. Nutrients that enter the body are involved in metabolic processes.
Metabolism is a set of interconnected and balanced processes that include a variety of chemical transformations in the body. Synthesis reactions carried out with energy consumption form the basis of anabolism (plastic metabolism or assimilation).
Splitting reactions accompanied by the release of energy form the basis catabolism(energy exchange or dissimilation).
1. The importance of ATP in metabolism
The energy released during the breakdown of organic substances is not immediately used by the cell, but is stored in the form of high-energy compounds, usually in the form of adenosine triphosphate (ATP). By its chemical nature, ATP is a mononucleotide and consists of the nitrogenous base adenine, the carbohydrate ribose and three phosphoric acid residues.
The energy released during ATP hydrolysis is used by the cell to perform all types of work. Significant amounts of energy are spent on biological synthesis. ATP is a universal source of cell energy. The supply of ATP in the cell is limited and is replenished due to the process of phosphorylation, which occurs at varying rates during respiration, fermentation and photosynthesis. ATP is renewed extremely quickly (in humans, the lifespan of one ATP molecule is less than 1 minute).
2. Energy metabolism in the cell. ATP synthesis
ATP synthesis occurs in the cells of all organisms during the process of phosphorylation, i.e. addition of inorganic phosphate to ADP. The energy for phosphorylation of ADP is generated during energy metabolism. Energy metabolism, or dissimilation, is a set of reactions of the breakdown of organic substances, accompanied by the release of energy. Depending on the habitat, dissimilation can occur in two or three stages.
In most living organisms - aerobes living in an oxygen environment - three stages are carried out during dissimilation: preparatory, oxygen-free, oxygen. In anaerobes living in an environment deprived of oxygen, or in aerobes with a lack of oxygen, dissimilation occurs only in the first two stages with the formation of intermediate organic compounds that are still rich in energy.
The first stage - preparatory - consists of the enzymatic breakdown of complex organic compounds into simpler ones (proteins into amino acids; polysaccharides into monosaccharides; nucleic acids to nucleotides). Intracellular breakdown of organic substances occurs under the action of hydrolytic enzymes of lysosomes. The energy released in this case is dissipated in the form of heat, and the resulting small organic molecules can undergo further breakdown and be used by the cell as “ construction material» for the synthesis of own organic compounds.
The second stage - incomplete oxidation - occurs directly in the cytoplasm of the cell, does not require the presence of oxygen and consists of further breakdown of organic substrates. The main source of energy in the cell is glucose. The oxygen-free, incomplete breakdown of glucose is called glycolysis.
The third stage - complete oxidation - occurs with the obligatory participation of oxygen. As a result, the glucose molecule is broken down into inorganic carbon dioxide, and the energy released in this case is partially spent on the synthesis of ATP.
3. Plastic exchange
Plastic metabolism, or assimilation, is a set of reactions that ensure the synthesis of complex organic compounds in the cell. Heterotrophic organisms build their own organic matter from organic food components. Heterotrophic assimilation is essentially reduced to the rearrangement of molecules.
Organic food substances (proteins, fats, carbohydrates) --> digestion --> Simple organic molecules (amino acids, fatty acids, monosaccharides) --> biological syntheses -->
Autotrophic organisms are capable of completely independently synthesizing organic substances from inorganic molecules consumed from external environment. In the process of autotrophic assimilation, the reactions of photo- and chemosynthesis, which ensure the formation of simple organic compounds, precede the biological syntheses of macromolecules:
Inorganic substances (carbon dioxide, water) --> photosynthesis, chemosynthesis --> Simple organic molecules (amino acids, fatty acids, monosaccharides) -----biological syntheses --> Body macromolecules (proteins, fats, carbohydrates)
4. Photosynthesis
Photosynthesis is the synthesis of organic compounds from inorganic ones, using the energy of the cell. The leading role in the processes of photosynthesis is played by photosynthetic pigments, which have the unique property of capturing light and converting its energy into chemical energy. Photosynthetic pigments are a fairly large group of protein-like substances. The main and most important energy-wise is pigment. chlorophyll a, found in all phototrophs except photosynthetic bacteria. Photosynthetic pigments are embedded in the inner membrane of plastids in eukaryotes or in invaginations of the cytoplasmic membrane in prokaryotes.
