1. List the kingdoms of living organisms whose cells have a nucleus.
Answer. These are the kingdoms of fungi, plants, animals, that is, eukaryotes.
2. Through the works of which scientists was the cell theory created?
Answer. In 1838-1939. German scientists, botanist Matthias Schleiden and physiologist Theodor Schwann, created the so-called cell theory.
Most cells are not visible to the naked eye. However, with the help of microscopes various types Plant cells can be easily viewed and studied. In young parts of plants and fruits, the cell shapes are usually round, while in older sections the cells are box-like with 14 sides as they are packed together.
A plant cell is bounded by a cell wall, and the living part of the cell is found inside the walls and is divided into two parts: the nucleus or central control center; and cytoplasm, the fluid in which membrane-bound organelles are found. Between the primary cell walls of neighboring plant cells is a pectic middle lamina. There may be a secondary cell wall that will only be located within the inner wall. Both walls are composed primarily of cellulose, but the secondary cell wall may contain lignin and other substances.
3. What is the main difference between a prokaryotic cell and a eukaryotic cell?
Answer. All living organisms on earth are made up of cells. There are two types of cells, depending on their organization: eukaryotes and prokaryotes.
Eukaryotes are a superkingdom of living organisms. Translated from Greek language"eukaryote" means "possessing a nucleus". Accordingly, these organisms have a core in which all genetic information is encoded. These include fungi, plants and animals.
The outer boundary of protoplasm is a sandwich-like flexible plasma membrane. This membrane regulates what enters and leaves the plant cell. Plant organ cells include: the endoplasmic reticulum, with and without attached ribosomes; Golgi bodies, mitochondria and plastids. Plastids are chloroplasts, chromoplasts or leucoplasts - depending on color and similar function. Chloroplasts are of particular interest to those who study plants. It is obvious that a plant cell contains a nucleus, which is limited by a nuclear envelope with pores.
Prokaryotes are living organisms whose cells lack a nucleus. Characteristic representatives Prokaryotes are bacteria and cyanobacteria.
The first prokaryotes arose approximately 3.5 billion years ago, which 2.4 billion years later marked the beginning of the development eukaryotic cells.
Eukaryotes and prokaryotes differ greatly in size from each other. So the diameter of a eukaryotic cell is 0.01-0.1 mm, and that of a prokaryotic cell is 0.0005-0.01 mm. The volume of a eukaryote is about 10,000 times greater than that of a prokaryote.
Pores in the nuclear envelope allow the movement of substances in and out of the nucleus. Inside the nucleus there are a number of chromosomes. The number present is specific to the organism, and it will be stated later how the germ cells contain half the number of chromosomes and restore the number of chromosomes upon fertilization. All these organelles and the nucleus are suspended in the cytoplasm. The cytoplasm has movements called cytoplasmic streaming or cyclos. The specific function of other organelles contained in plant cells can be reviewed below.
How many DNA molecules form one chromosome?
The cell cycle contains a process in which cells either divide or divide between compartments. Cells that are not actively dividing are said to be in interphase, which has three distinct periods of intense activity preceding nuclear division or mitosis. The division of the rest of the cell occurs as the end result of mitosis, and this process occurs in areas of active cell division called meristems. Meristems will be covered in the Plant Tissue textbook.
Prokaryotes have circular DNA, which is located in the nucleoid. This cellular region is separated from the rest of the cytoplasm by a membrane. DNA is not connected in any way to RNA and proteins; there are no chromosomes. The DNA of eukaryotic cells is linear and is located in the nucleus, which contains chromosomes.
Prokaryotes reproduce mainly simple division in half, while eukaryotes divide by mitosis, meiosis, or a combination of the two.
Mitosis is a process within the cell cycle that is divided into four phases, which we will summarize here. Prophase - chromosomes and their normal double-stranded nature becomes apparent, the nuclear envelope breaks down. A spindle consisting of spindle fibers is developed, and some attach to chromosomes at their centromere. Anaphase - The sister chromatids of each chromosome, now called daughter chromosomes, separate along their length and each group of daughter chromosomes migrates to opposite ends of the cell. Telophase - groups of daughter chromosomes are grouped into a developing nuclear envelope, which makes them separate nuclei. A wall forms between the two sets of daughter chromosomes, creating two daughter cells. Metaphase - chromosomes align at the equator of the cell. . In plants, as the cell wall develops, droplets or vesicles of pectin coalesce to form a cell plate that will eventually become the middle plate of the new cell wall.
Eukaryotic cells have organelles characterized by the presence of their own genetic apparatus: mitochondria and plastids. They are surrounded by a membrane and have the ability to reproduce through division.
