Cell organelles. Structure and functions. Eukaryotic cells First eukaryotic cells

The cells that form the tissues of animals and plants vary significantly in shape, size and internal structure. However, they all show similarities in the main features of life processes, metabolism, irritability, growth, development, and the ability to change.

Cells of all types contain two main components, closely related to each other - the cytoplasm and the nucleus. The nucleus is separated from the cytoplasm by a porous membrane and contains nuclear sap, chromatin and the nucleolus. Semi-liquid cytoplasm fills the entire cell and is penetrated by numerous tubules. On the outside it is covered with a cytoplasmic membrane. It has specialized organelle structures, permanently present in the cell, and temporary formations - inclusions.Membrane organelles : outer cytoplasmic membrane (OCM), endoplasmic reticulum (ER), Golgi apparatus, lysosomes, mitochondria and plastids. The structure of all membrane organelles is based on a biological membrane. All membranes have a fundamentally uniform structural plan and consist of a double layer of phospholipids, into which protein molecules are immersed at different depths on different sides. The membranes of organelles differ from each other only in the sets of proteins they contain.

Scheme of the structure of a eukaryotic cell. A - cell of animal origin; B - plant cell: 1 - nucleus with chromatin and nucleolus, 2 - cytoplasmic membrane, 3 - cell wall, 4 - pores in the cell wall through which the cytoplasm of neighboring cells communicates, 5 - rough endoplasmic reticulum, b - smooth endoplasmic reticulum, 7 - pinocytotic vacuole, 8 - Golgi apparatus (complex), 9 - lysosome, 10 - fatty inclusions in the channels of the smooth endoplasmic reticulum, 11 - cell center, 12 - mitochondria, 13 - free ribosomes and polyribosomes, 14 - vacuole, 15 - chloroplast

Cytoplasmic membrane. All plant cells, multicellular animals, protozoa and bacteria have a three-layer cell membrane: the outer and inner layers consist of protein molecules, the middle layer consists of lipid molecules. It limits the cytoplasm from the external environment, surrounds all cell organelles and is a universal biological structure. In some cells, the outer membrane is formed by several membranes tightly adjacent to each other. In such cases, the cell membrane becomes dense and elastic and allows the cell to maintain its shape, as, for example, in euglena and slipper ciliates. Most plant cells, in addition to the membrane, also have a thick cellulose shell on the outside - cell wall. It is clearly visible in a conventional light microscope and performs a supporting function due to the rigid outer layer, which gives the cells a clear shape.

On the surface of cells, the membrane forms elongated outgrowths - microvilli, folds, invaginations and protrusions, which greatly increases the absorption or excretory surface. With the help of membrane outgrowths, cells connect with each other in the tissues and organs of multicellular organisms; various enzymes involved in metabolism are located on the folds of the membranes. By delimiting the cell from the environment, the membrane regulates the direction of diffusion of substances and at the same time actively transports them into the cell (accumulation) or out (excretion). Due to these properties of the membrane, the concentration of potassium, calcium, magnesium, and phosphorus ions in the cytoplasm is higher, and the concentration of sodium and chlorine is lower than in the environment. Through the pores of the outer membrane, ions, water and small molecules of other substances penetrate into the cell from the external environment. Penetration of relatively large solid particles into the cell is carried out by phagocytosis(from the Greek “phago” - devour, “drink” - cell). In this case, the outer membrane at the point of contact with the particle bends into the cell, drawing the particle deep into the cytoplasm, where it undergoes enzymatic cleavage. Drops of liquid substances enter the cell in a similar way; their absorption is called pinocytosis(from the Greek “pino” - drink, “cytos” - cell). The outer cell membrane also performs other important biological functions.

Cytoplasm 85% consists of water, 10% - proteins, the rest of the volume accounts for lipids, carbohydrates, nucleic acids and mineral compounds; all these substances form a colloidal solution similar in consistency to glycerin. The colloidal substance of a cell, depending on its physiological state and the nature of the influence of the external environment, has the properties of both a liquid and an elastic, denser body. The cytoplasm is penetrated by channels of various shapes and sizes, which are called endoplasmic reticulum. Their walls are membranes that are in close contact with all organelles of the cell and together with them constitute a single functional and structural system for the metabolism and energy and movement of substances within the cell.

The walls of the tubules contain tiny granules called ribosomes. This network of tubules is called granular. Ribosomes can be located scattered on the surface of the tubules or form complexes of five to seven or more ribosomes, called polysomes. Other tubules do not contain granules; they form a smooth endoplasmic reticulum. Enzymes involved in the synthesis of fats and carbohydrates are located on the walls.

The internal cavity of the tubules is filled with waste products of the cell. Intracellular tubules, forming a complex branching system, regulate the movement and concentration of substances, separate various molecules of organic substances and the stages of their synthesis. On the inner and outer surfaces of membranes rich in enzymes, proteins, fats and carbohydrates are synthesized, which are either used in metabolism, or accumulate in the cytoplasm as inclusions, or are excreted.

Ribosomes found in all types of cells - from bacteria to cells of multicellular organisms. These are round bodies consisting of ribonucleic acid (RNA) and proteins in almost equal proportions. They certainly contain magnesium, the presence of which maintains the structure of ribosomes. Ribosomes can be associated with the membranes of the endoplasmic reticulum, with the outer cell membrane, or lie free in the cytoplasm. They carry out protein synthesis. In addition to the cytoplasm, ribosomes are found in the cell nucleus. They are formed in the nucleolus and then enter the cytoplasm.

Golgi complex in plant cells it looks like individual bodies surrounded by membranes. In animal cells, this organelle is represented by cisterns, tubules and vesicles. Cell secretion products enter the membrane tubes of the Golgi complex from the tubules of the endoplasmic reticulum, where they are chemically rearranged, compacted, and then pass into the cytoplasm and are either used by the cell itself or removed from it. In the tanks of the Golgi complex, polysaccharides are synthesized and combined with proteins, resulting in the formation of glycoproteins.

Mitochondria- small rod-shaped bodies bounded by two membranes. Numerous folds - cristae - extend from the inner membrane of the mitochondrion; on their walls there are various enzymes, with the help of which the synthesis of a high-energy substance - adenosine triphosphoric acid (ATP) is carried out. Depending on the activity of the cell and external influences, mitochondria can move, change their size and shape. Ribosomes, phospholipids, RNA and DNA are found in mitochondria. The presence of DNA in mitochondria is associated with the ability of these organelles to reproduce by forming a constriction or budding during cell division, as well as the synthesis of some mitochondrial proteins.

Lysosomes- small oval formations, bounded by a membrane and scattered throughout the cytoplasm. Found in all cells of animals and plants. They arise in extensions of the endoplasmic reticulum and in the Golgi complex, here they are filled with hydrolytic enzymes, and then separate and enter the cytoplasm. Under normal conditions, lysosomes digest particles that enter the cell by phagocytosis and organelles of dying cells. Lysosome products are excreted through the lysosome membrane into the cytoplasm, where they are included in new molecules. When the lysosome membrane ruptures, enzymes enter the cytoplasm and digest its contents, causing cell death.

Plastids found only in plant cells and found in most green plants. Organic substances are synthesized and accumulated in plastids. There are three types of plastids: chloroplasts, chromoplasts and leucoplasts.