During the process of photosynthesis, in addition to monosaccharides (glucose, etc.), which are converted into starch and stored by the plant, monomers of other organic compounds are synthesized - amino acids, glycerol and fatty acids. Thus, thanks to photosynthesis, plant cells, or more precisely, chlorophyll-containing cells, provide themselves and all living things on Earth with the necessary organic substances and oxygen.
5. Chemosynthesis
Chemosynthesis is also the process of synthesizing organic compounds from inorganic ones, but it is carried out not at the expense of light energy, but at the expense of chemical energy obtained during oxidation inorganic substances(sulfur, hydrogen sulfide, iron, ammonia, nitrite, etc.). Highest value have nitrifying, iron and sulfur bacteria.
The energy released during oxidation reactions is stored by bacteria in the form of ATP and used for the synthesis of organic compounds. Chemosynthetic bacteria play a very important role in the biosphere. They participate in wastewater treatment, contribute to the accumulation of minerals in the soil, and increase soil fertility.
Metabolism of substances and energy (metabolism) occurs at all levels of the body: cellular, tissue and organismal. It ensures the constancy of the internal environment of the body - homeostasis - in continuously changing conditions of existence. Two processes occur simultaneously in a cell: plastic metabolism (anabolism or assimilation) and energy metabolism (fatabolism or dissimilation).
Plastic exchange is the totality of all synthesis processes when complex substances are formed from simple substances, while energy is expended.
Energy metabolism is the totality of all splitting processes when complex substances are formed into simple ones and energy is released.
Homeostasis is maintained by the balance between plastic and energy metabolism. If this balance is disturbed, then pathologies (diseases) arise in the body or part of it.
Metabolism occurs when normal temperature, pressure and a certain pH environment
11.Energy metabolism in the cell.
Energy metabolism is a set of chemical reactions of the gradual breakdown of organic compounds, accompanied by the release of energy, part of which is spent on the synthesis of ATP. Synthesized ATP becomes a universal source of energy for the life of organisms.
Stages of energy metabolism:
1. Preparatory - on it complex substances are broken down into simple ones, for example polysaccharides into monosaccharides. This stage occurs in the cytoplasm and releases energy, but very little energy is therefore dissipated as heat.
2. Oxygen-free - in lysosomes, at this stage the breakdown of substances into simpler ones continues without the participation of oxygen with the release of two ATP molecules
3. Oxygen - it continues the breakdown of substances with the participation of oxygen to the final products (carbon dioxide and water) with the release of 36 ATP. This process occurs in mitochondria.
Cell nutrition. Chemosynthesis
Cell nutrition occurs as a result of a series of complex chemical reactions, during which substances that enter the cell from the external environment (carbon dioxide, mineral salts, water) enter the body of the cell itself in the form of proteins, sugars, fats, oils, nitrogen and phosphorus. connections.
All living organisms can be divided into 2 groups:
1. Autotrophic type of nutrition - these include organisms that themselves synthesize organic compounds from inorganic ones.
2 types of autotrophs:
Photosynthetics are autotrophs that use energy sunlight(plants, cyanobacteria, protozoa)
Chemosynthetics are organisms that use energy chemical bonds. This type includes almost all bacteria (nitrogen fixers, sulfur bacteria, iron bacteria)
Chemosynthesis was discovered by Vinogradov.
Chemosynthesis is a method of autotrophic nutrition in which oxidation reactions serve as the energy source for the synthesis of organic substances from CO2 inorganic compounds. This option for obtaining energy is used only by bacteria or archaea.
2. Heterotrophic type of nutrition - characteristic of organisms that feed on ready-made organic compounds.
Soprophytes are heterotrophs that feed on dead tissues or organisms (crows, vultures, hyenas..)
Plant-eating - heterotrophs that eat plant organisms (herbivores)
Carnivores (predators) are heterotrophs that catch and eat other organisms (insectivores)
Omnivores - eat plant and animal foods
3. Mixotrophic type of nutrition - combines autotrophic and heterotrophic types of nutrition (sundew, green euglena)
Photosynthesis
Photosynthesis is a complex process of formation of inorganic substances using the energy of sunlight. The main organ of photosynthesis is the leaf because it contains the most chloroplasts and its shape is most suitable for receiving sunlight.