IN prokaryotic cells organelles are also found, but in smaller numbers and not limited to the membrane.
Plant cells versus animal cells
Animal cells do not have a cell wall. Instead of a cell wall, the plasma membrane is the outer boundary of animal cells. Therefore, animal tissues require either external or internal support from some kind of skeleton. Frames of tough cellulose fibrils thicken and strengthen cell walls higher plants. During the telophase of mitosis, a cell plate is formed as the plant cell begins its division. In animal cells, the cell mites form two cells in the center; no cell plate is installed.
Eukaryotes, unlike prokaryotes, have the ability to digest solid particles by enclosing them in a membrane vesicle. There is an opinion that this feature arose in response to the need to fully provide nutrition to a cell many times larger than a prokaryotic one. A consequence of the presence of phagocytosis in eukaryotes was the appearance of the first predators.
Centrioles are usually not found in more tall cells plants, while they are found in animal cells. Animal cells do not contain plastids, which are found in plant cells. Both types of cells have vacuoles, however in animal cells the vacuoles are very small or absent, whereas in plant cells the vacuoles are usually quite large. Some cells contain multiple nuclei, such as skeletal muscle, while some do not, such as red blood cells. In particular, it is responsible for storing and transmitting genetic information. The nuclear envelope consists of two membranes joined at regular intervals to form circular openings called nuclear pores. The selection process is controlled by an energy-dependent process that changes pore diameter in response to signals. Inside the nucleus is a thread-like region called the nucleolus. The nucleus is not associated with a membrane, but rather is a region. Ribosomes are the sites where protein molecules are synthesized from amino acids. Some ribosomes are found in the granular endoplasmic reticulum, while others are free in the cytoplasm. Proteins synthesized on ribosomes associated with the granular endoplasmic reticulum are transported from the lumen to the golgi apparatus for secretion outside the cell or distribution to other organelles. Proteins that are synthesized from free ribosomes are released into the cytosol. The endoplasmic reticulum is a collection of membranes covering a specific continuous space. As mentioned earlier, the granular endoplasmic reticulum is associated with ribosomes. The vesicles are then delivered to other cellular organelles and the plasma membrane. The apparatus is usually located near the nucleus. Endosomes are membrane-bound tubular and vesicular structures located between plasma membrane and the Golgi apparatus. They serve to sort and direct vesicular movement by crossing or fusing with vesicles. Mitochondria are one of the most important structures in a cage. Each mitochondria is surrounded by two membranes. Outer membrane smooth, and the inner - into tubular structures called cristae. Cells with more activity have more mitochondria, while those that are less active have less mitochondria-producing energy requirements. Lysosomes are bound by a single membrane and contain a strongly acidic liquid. The fluid acts as digestive enzymes to break down bacteria and cellular debris. They are playing important role in cells immune system. Peroxisomes are also bound by a single membrane. They consume oxygen and work on reactions that remove hydrogen from various molecules in the form of hydrogen peroxide. They are important for maintaining chemical balances within the cell. The cytoskeleton is a thread-like network of proteins that are associated with processes that maintain and change cell shape and produce cell movement in animal and bacterial cells. In plants, it is responsible for maintaining structures within the plant cell rather than the movement of entire cells. The cytoskeleton also forms tracks along which cellular organelles move, stimulated by contractile proteins attached to their various surfaces. Like a small highway infrastructure inside a cell. The cytoskeleton is formed by three types of filaments. Microfilaments are the thinnest and most abundant proteins of the cytoskeleton. They are composed of actin, a contractile protein, and can be assembled and disassembled quickly according to the needs of cell structure or organelles. Intermediate filaments are slightly larger in diameter and are most abundant in areas of cells that are stressed. Once these fibers are collected, they are not capable of rapid disassembly. Microtubules are hollow tubes made of a protein called tubulin. They are the thickest and stiffest of the threads. Microtubules are present in axons and long dendritic projections nerve cells. They can be quickly assembled and disassembled according to needs. Microtubules are structured around a cellular region called a centrosome, which surrounds two centrioles made up of 9 sets of fused microtubules. They are important during cell division, when the centrosome generates microtubular spindle fibers necessary for chromosome separation.
- The nucleus is at the center of most cells.
- The nucleus is the largest membrane-bound organelle.
- The nucleus is surrounded by a selective nuclear envelope.
Eukaryotic flagella have enough complex structure. They are thin cellular projections surrounded by three layers of membrane, containing 9 pairs of microtubules at the periphery and two in the center. They have a thickness of up to 0.1 millimeters and are capable of bending along the entire length. In addition to flagella, eukaryotes are characterized by the presence of cilia. They are identical in structure to flagella, differing only in size. The length of the cilia is no more than 0.01 millimeters.