Chloroplasts - green plastids containing the green pigment chlorophyll. They are found in leaves, young stems, and unripe fruits. Chloroplasts are surrounded by a double membrane. In higher plants, the internal part of the chloroplasts is filled with a semi-liquid substance, in which the plates are laid parallel to each other. Paired membranes of the plates, merging, form stacks containing chlorophyll (Fig. 6). In each stack of chloroplasts of higher plants, layers of protein molecules and lipid molecules alternate, and chlorophyll molecules are located between them. This layered structure provides maximum free surfaces and facilitates the capture and transfer of energy during photosynthesis.

Chromoplasts - plastids containing plant pigments (red or brown, yellow, orange). They are concentrated in the cytoplasm of cells of flowers, stems, fruits, and leaves of plants and give them the appropriate color. Chromoplasts are formed from leucoplasts or chloroplasts as a result of the accumulation of pigments carotenoids.

Leukoplasts - colorless plastids located in uncolored parts of plants: in stems, roots, bulbs, etc. Starch grains accumulate in the leucoplasts of some cells, oils and proteins accumulate in the leucoplasts of other cells.

All plastids arise from their predecessors - proplastids. They revealed DNA that controls the reproduction of these organelles.

Cell center, or centrosome, plays an important role in cell division and consists of two centrioles . It is found in all animal and plant cells, except for flowering fungi, lower fungi and some protozoa. Centrioles in dividing cells take part in the formation of the division spindle and are located at its poles. In a dividing cell, the cell center is the first to divide, and at the same time an achromatin spindle is formed, which orients the chromosomes as they diverge to the poles. One centriole leaves each of the daughter cells.

Many plant and animal cells have special purpose organoids: cilia, performing the function of movement (ciliates, respiratory tract cells), flagella(protozoa unicellular, male reproductive cells in animals and plants, etc.). Inclusions - temporary elements that arise in a cell at a certain stage of its life as a result of a synthetic function. They are either used or removed from the cell. Inclusions are also reserve nutrients: in plant cells - starch, droplets of fat, blocks, essential oils, many organic acids, salts of organic and inorganic acids; in animal cells - glycogen (in liver cells and muscles), drops of fat (in subcutaneous tissue); Some inclusions accumulate in cells as waste - in the form of crystals, pigments, etc.

Vacuoles - these are cavities bounded by a membrane; well expressed in plant cells and present in protozoa. They arise in different areas of the endoplasmic reticulum. And they gradually separate from it. Vacuoles maintain turgor pressure; cellular or vacuolar sap is concentrated in them, the molecules of which determine its osmotic concentration. It is believed that the initial products of synthesis - soluble carbohydrates, proteins, pectins, etc. - accumulate in the cisterns of the endoplasmic reticulum. These clusters represent the rudiments of future vacuoles.

Cytoskeleton . One of the distinctive features of a eukaryotic cell is the development in its cytoplasm of skeletal formations in the form of microtubules and bundles of protein fibers. The elements of the cytoskeleton are closely associated with the outer cytoplasmic membrane and the nuclear envelope and form complex weaves in the cytoplasm. The supporting elements of the cytoplasm determine the shape of the cell, ensure the movement of intracellular structures and the movement of the entire cell.

Core The cell plays a major role in its life; with its removal, the cell ceases its functions and dies. Most animal cells have one nucleus, but there are also multinucleated cells (human liver and muscles, fungi, ciliates, green algae). Mammalian red blood cells develop from precursor cells containing a nucleus, but mature red blood cells lose it and do not live long.

The nucleus is surrounded by a double membrane, permeated with pores, through which it is closely connected with the channels of the endoplasmic reticulum and the cytoplasm. Inside the core is chromatin- spiralized sections of chromosomes. During cell division, they turn into rod-shaped structures that are clearly visible under a light microscope. Chromosomes are complex complexes of proteins and DNA called nucleoprotein.

The functions of the nucleus are to regulate all the vital functions of the cell, which it carries out with the help of DNA and RNA material carriers of hereditary information. In preparation for cell division, DNA doubles; during mitosis, chromosomes separate and are passed on to daughter cells, ensuring the continuity of hereditary information in each type of organism.

Karyoplasm - liquid phase of the nucleus, in which the waste products of nuclear structures are found in dissolved form

Nucleolus- isolated, densest part of the core. The nucleolus contains complex proteins and RNA, free or bound phosphates of potassium, magnesium, calcium, iron, zinc, as well as ribosomes. The nucleolus disappears before the start of cell division and is re-formed in the last phase of division.

Thus, the cell has a fine and very complex organization. The extensive network of cytoplasmic membranes and the membrane principle of the structure of organelles make it possible to distinguish between the many chemical reactions occurring simultaneously in the cell. Each of the intracellular formations has its own structure and specific function, but only through their interaction is the harmonious functioning of the cell possible. Based on this interaction, substances from the environment enter the cell, and waste products are removed from it into the external environment - this is how metabolism occurs. The perfection of the structural organization of a cell could only arise as a result of long-term biological evolution, during which the functions it performed gradually became more complex.

The simplest unicellular forms represent both a cell and an organism with all its life manifestations. In multicellular organisms, cells form homogeneous groups - tissues. In turn, tissues form organs, systems, and their functions are determined by the general vital activity of the whole organism.

Eukaryotes, or nuclear cells, are much more complex than prokaryotes. The structure of a eukaryotic cell is aimed at carrying out intracellular metabolism.

Plasmalemma

Outside, any cell is surrounded by a thin elastic plasma membrane called the plasmalemma. The plasmalemma contains organic substances described in the table.

Rice. 1. Structure of the plasmalemma.

Above the plasmalemma of a plant cell is a cell wall, which contains cellulose. It maintains shape and limits cell mobility. An animal cell is covered with a glycocalyx consisting of various organic compounds. The main function of additional coatings is protection.

Through the plasmalemma, substances are transported and signals are transmitted through built-in proteins.

Core

Eukaryotes differ from prokaryotes by having a nucleus - a membrane structure, consisting of three components:

• two membranes having pores;
• nucleoplasm - a liquid consisting of chromatin (contains RNA and DNA), protein, nucleic acids, water;
• nucleolus - a compacted portion of the nucleoplasm.

Rice. 2. Structure of the nucleus.

The nucleus controls all cell processes and also carries out:

TOP 4 articleswho are reading along with this

• storage and transmission of hereditary information;
• ribosome formation;
• synthesis of nucleic acids.

Cytoplasm

The cytoplasm of eukaryotes contains various organelles that carry out metabolism due to the constant movement of the cytoplasm (cyclosis). Their description is presented in the table of the structure of a eukaryotic cell.

A plant cell is characterized by two special organelles that are absent in animals:

• vacuole - accumulates organic substances, water, maintains turgor;
• plastids - depending on the species, they carry out photosynthesis (chloroplasts), accumulate substances (leukoplasts), and color flowers and fruits (chromoplasts).

In animal cells (absent in plants) there is a centrosome (cellular center), which collects microtubules, from which the spindle, cytoskeleton, flagella and cilia are subsequently formed.

Rice. 3. Plant and animal cells.

Eukaryotes reproduce by division - mitosis or meiosis. Mitosis (indirect division) is characteristic of all somatic (non-reproductive) cells and single-celled nuclear organisms. Meiosis is the process of formation of gametes.

What have we learned?

From the 9th grade biology lesson we learned briefly about the structure and functions of a eukaryotic cell. Eukaryotes are complex structures consisting of a cell membrane, cytoplasm and nucleus. In the cytoplasm of a eukaryotic cell there are various organelles (Golgi complex, EPS, lysosomes, etc.) that carry out intracellular metabolism. In addition, plant cells are characterized by a vacuole and plastids, and animal cells are characterized by a cell center.