Phases of photosynthesis:
1. Light phase - includes 2 main processes: photolysis of water and non-cyclic phosphorylation.
Thylakoids are flattened membrane sacs on which chlorophyll pigments and a special electron carrier called cytochrome are located.
There are 2 photo systems located on the thylakoids:
Photosystem 1 contains chlorophyll a1, which perceives a light quantum with a length of 700 nanometers
Photosystem 2 contains chlorophyll a2, which perceives a light quantum with a length of 680 nanometers
When a quantum of light hits photosystem 1, the electrons of chlorophyll a1 are excited and transferred to a process such as the fatolysis of water, i.e. Water is split into hydrogen and a hydroxo group. Hydrogen is used to reduce the substance. The resulting hydroxo group accumulates and is converted into water and oxygen, which leaves the cell.
When a light quantum hits photosystem 2, the electrons of chlorophyll are excited under the influence of light and a phosphoric acid residue is added to the ADP molecule due to energy, resulting in an ATP molecule.
The light phase occurs on thylakods, where the energy necessary for the formation of organic substances is generated.
Dark phase - occurs in the stroma, independent of sunlight. Here, in the course of complex reactions, carbon dioxide is converted into glucose using the energy generated. These reactions are called the Calvin cycle.
Genetic code
This is a method characteristic of all living organisms of encoding the amino acid sequence of proteins using a sequence of nucleotides
DNA can contain 4 nitrogenous bases:
Adenine, Guanine, Thymine, Cytosine
DNA can code for 64 amino acids
Properties:
1. Degeneracy - increases the reliability of storage and transmission genetic information during cell division
2. Specificity - 1 triplet always encodes only 1 amino acid
Genetic co is universal for all living organisms from bacteria to humans
15. Transcription and broadcast
Protein synthesis includes 2 stages:
1. Transcription is the transcription of information from a DNA molecule to messenger RNA
This process takes place in the nucleus with the participation of the enzyme RNA polymerase. This enzyme determines the beginning and end of synthesis. The beginning is a specific sequence of nucleotides called a promoter. The end is also a sequence of nucleotides called a terminator.
Transcription begins with determining the section of the DNA molecule from which information will be copied
Then this section unwinds according to the principle of complementarity to one DNA strand and messenger RNA is built. After DNA synthesis is complete, it twists again.
2. Translation is the translation of the messenger RNA tucleotide sequence into an amino acid sequence
Transfer RNA carries messenger RNA to the ribosome. Here, messenger RNA is integrated into the small subunit of the ribosome, but only 2 triplets fit into it, so during synthesis, messenger RNA moves into the large subunit, transfer RNA carries amino acids, if the amino acid is suitable, then it is separated from the transfer RNA and attached to other amino acids according to the peptide principle connections.
Transfer RNA leaves the ribosome, and new transfer RNAs enter the large subunit
If the amino acid does not match the information in the small subunit according to the principle of complementarity, then this transport RNA with the amino acid leaves the ribosome
The beginning of protein synthesis is indicated by adenine, uracil, guanine, and ends with stop cadone
When protein synthesis ends, the primary structure of the protein is separated from the ribosome and the protein takes on the desired structure
Cell life cycle
The cell cycle is the period of cell existence from the moment of its formation by dividing the mother cell until its own division or death.
Interphase is the phase in the life cycle between two cell divisions. It is characterized by active metabolic processes, protein and RNA synthesis, accumulation of nutrients by the cell, growth and increase in volume. In the middle of interphase, DNA duplication (replication) occurs. As a result, each chromosome contains 2 DNA molecules and consists of two sister chromatids, which are linked by a centromere and form one chromosome. The cell prepares for division, all its organelles double. The duration of interphase depends on the cell type and averages 4/5 of the total time life cycle cells. Cell division. The growth of an organism occurs through the division of its cells. Ability to divide - most important property cellular activity. When a cell divides, it doubles all its structural components, resulting in two new cells. The most common method of cell division is mitosis - indirect cell division. Mitosis is the process of producing two daughter cells identical to the original mother cell. It ensures cell renewal during the aging process. Mitosis consists of four sequential phases:
1. Prophase - formation of chromosomes with two chromatids, destruction of the nuclear membrane.
2.Metophase—formation of the spindle, shortening of chromosomes, formation of the equaterial cell
3. Anaphase - separation of chromatids, their divergence to the poles along the spindle fibers
4. Telophase - Disappearance of the spindle, formation of nuclear membranes, discoiling of chromosomes.
Mitosis. Amitosis
Mitosis is the process of indirect division of somatic cells of eukaryotes, as a result of which the hereditary material is first doubled and then evenly distributed between daughter cells. It is the main way eukaryotic cells divide. The duration of mitosis in animal cells is 30-60 minutes, and in plant cells - 2-3 hours. It consists of 4 main phases:
1. Prophase - begins with the speralization of DNA chains to chromosomes, the nucleoli and nuclear membrane are destroyed, the chromosomes begin to float freely in the cytoplasm. At the end of prophase, the spindle begins to form
2. Metaphase - chromosomes line up strictly at the equator in the form of a metaphase plate. The spindle threads, which are already fully formed, pass through the centromeres of the chromosomes dividing the chromosome into 2 chromatids
3. Anaphase - Here the spindle filaments separate and stretch to different poles of the chromatid. The fission spindle begins to collapse.
4. Telophase Here, at the poles of the cell, the chromatids are dispersed, covered with a nuclear membrane, and the division of the cytoplasm and the cell itself begins.
As a result of mitosis, 2 identical diploid cells are formed.
Karyokenesis is nuclear division
Cytokenesis is the division of the cytoplasm and the cell itself
Amitosis is the direct division of the nucleus resulting in the formation of a cell with two nuclei, this type is characteristic of muscle cells and connective tissues
This is necessary for the full organization of cell work.
If suddenly such a cell divides, then the new cells will contain an incomplete genetic set, which will lead to their death or make them a pathogen.
Meiosis
This is an indirect division of germ cells resulting in the formation of 4 haploid daughter cells with different genetic materials. This is the main stage in the formation of germ cells.
Biological significance of meiosis:
1. Thanks to meiosis, genetically different gametes are formed
2. The constancy of the diploid set of chromosomes in somatic cells is maintained
3. Thanks to meiosis, 1 cell produces 4 new cells
Meiosis includes 2 divisions:
Reduction - during this division the number of chromosomes decreases
Equational - proceeds the same way as mitosis
Interphase proceeds in the same way as mitosis, i.e. DNA doubles in the nucleus of a dividing cell.
1 meiotic division
Prophase is the most complex and longest phase of meiosis because 2 additional processes appear here.
1- Conjugation is a close approach of homologous chromosomes resulting in the formation of 4 chromatids united by 1 centromere and such a structure will be called a bivalent. Then crossing over occurs between the chromosomes that are united into a bivalent.
2- Crossing over - exchange of chromosome sections. As a result of these processes, 1 gene recombination occurs
Metaphase - here, at the equator of the cell, bivalents form a metaphase plate, through the centromeres of which the filaments of the spindle also pass
Anaphase - unlike mitosis, here whole chromosomes disperse to the poles of the cell. 2 gene recombinations take place here
Telophase - in animals and some plants, chromosomes begin to unwind, become covered with a nuclear membrane at the poles and split into 2 cells (only in animals)
In plants, after anaphase, prophase 2 immediately occurs.
Interphase - characteristic only of animals; unlike the interphase of mitosis, there is no increase in hereditary information
Division 2 of meiosis includes prophase, metaphase, telophase, anaphase, which proceed exactly as in mitosis but with fewer chromosomes.
Asexual reproduction.
This is a type of reproduction that is characterized by:
2. 1 individual participates
3. occurs under favorable conditions
4. all organisms turn out the same
5. retains the properties and characteristics of stably unchanging conditions
Biological significance:
1. necessary for the emergence of organisms with identical anatomical properties
2. in evolutionary terms, asexual reproduction is not beneficial, but thanks to this reproduction in short time the number of individuals within the population increases
Types of asexual reproduction:
Mitotic division - occurs due to mitosis (amoeba, algae, bacteria...)