He or she tells workers how much of each product to make and even hires and fires employees. A similar process occurs inside cells when we examine them under a microscope. animal cells, plant cells and mushrooms have a nucleus. However, there are no bacteria or viruses. Their bosses simply have a desk in the factory, not an office.
In this lesson we will look specifically at animal cells. Animal cells are eukaryotic, meaning they have a nucleus. They do not have a cell wall and are part of larger multicellular organisms, such as people. To understand what the nucleus does in a cell, let's first look at its structure.
Some prokaryotes also have flagella, however, they are very thin, about 20 nanometers in diameter. They are passively rotating hollow protein filaments.
4. Do all eukaryotic cells have a nucleus?
Answer. In eukaryotic organisms, all cells have a nucleus, with the exception of mature red blood cells of mammals and sieve tube cells of plants.
The nucleus has an outer barrier called the nuclear envelope or nuclear envelope surrounding it. Like an envelope surrounding a letter, a nuclear envelope contains all important information in the core. Nucleoplasm is a thick gel that fills inner part kernels. Inside the nucleoplasm are large structures called nucleoli. Nucleols are like tiny factories that make important parts of the cell called ribosomes. We'll look at this process later.
Since the core creates things, the core must send materials and products. The doors of the nucleus are called nuclear pores. Nuclear pores serve as gateways, selectively allowing things in and out of the nucleus. Because the nucleus contains so many important things, substances in the cell must have special tags so that they can enter the nucleus. Think of these special tags as key cards needed to enter a very important building. Now that we know what a kernel looks like, let's look at what it does for a cell.
5. What is the structure of the cell membrane?
Answer. Cell membrane is a membrane that separates the contents of the cell from external environment or neighboring cells. The basis of the cell membrane is a double layer of lipids, in which protein molecules are immersed, some of which function as receptors. The outside of the membrane is covered with a layer of glycoproteins - the glycocalyx.
Questions after §14
1. What is the structure of the cell membrane? What functions does it perform?
Answer. Each cell is covered with a plasma (cytoplasmic) membrane, which has a thickness of 8–12 nm. This membrane is built from two layers of lipids (bilipid layer, or bilayer). Each lipid molecule is formed by a hydrophilic head and a hydrophobic tail. IN biological membranes lipid molecules are arranged with their heads outward and their tails inward (toward each other). A double layer of lipids provides the barrier function of the membrane, preventing the contents of the cell from spreading and preventing the penetration of substances dangerous to it into the cell. Numerous protein molecules are immersed in the bilipid layer of the membrane. Some of them are on outside membranes, others - on the inner, and still others penetrate the entire membrane through and through. Membrane proteins perform whole line the most important functions. Some proteins are receptors with the help of which the cell perceives various influences on its surface. Other proteins form channels through which various ions are transported into and out of the cell. Third proteins are enzymes that ensure vital processes in the cell. As you already know, food particles cannot pass through the membrane; they enter the cell by phagocytosis or pinocytosis. Common name phago- and pinocytosis - endocytosis. There is also a process opposite to endocytosis - exocytosis, when substances synthesized in the cell (for example, hormones) are packaged into membrane vesicles that approach the cell membrane, are embedded in it, and the contents of the vesicle are released from the cell. In the same way, the cell can get rid of metabolic products it does not need.
2. What is the structure of the nuclear membrane?
Answer. The nucleus is separated from the cytoplasm by a shell consisting of two membranes. The inner membrane is smooth, and the outer membrane passes into the channels of the endoplasmic reticulum (ER). The total thickness of the double-membrane nuclear envelope is 30 nm. It has many pores through which mRNA and tRNA molecules exit the nucleus into the cytoplasm, and enzymes, ATP molecules, inorganic ions, etc. penetrate into the nucleus from the cytoplasm.
3. What is the function of the nucleus in a cell?
Answer. The nucleus contains all the information about the vital processes, growth and development of the cell. This information is stored in the nucleus in the form of DNA molecules that make up the chromosomes. Therefore, the nucleus coordinates and regulates protein synthesis, and consequently, all metabolic and energy processes occurring in the cell.