Test on the topic

Evaluation of the report

Average rating: 4.1. Total ratings received: 300.

Cell structure

Cell structure

Prokaryotic cell

Prokaryotes(from lat. pro

Chromosome structure

Scheme of the chromosome structure in late prophase - metaphase of mitosis. 1-chromatid; 2-centromere; 3-short shoulder; 4-long shoulder.

Chromosomes(ancient Greek χρῶμα - color and σῶμα - body) - nucleoprotein structures in the nucleus of a eukaryotic cell (a cell containing a nucleus), which become easily visible in certain phases of the cell cycle (during mitosis or meiosis). Chromosomes represent a high degree of condensation of chromatin that is constantly present in the cell nucleus. Initially, the term was proposed to refer to structures found in eukaryotic cells, but in recent decades they are increasingly talking about bacterial chromosomes. Most of the hereditary information is concentrated in chromosomes.

Chromosome morphology is best seen in a cell at the metaphase stage. A chromosome consists of two rod-shaped bodies - chromatids. Both chromatids of each chromosome are identical to each other in gene composition.

Chromosomes are differentiated by length. Chromosomes have a centromere or primary constriction, two telomeres and two arms. On some chromosomes, secondary constrictions and satellites are distinguished. The movement of the chromosome is determined by the centromere, which has a complex structure.

Centromere DNA is distinguished by a characteristic nucleotide sequence and specific proteins. Depending on the location of the centromere, acrocentric, submetacentric and metacentric chromosomes are distinguished.

As mentioned above, some chromosomes have secondary constrictions. They, unlike the primary constriction (centromere), do not serve as a site for attachment of spindle threads and do not play any role in the movement of chromosomes. Some secondary constrictions are associated with the formation of nucleoli, in which case they are called nucleolar organizers. The nucleolar organizers contain genes responsible for RNA synthesis. The function of other secondary constrictions is not yet clear.

Some acrocentric chromosomes have satellites - regions connected to the rest of the chromosome by a thin thread of chromatin. The shape and size of the satellite are constant for a given chromosome. In humans, five pairs of chromosomes have satellites.

The terminal regions of chromosomes rich in structural heterochromatin are called telomeres. Telomeres prevent chromosome ends from sticking together after reduplication and thereby help maintain their integrity. Consequently, telomeres are responsible for the existence of chromosomes as individual entities.

Chromosomes that have the same gene order are called homologous. They have the same structure (length, centromere location, etc.). Non-homologous chromosomes have different gene sets and different structures.

A study of the fine structure of chromosomes showed that they consist of DNA, protein and a small amount of RNA. The DNA molecule carries negative charges distributed along its entire length, and the proteins attached to it - histones - are positively charged. This complex of DNA and protein is called chromatin. Chromatin can have varying degrees of condensation. Condensed chromatin is called heterochromatin, decondensed chromatin is called euchromatin. The degree of chromatin decondensation reflects its functional state. Heterochromatic regions are functionally less active than euchromatic regions, in which most genes are localized. There is structural heterochromatin, the amount of which varies in different chromosomes, but it is constantly located in the pericentromeric regions. In addition to structural heterochromatin, there is facultative heterochromatin, which appears in the chromosome during supercoiling of euchromatic regions. The existence of this phenomenon in human chromosomes is confirmed by the fact of genetic inactivation of one X chromosome in the somatic cells of a woman. Its essence lies in the fact that there is an evolutionarily formed mechanism for inactivating the second dose of genes localized in the X chromosome, as a result of which, despite the different number of X chromosomes in male and female organisms, the number of genes functioning in them is equal. Chromatin is condensed to its maximum during mitotic cell division, then it can be detected in the form of dense chromosomes

The size of the DNA molecules of chromosomes is enormous. Each chromosome is represented by one DNA molecule. They can reach hundreds of micrometers and even centimeters. Of the human chromosomes, the largest is the first; its DNA has a total length of up to 7 cm. The total length of DNA molecules of all chromosomes of one human cell is 170 cm.

Despite the gigantic size of DNA molecules, it is quite densely packed in chromosomes. This specific folding of chromosomal DNA is provided by histone proteins. Histones are located along the length of the DNA molecule in the form of blocks. One block contains 8 histone molecules, forming a nucleosome (a formation consisting of a DNA strand wound around a histone octamer). The size of a nucleosome is about 10 nm. Nucleosomes look like beads strung on a thread. Nucleosomes and the sections of DNA connecting them are tightly packed in the form of a spiral; for each turn of such a spiral there are six nucleosomes. This is how the chromosome structure is formed.

The hereditary information of an organism is strictly ordered along individual chromosomes. Each organism is characterized by a certain set of chromosomes (number, size and structure), which is called a karyotype. The human karyotype is represented by twenty-four different chromosomes (22 pairs of autosomes, X and Y chromosomes). A karyotype is a species passport. Karyotype analysis allows us to identify disorders that can lead to developmental abnormalities, hereditary diseases or death of fetuses and embryos in the early stages of development.

For a long time it was believed that the human karyotype consists of 48 chromosomes. However, at the beginning of 1956, a message was published according to which the number of chromosomes in a human karyotype is 46.

Human chromosomes vary in size, location of the centromere and secondary constrictions. The first division of the karyotype into groups was carried out in 1960 at a conference in Denver (USA). The description of the human karyotype was originally based on the following two principles: the arrangement of chromosomes along their length; grouping of chromosomes according to the location of the centromere (metacentric, submetacentric, acrocentric).

The exact constancy of the number of chromosomes, their individuality and structural complexity indicate the importance of the function they perform. Chromosomes serve as the main genetic apparatus of the cell. They contain genes in a linear order, each of which occupies a strictly defined place (locus) in the chromosome. There are many genes on each chromosome, but for the normal development of the body, a set of genes of the complete chromosomal set is necessary.

Structure and functions of DNA

DNA- a polymer whose monomers are deoxyribonucleotides. A model of the spatial structure of the DNA molecule in the form of a double helix was proposed in 1953 by J. Watson and F. Crick (to build this model they used the work of M. Wilkins, R. Franklin, E. Chargaff).

DNA molecule formed by two polynucleotide chains, helically twisted around each other and together around an imaginary axis, i.e. is a double helix (with the exception of some DNA-containing viruses have single-stranded DNA). The diameter of the DNA double helix is ​​2 nm, the distance between adjacent nucleotides is 0.34 nm, and there are 10 nucleotide pairs per turn of the helix. The length of the molecule can reach several centimeters. Molecular weight - tens and hundreds of millions. The total length of DNA in the nucleus of a human cell is about 2 m. In eukaryotic cells, DNA forms complexes with proteins and has a specific spatial conformation.

DNA monomer - nucleotide (deoxyribonucleotide)- consists of residues of three substances: 1) a nitrogenous base, 2) a five-carbon monosaccharide (pentose) and 3) phosphoric acid. The nitrogenous bases of nucleic acids belong to the classes of pyrimidines and purines. DNA pyrimidine bases(have one ring in their molecule) - thymine, cytosine. Purine bases(have two rings) - adenine and guanine.

The DNA nucleotide monosaccharide is deoxyribose.

The name of a nucleotide is derived from the name of the corresponding base. Nucleotides and nitrogenous bases are indicated by capital letters.

The polynucleotide chain is formed as a result of nucleotide condensation reactions. In this case, between the 3"-carbon of the deoxyribose residue of one nucleotide and the phosphoric acid residue of another, phosphoester bond(belongs to the category of strong covalent bonds). One end of the polynucleotide chain ends with a 5" carbon (called the 5" end), the other ends with a 3" carbon (3" end).