Sporulation is carried out through spores, specialized cells of fungi and plants. If a spore has a flagellum, then it is called a zoospore and is characteristic of an aquatic environment (spores, fungi, lichens..)
Humping - on the mother individual, an outgrowth occurs - a bud (contains a daughter nucleus) from which a new individual develops. The bud grows and reaches the size of the mother individual, only then separates from it (Hydra, yeast fungi, sucking ciliates)
Vegetative - characteristic of many groups of plants, a new individual develops either from special structures or from part of the mother individual.
Some multicellular animals also have vegetative propagation(sponges, sea stars, flatworms)
Sexual reproduction
Characteristic:
1.2 organizations participate
2. germ cells are involved
3. children turn out to be diverse
4. in evolutionary terms, it appeared later than asexual
5. occurs under unfavorable conditions
Biological significance:
1. offspring adapt better to changing conditions environment and more viable
2. new organisms arise
Pathogenesis (virgin reproduction)
Daughter organisms develop from unfertilized eggs.
The meaning of pathogenesis:
1. Reproduction is possible with rare contacts of organisms of different sexes
2. Necessary for maximizing numbers in populations with high mortality
3. For a seasonal increase in numbers in some populations
1. Obligate (obligatory) - found in populations where only female individuals (Caucasian rock lizard)
2. Cyclic (seasonal) - characteristic of aphids, plankton, daphnia, found in populations that hysterically die out in a certain season.
3. Facultative (not obligatory) - found in social insects. Males emerge from unfertilized eggs, and worker insects emerge from fertilized eggs.
Development of germ cells
Gametogenesis
Gametes are sex cells that fuse to form a zygote from which a new organism develops.
Difference between somatic cells and germ cells:
1 gametes carry a haploid set of chromosomes, and somatic ones carry a diploid
2. gametes do not divide, but somatic ones do
3. gametes, especially eggs larger than somatic cells
Gametogenesis is the formation of germ cells that occur in the gonads-genads (ovaries, testes)
Oogenesis is gametogenesis that occurs in female body and leads to the formation of female reproductive cells (ovum)
Spermatogenesis is gametogenesis, which occurs in the male body and leads to the formation of male gametes (sperm)
Gametogenesis consists of several stages:
1. Reproduction - Here, from the primary germ cells, which are called spermatogonia and oogonia, the number of future gametes increases through mitosis. Spermatogonia reproduce throughout the entire reproductive period in the male body.
In the female body, stage 1 occurs between 2 and 5 months of intrauterine development.
2. Growth - primary germ cells increase in size and turn into first-order oocytes and spermatocytes. These cells are formed in interphase. At this stage, meiosis begins.
3. Maturation - occurs in two successive divisions - reduction and equationation. As a result of the 1st division of meiosis, second-order oocytes and spermatocytes are formed; after the 2nd division of meiosis, 4 spermotids are formed from spermatocytes.
From second-order oocytes, 1 large egg and 3 reduction bodies are formed. This is due to the fact that all the energy and nutrients go to form 1 large gamete and the remaining 3 cells do not have enough strength to form.
Therefore, 3 reduction bodies in the reproduction code are split
4. Formation - at this stage, spermatids, i.e. fully formed germ cells, grow, develop, acquire a flagellum and the shape of an adult germ cell. Spermatids are produced from spermatozoa.
Spermatozoa are formed by a head, neck and tail.
The egg is similar to a somatic cell, only it is larger in size and has additional membranes.
Fertilization
This is the process of fusion of germ cells resulting in the formation of a zygote - this is the first cell of a new organism
1. External - with this type of fertilization, the female postpones play, and the male waters her with seminal fluid. This type occurs only in aquatic environments. No special reproductive structures are required, a large amount of hereditary material is produced and the survival rate of the offspring is minimal.
2. Internal - in this type, male reproductive cells are placed in the female reproductive tract. This type requires special reproductive structures. Less hereditary material is produced. The survival rate of offspring increases. As soon as male reproductive cells enter the female’s reproductive tract, they purposefully move towards the egg, when one of the sperm penetrates the egg, its membranes become denser and it becomes inaccessible to other sperm. This is necessary to maintain the diploidity of organisms.