Opposite one strand of nucleotides is a second strand. The arrangement of nucleotides in these two chains is not random, but strictly defined: thymine is always located opposite the adenine of one chain in the other chain, and cytosine is always located opposite guanine, two hydrogen bonds arise between adenine and thymine, and three hydrogen bonds arise between guanine and cytosine. The pattern according to which the nucleotides of different DNA chains are strictly ordered (adenine - thymine, guanine - cytosine) and selectively connect with each other is called the principle of complementarity. It should be noted that J. Watson and F. Crick came to understand the principle of complementarity after familiarizing themselves with the works of E. Chargaff. E. Chargaff, having studied a huge number of samples of tissues and organs of various organisms, found that in any DNA fragment the content of guanine residues always exactly corresponds to the content of cytosine, and adenine - thymine ( "Chargaff's rule"), but he could not explain this fact.

From the principle of complementarity it follows that the nucleotide sequence of one chain determines the nucleotide sequence of the other.

The DNA strands are antiparallel (multidirectional), i.e. nucleotides of different chains are located in opposite directions, and, therefore, opposite the 3" end of one chain is the 5" end of the other. The DNA molecule is sometimes compared to a spiral staircase. The “railing” of this staircase is a sugar-phosphate backbone (alternating deoxyribose and phosphoric acid residues); “steps” are complementary nitrogenous bases.

Function of DNA- storage and transmission of hereditary information.

Reparation (“repair”)

Reparations is the process of eliminating damage to the DNA nucleotide sequence. Carried out by special enzyme systems of the cell ( repair enzymes). In the process of restoring the DNA structure, the following stages can be distinguished: 1) DNA repair nucleases recognize and remove the damaged area, as a result of which a gap is formed in the DNA chain; 2) DNA polymerase fills this gap, copying information from the second (“good”) strand; 3) DNA ligase “crosslinks” nucleotides, completing repair.

Three repair mechanisms have been most studied: 1) photorepair, 2) excisional, or pre-replicative, repair, 3) post-replicative repair.

Changes in the DNA structure occur in the cell constantly under the influence of reactive metabolites, ultraviolet radiation, heavy metals and their salts, etc. Therefore, defects in repair systems increase the rate of mutation processes and cause hereditary diseases (xeroderma pigmentosum, progeria, etc.).

Structure and functions of RNA

RNA- a polymer whose monomers are ribonucleotides. Unlike DNA, RNA is formed not by two, but by one polynucleotide chain (with the exception that some RNA-containing viruses have double-stranded RNA). RNA nucleotides are capable of forming hydrogen bonds with each other. RNA chains are much shorter than DNA chains.

RNA monomer - nucleotide (ribonucleotide)- consists of residues of three substances: 1) a nitrogenous base, 2) a five-carbon monosaccharide (pentose) and 3) phosphoric acid. The nitrogenous bases of RNA also belong to the classes of pyrimidines and purines.

The pyrimidine bases of RNA are uracil, cytosine, and the purine bases are adenine and guanine. The RNA nucleotide monosaccharide is ribose.

Highlight three types of RNA: 1) informational(messenger) RNA - mRNA (mRNA), 2) transport RNA - tRNA, 3) ribosomal RNA - rRNA.

All types of RNA are unbranched polynucleotides, have a specific spatial conformation and take part in the processes of protein synthesis. Information about the structure of all types of RNA is stored in DNA. The process of synthesizing RNA on a DNA template is called transcription.

Transfer RNAs usually contain 76 (from 75 to 95) nucleotides; molecular weight - 25,000–30,000. tRNA accounts for about 10% of the total RNA content in the cell. Functions of tRNA: 1) transport of amino acids to the site of protein synthesis, to ribosomes, 2) translational intermediary. There are about 40 types of tRNA found in a cell, each of them has a unique nucleotide sequence. However, all tRNAs have several intramolecular complementary regions, due to which the tRNAs acquire a clover-leaf-like conformation. Any tRNA has a loop for contact with the ribosome (1), an anticodon loop (2), a loop for contact with the enzyme (3), an acceptor stem (4), and an anticodon (5). The amino acid is added to the 3" end of the acceptor stem. Anticodon- three nucleotides that “identify” the mRNA codon. It should be emphasized that a specific tRNA can transport a strictly defined amino acid corresponding to its anticodon. The specificity of the connection between amino acid and tRNA is achieved due to the properties of the enzyme aminoacyl-tRNA synthetase.

Ribosomal RNA contain 3000–5000 nucleotides; molecular weight - 1,000,000–1,500,000. rRNA accounts for 80–85% of the total RNA content in the cell. In complex with ribosomal proteins, rRNA forms ribosomes - organelles that carry out protein synthesis. In eukaryotic cells, rRNA synthesis occurs in the nucleoli. Functions of rRNA: 1) a necessary structural component of ribosomes and, thus, ensuring the functioning of ribosomes; 2) ensuring the interaction of the ribosome and tRNA; 3) initial binding of the ribosome and the initiator codon of the mRNA and determination of the reading frame, 4) formation of the active center of the ribosome.

Messenger RNAs varied in nucleotide content and molecular weight (from 50,000 to 4,000,000). mRNA accounts for up to 5% of the total RNA content in the cell. Functions of mRNA: 1) transfer of genetic information from DNA to ribosomes, 2) matrix for the synthesis of a protein molecule, 3) determination of the amino acid sequence of the primary structure of a protein molecule.

Structure and functions of ATP

Adenosine triphosphoric acid (ATP)- a universal source and main energy accumulator in living cells. ATP is found in all plant and animal cells. The amount of ATP averages 0.04% (of the wet weight of the cell), the largest amount of ATP (0.2–0.5%) is found in skeletal muscles.

ATP consists of residues: 1) a nitrogenous base (adenine), 2) a monosaccharide (ribose), 3) three phosphoric acids. Since ATP contains not one, but three phosphoric acid residues, it belongs to ribonucleoside triphosphates.

Most of the work that happens in cells uses the energy of ATP hydrolysis. In this case, when the terminal residue of phosphoric acid is eliminated, ATP transforms into ADP (adenosine diphosphoric acid), and when the second phosphoric acid residue is eliminated, it turns into AMP (adenosine monophosphoric acid). The free energy yield upon elimination of both the terminal and second residues of phosphoric acid is 30.6 kJ. The elimination of the third phosphate group is accompanied by the release of only 13.8 kJ. The bonds between the terminal and second, second and first residues of phosphoric acid are called high-energy (high-energy).

ATP reserves are constantly replenished. In the cells of all organisms, ATP synthesis occurs in the process of phosphorylation, i.e. addition of phosphoric acid to ADP. Phosphorylation occurs with varying intensity during respiration (mitochondria), glycolysis (cytoplasm), and photosynthesis (chloroplasts).

ATP is the main link between processes accompanied by the release and accumulation of energy, and processes occurring with energy expenditure. In addition, ATP, along with other ribonucleoside triphosphates (GTP, CTP, UTP), is a substrate for RNA synthesis.

Gene properties

1. discreteness - immiscibility of genes;
2. stability - the ability to maintain structure;
3. lability - the ability to mutate repeatedly;
4. multiple allelism - many genes exist in a population in multiple molecular forms;
5. allelicity - in the genotype of diploid organisms there are only two forms of the gene;
6. specificity - each gene encodes its own trait;
7. pleiotropy - multiple effect of a gene;
8. expressivity - the degree of expression of a gene in a trait;
9. penetrance - the frequency of manifestation of a gene in a phenotype;
10. amplification - increasing the number of copies of a gene.

Classification

1. Structural genes are unique components of the genome, representing a single sequence that encodes a specific protein or certain types of RNA. (See also the article housekeeping genes).
2. Functional genes - regulate the functioning of structural genes.

Genetic code- a method characteristic of all living organisms of encoding the amino acid sequence of proteins using a sequence of nucleotides.

DNA uses four nucleotides - adenine (A), guanine (G), cytosine (C), thymine (T), which in Russian literature are designated by the letters A, G, C and T. These letters make up the alphabet of the genetic code. RNA uses the same nucleotides, with the exception of thymine, which is replaced by a similar nucleotide - uracil, which is designated by the letter U (U in Russian-language literature). In DNA and RNA molecules, nucleotides are arranged in chains and, thus, sequences of genetic letters are obtained.

Genetic code

To build proteins in nature, 20 different amino acids are used. Each protein is a chain or several chains of amino acids in a strictly defined sequence. This sequence determines the structure of the protein, and therefore all its biological properties. The set of amino acids is also universal for almost all living organisms.

The implementation of genetic information in living cells (that is, the synthesis of a protein encoded by a gene) is carried out using two matrix processes: transcription (that is, the synthesis of mRNA on a DNA matrix) and translation of the genetic code into an amino acid sequence (synthesis of a polypeptide chain on mRNA). Three consecutive nucleotides are sufficient to encode 20 amino acids, as well as the stop signal indicating the end of the protein sequence. A set of three nucleotides is called a triplet. Accepted abbreviations corresponding to amino acids and codons are shown in the figure.

Properties

1. Triplety- a meaningful unit of code is a combination of three nucleotides (triplet, or codon).
2. Continuity- there are no punctuation marks between triplets, that is, the information is read continuously.
3. Non-overlapping- the same nucleotide cannot simultaneously be part of two or more triplets (not observed for some overlapping genes of viruses, mitochondria and bacteria, which encode several frameshift proteins).
4. Uniqueness (specificity)- a specific codon corresponds to only one amino acid (however, the UGA codon has Euplotes crassus encodes two amino acids - cysteine ​​and selenocysteine)
5. Degeneracy (redundancy)- several codons can correspond to the same amino acid.
6. Versatility- the genetic code works the same in organisms of different levels of complexity - from viruses to humans (genetic engineering methods are based on this; there are a number of exceptions, shown in the table in the section “Variations of the standard genetic code” below).
7. Noise immunity- mutations of nucleotide substitutions that do not lead to a change in the class of the encoded amino acid are called conservative; nucleotide substitution mutations that lead to a change in the class of the encoded amino acid are called radical.

Protein biosynthesis and its stages

Protein biosynthesis- a complex multi-stage process of synthesis of a polypeptide chain from amino acid residues, occurring on the ribosomes of the cells of living organisms with the participation of mRNA and tRNA molecules.

Protein biosynthesis can be divided into the stages of transcription, processing and translation. During transcription, genetic information encrypted in DNA molecules is read and this information is written into mRNA molecules. During a series of successive processing stages, some fragments that are unnecessary in subsequent stages are removed from the mRNA, and nucleotide sequences are edited. After transporting the code from the nucleus to the ribosomes, the actual synthesis of protein molecules occurs by attaching individual amino acid residues to the growing polypeptide chain.

Between transcription and translation, the mRNA molecule undergoes a series of sequential changes that ensure the maturation of the functioning matrix for the synthesis of the polypeptide chain. A cap is attached to the 5΄-end, and a poly-A tail is attached to the 3΄-end, which increases the lifespan of the mRNA. With the advent of processing in the eukaryotic cell, it became possible to combine gene exons to obtain a greater variety of proteins encoded by a single sequence of DNA nucleotides - alternative splicing.

Translation consists of the synthesis of a polypeptide chain in accordance with the information encoded in messenger RNA. The amino acid sequence is arranged using transport RNA (tRNA), which forms complexes with amino acids - aminoacyl-tRNA. Each amino acid has its own tRNA, which has a corresponding anticodon that “matches” the mRNA codon. During translation, the ribosome moves along the mRNA, and as it does so, the polypeptide chain grows. Energy for protein biosynthesis is provided by ATP.

The finished protein molecule is then cleaved from the ribosome and transported to the desired location in the cell. To achieve their active state, some proteins require additional post-translational modification.

Causes of mutations

Mutations are divided into spontaneous And induced. Spontaneous mutations occur spontaneously throughout the life of an organism under normal environmental conditions with a frequency of about 10 - 9 - 10 - 12 per nucleotide per cell generation.

Induced mutations are heritable changes in the genome that arise as a result of certain mutagenic effects in artificial (experimental) conditions or under adverse environmental influences.

Mutations appear constantly during processes occurring in a living cell. The main processes leading to the occurrence of mutations are DNA replication, DNA repair disorders and genetic recombination.

The role of mutations in evolution

With a significant change in living conditions, those mutations that were previously harmful may turn out to be useful. Thus, mutations are the material for natural selection. Thus, melanistic mutants (dark-colored individuals) in birch moth populations in England were first discovered by scientists among typical light-colored individuals in the middle of the 19th century. Dark coloring occurs as a result of a mutation in one gene. Butterflies spend the day on the trunks and branches of trees, usually covered with lichens, against which the light coloring acts as a camouflage. As a result of the industrial revolution, accompanied by air pollution, the lichens died and the light trunks of birches became covered with soot. As a result, by the middle of the 20th century (over 50-100 generations), in industrial areas the dark morph almost completely replaced the light one. It was shown that the main reason for the preferential survival of the black form was predation by birds, which selectively ate light-colored butterflies in polluted areas.

If a mutation affects “silent” sections of DNA, or leads to the replacement of one element of the genetic code with a synonymous one, then it usually does not manifest itself in the phenotype (the manifestation of such a synonymous substitution may be associated with different frequencies of codon use). However, such mutations can be detected using gene analysis methods. Since mutations most often occur as a result of natural causes, assuming that the basic properties of the external environment have not changed, it turns out that the frequency of mutations should be approximately constant. This fact can be used to study phylogeny - the study of the origin and relationships of various taxa, including humans. Thus, mutations in silent genes serve as a kind of “molecular clock” for researchers. The “molecular clock” theory also proceeds from the fact that most mutations are neutral, and the rate of their accumulation in a given gene does not depend or weakly depends on the action of natural selection and therefore remains constant for a long time. This rate will, however, differ for different genes.

The study of mutations in mitochondrial DNA (inherited on the maternal line) and in Y chromosomes (inherited on the paternal line) is widely used in evolutionary biology to study the origin of races and nationalities and reconstruct the biological development of mankind.

Cell structure

Cell structure

All cellular life forms on earth can be divided into two superkingdoms based on the structure of their constituent cells - prokaryotes (prenuclear) and eukaryotes (nuclear). Prokaryotic cells are simpler in structure; apparently, they arose earlier in the process of evolution. Eukaryotic cells are more complex and arose later. The cells that make up the human body are eukaryotic.

Despite the variety of forms, the organization of cells of all living organisms is subject to common structural principles.

The living contents of the cell - the protoplast - are separated from the environment by a plasma membrane, or plasmalemma. Inside the cell is filled with cytoplasm, in which various organelles and cellular inclusions are located, as well as genetic material in the form of a DNA molecule. Each of the cell organelles performs its own special function, and together they all determine the vital activity of the cell as a whole.