Double fertilization
Characteristic only for angiosperms. In the stamens, the primary male germ cells divide by meiosis, forming 4 microspores, each microspore is again divided into 2 cells (vegetative and generative)
These cells are covered with a double membrane, forming a pollen grain
In the pistil, 1 megaspore is formed from the primary female cell by meiosis and 3 cells die. The resulting megaspore is still divided into 2 cells, 1 occupies a central place in the spore, and 2 goes down
The pollen grain lands on the stigma of the pistil, the vegetative cell germinates, forming a pollen tube until the ovary. A generative cell descends through this tube, and it divides into 2 sperm. 1 sperm fertilizes the central cell from which the endosperm is formed.
2 sperm fertilize the second cell from which the embryo develops.
Ontogenesis
This is the individual development of the zygote (organism) until its death. The term was established in 1866 by Ernest Haeckel
In mammals, otnogenesis is regulated by the nervous and endocrine systems
1. Larval - in this type, emerging from the egg shells, the organism remains at the larval stage for some period, then undergoes metamorphosis (transformation into an adult)
2. Oviparous - with this type of development, the organism remains in the egg membranes for a long time and there is no larval stage
3. Intrauterine - here the development of the body takes place inside the mother’s body
Periods of ontogenesis:
1. Embryonic (intrauterine) from conception to birth
2. Postembryonic - from birth to death
Embryonic period
3 stages of development
1. Crushing
Begins a few hours after fertilization. Here the zygote begins to divide mitotically into 2 cells (blastomeres). These cells do not diverge and do not grow. Then these cells divide again and form 4 cells, this continues until 32 cells are formed, until a morula is formed - this is an embryo consisting of 32 small cells resembling a raspberry and the size of a zygote.
This morula descends along the oviduct into the uterine cavity and implants into its wall. This occurs 6 hours after fertilization.
Then the morula cells continue to divide and a blastula is formed - this is an embryo consisting of several hundred cells located in 1 layer. The blastula has a cavity and its size is the same as that of the zygote
2. Gastrulation
Contains blastula and gastrula
The blastula continues to divide and at one end cell division is more intense. This leads to the invagination of these cells into the blastula, i.e. a gastrula is formed
The gastrula is a two-layer embryo with a primary mouth, which in mammals and higher organisms during development turns into the anus. And the true mouth is formed at the other end. The gastrula cavity is the primary cell.
The outer layer of cells is the ectoderm (1 germ layer)
Inner layer cells are endoderm (2 pack sheets)
Then, between the ectoderm and endoderm, 3 germ layers (mesoderm) are formed symmetrically at both ends of the primary mouth.
3.Organogenesis
At this stage, the neurula is formed; on the dorsal part of the embryo, the outer layer of cells forms a groove, which closes and forms the neural tube. In parallel with this process, the intestinal tube is formed from the endoderm. And from the mesoderm the notochord is formed. Formed from ectoderm nervous system and sensory organs, also mortuary epithelium and its derivatives (hair, nails)
endoderm - forms digestive system and digestive glands, respiratory system, thyroid gland.
4. Mesoderm
The musculoskeletal system, circulatory, excretory, reproductive system.
Postembryonic period
Postembryonic development can go in two ways:
Direct and indirect: with complete and incomplete transformation
Direct development is typical for birds, fish, mammals, and humans. A new individual, when born and emerging from the egg shells, is similar to an adult individual, but small in size, with different proportions, with an underdeveloped nervous and reproductive system, and the integument may also differ.
During postembryonic development, the nervous and reproductive systems further develop. The cover changes and the body undergoes training and education.
Indirect development - with this type, the larval stage is present in postembryonic development. The larva bears little or no resemblance to the adult. She grows intensively, develops and eats a lot of food.
With this type of indirect development, the organism, emerging from the egg, goes through the stage of a larva, which will turn into a pupa and the larva will completely collapse into organic compounds from which a new organism will be built. An adult individual (imago) emerges from the pupa.
egg-larva-pupa-imago
Amphibians and some insects develop with incomplete transformation
There is no pupa here and metamorphosis occurs during the larval stage.
Egg-larva-adult
26. The position of man with the system of the animal world.