Prokaryotic cell

The structure of a typical prokaryotic cell: capsule, cell wall, plasmalemma, cytoplasm, ribosomes, plasmid, pili, flagellum, nucleoid.

Prokaryotes(from lat. pro- before, before and Greek. κάρῠον - core, nut) - organisms that, unlike eukaryotes, do not have a formed cell nucleus and other internal membrane organelles (with the exception of flat tanks in photosynthetic species, for example, cyanobacteria). The only large circular (in some species - linear) double-stranded DNA molecule, which contains the bulk of the genetic material of the cell (the so-called nucleoid), does not form a complex with histone proteins (the so-called chromatin). Prokaryotes include bacteria, including cyanobacteria (blue-green algae), and archaea. The descendants of prokaryotic cells are the organelles of eukaryotic cells - mitochondria and plastids.

Eukaryotic cell Eukaryotes(eukaryotes) (from the Greek ευ - good, completely and κάρῠον - core, nut) - organisms that, unlike prokaryotes, have a formed cell nucleus, delimited from the cytoplasm by a nuclear membrane. The genetic material is contained in several linear double-stranded DNA molecules (depending on the type of organism, their number per nucleus can range from two to several hundred), attached from the inside to the membrane of the cell nucleus and forming in the vast majority (except dinoflagellates) a complex with histone proteins called chromatin. Eukaryotic cells have a system of internal membranes that, in addition to the nucleus, form a number of other organelles (endoplasmic reticulum, Golgi apparatus, etc.). In addition, the vast majority have permanent intracellular prokaryotic symbionts - mitochondria, and algae and plants also have plastids.

Structure of a eukaryotic cell

Schematic representation of an animal cell. (By clicking on any of the names of the component parts of the cell, you will be taken to the corresponding article.)

Mitochondria and plastids have their own circular DNA and small ribosomes, through which they make part of their own proteins (semi-autonomous organelles).

Mitochondria take part in (the oxidation of organic substances) - they supply ATP (energy) for the life of the cell, and are the “energy stations of the cell.”

Non-membrane organelles

Ribosomes- these are organelles that deal with... They consist of two subunits, chemically consisting of ribosomal RNA and proteins. The subunits are synthesized in the nucleolus. Some of the ribosomes are attached to the EPS; this EPS is called rough (granular).

Cell center consists of two centrioles that form the spindle during cell division - mitosis and meiosis.

Cilia, flagella serve for movement.

Choose one, the most correct option. The cell cytoplasm contains
1) protein threads
2) cilia and flagella
3) mitochondria
4) cell center and lysosomes

Answer

Establish a correspondence between the functions and organelles of cells: 1) ribosomes, 2) chloroplasts. Write numbers 1 and 2 in the correct order.
A) located on the granular ER
B) protein synthesis
B) photosynthesis
D) consist of two subunits
D) consist of grana with thylakoids
E) form a polysome

Answer

Establish a correspondence between the structure of the cell organelle and the organelle: 1) Golgi apparatus, 2) chloroplast. Write numbers 1 and 2 in the order corresponding to the letters.
A) double membrane organelle
B) has its own DNA
B) has a secretory apparatus
D) consists of a membrane, bubbles, tanks
D) consists of thylakoids grana and stroma
E) single-membrane organelle

Answer

Establish a correspondence between the characteristics and organelles of the cell: 1) chloroplast, 2) endoplasmic reticulum. Write numbers 1 and 2 in the order corresponding to the letters.
A) a system of tubules formed by a membrane
B) the organelle is formed by two membranes
B) transports substances
D) synthesizes primary organic matter
D) includes thylakoids

Answer

1. Choose one, the most correct option. Single-membrane cell components -
1) chloroplasts
2) vacuoles
3) cell center
4) ribosomes

Answer

2. Select three options. Which cell organelles are separated from the cytoplasm by a single membrane?
1) Golgi complex
2) mitochondria
3) lysosome
4) endoplasmic reticulum
5) chloroplast
6) ribosome

Answer

All of the following features, except two, can be used to describe the structural features and functioning of ribosomes. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated.
1) consist of triplets of microtubules
2) participate in the process of protein biosynthesis
3) form the spindle
4) formed by protein and RNA
5) consist of two subunits

Answer

Choose two correct answers out of five and write down the numbers under which they are indicated in the table. Select double membrane organelles:
1) lysosome
2) ribosome
3) mitochondria
4) Golgi apparatus
5) chloroplast

Answer

Choose three correct answers out of six and write down the numbers under which they are indicated. Plant cell organelles are double-membrane.
1) chromoplasts
2) centrioles
3) leucoplasts
4) ribosomes
5) mitochondria
6) vacuoles

Answer

NUCLEUS1-MITOCHONDRIA1-RIBOSOME1
Analyze the table. For each lettered cell, select the appropriate term from the list provided:
1) core
2) ribosome
3) protein biosynthesis
4) cytoplasm
5) oxidative phosphorylation
6) transcription
7) lysosome

Answer

MITOCHONDRIA2-CHROMOSOME1-RIBOSOME2

Analyze the table “Structures of a eukaryotic cell.” For each cell indicated by a letter, select the corresponding term from the list provided.
1) glycolysis
2) chloroplasts
3) broadcast
4) mitochondria
5) transcription
6) core
7) cytoplasm
8) cell center

Answer

LYSOSOME1-RIBOSOME3-CHLOROPLAST1


1) Golgi complex
2) synthesis of carbohydrates
3) single membrane
4) starch hydrolysis
5) lysosome
6) non-membrane

Answer

LYSOSOME2-CHLOROPLAST2-RIBOSOME4

Analyze the table. For each lettered cell, select the appropriate term from the list provided.
1) double membrane
2) endoplasmic reticulum
3) protein biosynthesis
4) cell center
5) non-membrane
6) biosynthesis of carbohydrates
7) single membrane
8) lysosome

Answer

LYSOSOME3-AG1-CHLOROPLAST3
Analyze the table “Cell Structures”. For each cell indicated by a letter, select the corresponding term from the list provided.
1) glycolysis
2) lysosome
3) protein biosynthesis
4) mitochondria
5) photosynthesis
6) core
7) cytoplasm
8) cell center

Answer

CHLOROPLAST4-AG2-RIBOSOME5

Analyze the table “Cell Structures”. For each cell indicated by a letter, select the corresponding term from the list provided.
1) glucose oxidation
2) ribosome
3) splitting of polymers
4) chloroplast
5) protein synthesis
6) core
7) cytoplasm
8) spindle formation

Answer

AG3-MITOCHONDRIA3-LYSOSOME4

Analyze the table “Cell Organelles”. For each cell indicated by a letter, select the corresponding term from the list provided.
1) chloroplast
2) endoplasmic reticulum
3) cytoplasm
4) karyoplasm
5) Golgi apparatus
6) biological oxidation
7) transport of substances in the cell
8) glucose synthesis

Answer

1. Select two correct answers out of five and write down the numbers under which they are indicated in the table. Cytoplasm performs a number of functions in a cell:
1) communicates between the nucleus and organelles
2) acts as a matrix for the synthesis of carbohydrates
3) serves as the location of the nucleus and organelles
4) transmits hereditary information
5) serves as the location of chromosomes in eukaryotic cells

Answer

2. Identify two true statements from the general list, and write down the numbers under which they are indicated. Occurs in the cytoplasm
1) synthesis of ribosomal proteins
2) glucose biosynthesis
3) insulin synthesis
4) oxidation of organic substances to inorganic ones
5) synthesis of ATP molecules

Answer

Choose two correct answers out of five and write down the numbers under which they are indicated. Select non-membrane organelles:
1) mitochondria
2) ribosome
3) core
4) microtubule
5) Golgi apparatus

Answer

The following features, except two, are used to describe the functions of the cell organelle depicted. Identify two characteristics that “fall out” from the general list and write down the numbers under which they are indicated.
1) serves as an energy station
2) breaks down biopolymers into monomers
3) provides packaging of substances from the cell
4) synthesizes and accumulates ATP molecules
5) participates in biological oxidation

Answer

Establish a correspondence between the structure of the organelle and its type: 1) cell center, 2) ribosome
A) consists of two perpendicularly located cylinders
B) consists of two subunits
B) formed by microtubules
D) contains proteins that ensure the movement of chromosomes
D) contains proteins and nucleic acid

Answer

Establish the sequence of structures in a eukaryotic plant cell (starting from the outside)
1) plasma membrane
2) cell wall
3) core
4) cytoplasm
5) chromosomes

Answer

Choose three options. How are mitochondria different from lysosomes?
1) have outer and inner membranes
2) have numerous outgrowths - cristae
3) participate in the processes of energy release
4) in them, pyruvic acid is oxidized to carbon dioxide and water
5) in them biopolymers are broken down into monomers
6) participate in metabolism

Answer

1. Establish a correspondence between the characteristics of a cell organelle and its type: 1) mitochondria, 2) lysosome. Write numbers 1 and 2 in the correct order.
A) single-membrane organelle
B) internal contents - matrix

D) the presence of cristae
D) semi-autonomous organelle

Answer

2. Establish a correspondence between the characteristics and organelles of the cell: 1) mitochondria, 2) lysosome. Write numbers 1 and 2 in the order corresponding to the letters.
A) hydrolytic cleavage of biopolymers
B) oxidative phosphorylation
B) single-membrane organelle
D) the presence of cristae
D) formation of a digestive vacuole in animals

Answer

3. Establish a correspondence between the feature and the cell organelle for which it is characteristic: 1) lysosome, 2) mitochondria. Write numbers 1 and 2 in the order corresponding to the letters.
A) the presence of two membranes
B) accumulation of energy in ATP
B) the presence of hydrolytic enzymes
D) digestion of cell organelles
D) formation of digestive vacuoles in protozoa
E) breakdown of organic substances to carbon dioxide and water

Answer

Establish a correspondence between the cell organelle: 1) cell center, 2) contractile vacuole, 3) mitochondria. Write numbers 1-3 in the correct order.
A) participates in cell division
B) ATP synthesis
B) release of excess fluid
D) “cellular respiration”
D) maintaining a constant cell volume
E) participates in the development of flagella and cilia

Answer

1. Establish a correspondence between the name of organelles and the presence or absence of a cell membrane: 1) membranous, 2) non-membrane. Write numbers 1 and 2 in the correct order.
A) vacuoles
B) lysosomes
B) cell center
D) ribosomes
D) plastids
E) Golgi apparatus

Answer

2. Establish a correspondence between cell organelles and their groups: 1) membrane, 2) non-membrane. Write numbers 1 and 2 in the order corresponding to the letters.
A) mitochondria
B) ribosomes
B) centrioles
D) Golgi apparatus
D) endoplasmic reticulum
E) microtubules

Answer

3. Which three of the listed organelles are membranous?
1) lysosomes
2) centrioles
3) ribosomes
4) microtubules
5) vacuoles
6) leucoplasts

Answer

1. All but two of the cell structures listed below do not contain DNA. Identify two cell structures that “drop out” from the general list and write down the numbers under which they are indicated.
1) ribosomes
2) Golgi complex
3) cell center
4) mitochondria
5) plastids

Answer

Answer

3. 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

Answer

Choose one, the most correct option. Where in the cell are there ribosomes, except for the ER?
1) in the centrioles of the cell center
2) in the Golgi apparatus
3) in mitochondria
4) in lysosomes

Answer

What are the features of the structure and functions of ribosomes? Choose the three correct options.
1) have one membrane
2) consist of DNA molecules
3) break down organic substances
4) consist of large and small particles
5) participate in the process of protein biosynthesis
6) consist of RNA and protein

Answer

Choose three correct answers out of six and write down the numbers under which they are indicated. The structure of the nucleus of a eukaryotic cell includes
1) chromatin
2) cell center
3) Golgi apparatus
4) nucleolus
5) cytoplasm
6) karyoplasm

Answer

Choose three correct answers out of six and write down the numbers under which they are indicated. What processes occur in the cell nucleus?
1) formation of the spindle
2) formation of lysosomes
3) doubling of DNA molecules
4) synthesis of mRNA molecules
5) formation of mitochondria
6) formation of ribosomal subunits

Answer

Establish a correspondence between the cell organelle and the type of structure to which it is classified: 1) single-membrane, 2) double-membrane. Write numbers 1 and 2 in the order corresponding to the letters.
A) lysosome
B) chloroplast
B) mitochondria
D) EPS
D) Golgi apparatus

Answer

Establish a correspondence between the characteristics and organelles: 1) chloroplast, 2) mitochondria. Write numbers 1 and 2 in the order corresponding to the letters.
A) the presence of stacks of grains
B) synthesis of carbohydrates
B) dissimilation reactions
D) transport of electrons excited by photons
D) synthesis of organic substances from inorganic ones
E) the presence of numerous cristae

Answer

All of the characteristics listed below, except two, can be used to describe the cell organelle shown in the figure. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated.
1) single-membrane organelle
2) contains fragments of ribosomes
3) the shell is riddled with pores
4) contains DNA molecules
5) contains mitochondria

Answer

The terms listed below, except two, are used to characterize the cell organelle, indicated in the figure by a question mark. Identify two terms that “drop out” from the general list and write down the numbers under which they are indicated.
1) membrane organelle
2) replication
3) chromosome divergence
4) centrioles
5) spindle

Answer

Establish a correspondence between the characteristics of a cell organelle and its type: 1) cell center, 2) endoplasmic reticulum. Write numbers 1 and 2 in the order corresponding to the letters.
A) transports organic substances
B) forms a spindle
B) consists of two centrioles
D) single-membrane organelle
D) contains ribosomes
E) non-membrane organelle

Answer

1. Establish a correspondence between the characteristics and organelles of the cell: 1) nucleus, 2) mitochondria. Write the numbers 1 and 2 in the order they correspond to the numbers.
A) closed DNA molecule
B) oxidative enzymes on cristae
B) internal contents - karyoplasm
D) linear chromosomes
D) the presence of chromatin in interphase
E) folded inner membrane

Answer

2. Establish a correspondence between the characteristics and organelles of cells: 1) nucleus, 2) mitochondria. Write numbers 1 and 2 in the order corresponding to the letters.
A) is the site of ATP synthesis
B) is responsible for storing the genetic information of the cell
B) contains circular DNA
D) has cristae
D) has one or more nucleoli

Answer

Establish a correspondence between the characteristics and organelles of the cell: 1) lysosome, 2) ribosome. Write numbers 1 and 2 in the order corresponding to the letters.
A) consists of two subunits
B) is a single-membrane structure
B) participates in the synthesis of the polypeptide chain
D) contains hydrolytic enzymes
D) located on the membrane of the endoplasmic reticulum
E) converts polymers into monomers

Answer

Establish a correspondence between the characteristics and cellular organelles: 1) mitochondria, 2) ribosome. Write numbers 1 and 2 in the order corresponding to the letters.
A) non-membrane organelle
B) presence of own DNA
B) function - protein biosynthesis
D) consists of large and small subunits
D) the presence of cristae
E) semi-autonomous organelle

Answer

All of the features listed below, except two, are used to describe the cell structure shown in the figure. Identify two characteristics that “drop out” from the general list and write down the numbers under which they are indicated.
1) consists of RNA and proteins
2) consists of three subunits
3) synthesized in hyaloplasm
4) carries out protein synthesis
5) can attach to the EPS membrane

Answer

© D.V. Pozdnyakov, 2009-2019

1. Basics of cell theory

2. General plan of the structure of a prokaryotic cell

3. General plan of the structure of a eukaryotic cell

1. Basics of cell theory

The cell was first discovered and described by R. Hooke (1665). In the 19th century the foundations were laid in the works of T. Schwann and M. Schleiden cell theory structure of organisms. Modern cell theory can be expressed in the following provisions: all organisms are composed of cells; The cell is the elementary structural, genetic and functional unit of living things. The development of all organisms begins with one cell, therefore it is the elementary unit of development of all organisms. In multicellular organisms, cells specialize to perform specific functions.

Depending on the structural organization, the following forms of life are distinguished: precellular (viruses) and cellular. Among the cellular forms, based on the characteristics of the organization of cellular hereditary material, pro- and eukaryotic cells are distinguished.

Viruses- these are organisms that have very small sizes (from 20 to 3000 nm). Their life activity can only be carried out inside the cell of the host body. The body of the virus is formed by nucleic acid (DNA or RNA), which is contained in a protein shell - the capsid, sometimes the capsid is covered with a membrane.

2. General plan of the structure of a prokaryotic cell

Main components of a prokaryotic cell: membrane, cytoplasm. The membrane consists of plasmalemma and surface structures (cell wall, capsule, mucous membrane, flagella, villi).

Plasmalemma has a thickness of 7.5 nm and on the outer part is formed by a layer of protein molecules, under which there are two layers of phospholipid molecules, and then there is a new layer of protein molecules. The plasmalemma has channels lined with protein molecules; through these channels, various substances are transported, both into and out of the cell.

Main component cell wall– murein. Polysaccharides, proteins (antigenic properties), and lipids can be built into it. Gives the cell shape, prevents its osmotic swelling and rupture. Water, ions, and small molecules easily penetrate through the pores.

Cytoplasm of a prokaryotic cell performs the function of the internal environment of the cell; it contains ribosomes, mesosomes, inclusions and a DNA molecule.

Ribosomes– bean-shaped organelles, composed of protein and RNA, smaller (70S-ribosomes) than in eukaryotes. Function: protein synthesis.

Mesosomes– a system of intracellular membranes that form folded invaginations and contain enzymes of the respiratory chain (ATP synthesis).

Inclusions: lipids, glycogen, polyphosphates, proteins, storage nutrients

DNA molecule. One haploid circular double-stranded supercondensed DNA molecule. Provides storage, transmission of genetic information and regulation of cell activity.

3. General plan of the structure of a eukaryotic cell

A typical eukaryotic cell consists of three components - the membrane, the cytoplasm and the nucleus. The basis cell membrane consists of plasmalemma (cell membrane) and carbohydrate-protein surface structure.

1. Plasmalemma Eukaryotes differ from prokaryotes in having less proteins.

2. Carbohydrate-protein surface structure. Animal cells have a small layer of protein (glycocalyx). In plants, the surface structure of the cell is cell wall consists of cellulose (fiber).

Functions of the cell membrane: maintains the shape of the cell and gives mechanical strength, protects the cell, recognizes molecular signals, regulates metabolism between the cell and the environment, and carries out intercellular interaction.

Cytoplasm consists of hyaloplasm (the main substance of the cytoplasm), organelles and inclusions. The hyaloplasm contains 3 types of organelles:

double-membrane (mitochondria, plastids);

single-membrane (endoplasmic reticulum (ER), Golgi apparatus, vacuoles, lysosomes);

non-membrane (cellular center, microtubules, microfilaments, ribosomes, inclusions).

1. Hyaloplasma is a colloidal solution of organic and inorganic compounds. Hyaloplasma is capable of moving inside the cell - cyclose. The main functions of hyaloplasm: a medium for the location of organelles and inclusions, a medium for the occurrence of biochemical and physiological processes, unites all cell structures into a single whole.

2. Mitochondria(“energy stations of cells”). The outer membrane is smooth, the inner one has folds - cristae. Between the outer and inner membranes is matrix. The mitochondrial matrix contains DNA molecules, small ribosomes and various substances.

3. Plastids characteristic of plant cells. There are three types of plastids : chloroplasts, chromoplasts and leucoplasts.

I. Chloroplasts– green plastids in which photosynthesis occurs. The chloroplast has a double membrane. The chloroplast body consists of a colorless protein-lipid stroma, permeated by a system of flat sacs (thylakoids) formed by an internal membrane. Thylakoids form grana. The stroma contains ribosomes, starch grains, and DNA molecules.

II. Chromoplasts give color to different plant organs.

III. Leukoplasts store nutrients. Chromoplasts and chloroplasts can be formed from leucoplasts.

4. Endoplasmic reticulum is a branched system of tubes, channels and cavities. There are non-granular (smooth) and granular (rough) EPS. The non-granular EPS contains enzymes of fat and carbohydrate metabolism (the synthesis of fats and carbohydrates occurs). The supragranular ER contains ribosomes that carry out protein biosynthesis. Functions of EPS: mechanical and shape-forming functions; transport; concentration and release.

5. Golgi apparatus consists of flat membrane sacs and vesicles. In animal cells, the Golgi apparatus performs a secretory function. In plants, it is the center of polysaccharide synthesis.

6. Vacuoles filled with plant cell sap. Functions of vacuoles: storing nutrients and water, maintaining turgor pressure in the cell.

7 . Lysosomes– small spherical organelles, formed by a membrane, inside which contains enzymes that hydrolyze proteins, nucleic acids, carbohydrates, and fats.

8. Cellular center. The function of the cell center is to control the process of cell division.

9. Microtubules and microfilaments together form the cellular skeleton of animal cells.

10. Ribosomes eukaryotes are larger (80S).

11. Inclusions– reserve substances and secretions – only in plant cells.

Core- the most important part of a eukaryotic cell. It consists of the nuclear membrane, karyoplasm, nucleoli, and chromatin.

1. Nuclear envelope similar in structure to the cell membrane, contains pores. The nuclear membrane protects the genetic apparatus from the effects of cytoplasmic substances. Controls the transport of substances.

2. Karyoplasm is a colloidal solution containing proteins, carbohydrates, salts, and other organic and inorganic substances. The karyoplasm contains all nucleic acids: almost the entire supply of DNA, messenger, transport and ribosomal RNAs.

3. Nucleolus – spherical formation, contains various proteins, nucleoproteins, lipoproteins, phosphoproteins. The function of nucleoli is the synthesis of ribosome embryos.

4. Chromatin (chromosomes). In the steady state (time between divisions), DNA is evenly distributed in the karyoplasm in the form of chromatin. When dividing, chromatin is converted into chromosomes.

Functions of the nucleus: the nucleus contains information about the hereditary characteristics of the organism (informative function); chromosomes transmit the characteristics of an organism from parents to offspring (inheritance function); the nucleus coordinates and regulates processes in the cell (regulation function).