The role of the nucleus in a cell can be demonstrated in the following experiment. The amoeba cell is divided into two parts, one of which contains a nucleus, and the other, naturally, is without a nucleus. The first part quickly recovers from injury, feeds, grows, and begins to divide. The second part exists for several days and then dies. But if a nucleus from another amoeba is introduced into it, then it is quickly restored to normal body, which is capable of performing all the vital functions of an amoeba
4. What is chromatin?
Answer. Chromatin is DNA bound to proteins. Before cell division, DNA is tightly coiled to form chromosomes, and nuclear proteins - histones - are necessary for proper DNA folding, as a result of which the volume occupied by DNA is reduced many times over. When stretched, the length of a human chromosome can reach 5 cm.
5. How many DNA molecules form one chromosome?
Answer. The number of DNA molecules in a chromosome depends on the stage of the cell cycle.
Before DNA replication, a chromosome has one chromatid (i.e., one DNA molecule) and a set of chromosomes is described by the formula 2n2c (i.e., as many chromosomes are 2n, as many chromatids are 2c).
During the interphase, DNA replication occurs (chromatid doubling), and by the end of the interphase, the chromosomes become bichromatid and the set of chromosomes is described by the formula 2n4c (i.e. chromosomes - 2n, and chromatids are 2 times larger - 4c). Bichromatid chromosomes contain 2 DNA molecules.
In prophase and metaphase of mitosis, the chromosomes are bichromatid and the set of chromosomes is described by the formula 2n4c.
In anaphase, the chromatids move towards the poles and at each pole a diploid set of single-chromatid chromosomes 2n2c (at one pole) and 2n2c (at the other pole) is formed.
In telophase, a nuclear envelope is formed around the chromosomes; there are 2 nuclei in the cell, each of which contains a diploid set of single-chromatid chromosomes 2n2c (in one nucleus) and 2n2c (in another nucleus).
6. What function do the nucleoli perform?
Answer. Nucleoli - sections of DNA that are responsible for the synthesis of RNA molecules and proteins used by the cell to build ribosomes
7. Which cells have more than one nucleus, but several nuclei?
Answer. Multinucleated cells: skeletal muscle cells, striated muscle fibers, up to 20% of human liver cells, mice, stinging nettle, grape snail, tinder fungus, berry bug, coli, ciliate slipper.
8. Which cells do not have nuclei?
Answer. Prokaryotic cells do not have a nucleus. In eukaryotes, almost all cells have nuclei. The only exceptions are mammalian red blood cells and platelets.
).
Some cells do not have a nucleus in their mature state (for example, red blood cells in mammals and sieve tube cells in flowering plants).
The structure of the nucleus is the same in all eukaryotic cells (Fig. 1.16). The cell nucleus consists of a nuclear membrane, a nuclear matrix (nucleoplasm), chromatin and a nucleolus (one or more). Rice. 1.16 - . Core structure diagram: 1 - nucleolus; - 2 - chromatin; 3 - inner nuclear membrane;-4 7-outer nuclear membrane; 5
pores in the nuclear envelope; 6 ribosomes; rough endoplasmic reticulum. Chromatin on stained preparations, the cells represent a network of thin strands (fibrils), small granules or clumps. The basis of chromatin is made up of nucleoproteins - long thread-like DNA molecules (about 40%), connected to specific proteins - histones (40%). Chromatin also includes RNA, acidic proteins, lipids and
minerals (Ca 2- and Mg 2+ ions), as well as the enzyme DNA pol and merase, necessary for DNA replication. During nuclear division, nucleoproteins spiral, shorten, and as a result become denser and form into compact rod-shaped chromosomes, which become noticeable when observed under a light microscope. The number of chromosomes in mature germ cells is called haploid set and is designated by the letter l. Somatic cells contain double the number of chromosomes (diploid set), denoted as 2nd. Cells that have more than two sets of chromosomes are polyploid (4n, 8n
etc.). Paired chromosomes, i.e. identical in shape, structure and size, but having different origins(one maternal, the other paternal), are called homologous. The species specificity of the karyotype is characteristic. In human cells, the diploid set is 46 chromosomes, in the cells of soft wheat - 42, in potatoes - 18, in the house fly - 12, in the fruit fly Drosophila - 8. True, cells of different tissues of even one organism, depending on the function performed, can sometimes contain different number chromosomes. Thus, in animal liver cells there is a different number of sets of chromosomes (4l, 8h). For this reason, the concepts of mkaryotype and chromosome set are not entirely identical.
Some chromosomes have a secondary constriction that is not associated with the attachment of spindle threads. This region of the chromosome controls the synthesis of the nucleolus (nucleolar organizer).
Nucleoli - these are round, highly compacted areas not limited by a membrane cell nucleus with a diameter of 1-2 microns or more. The shape, size and number of nucleoli depend on functional state nuclei: the larger the nucleolus, the higher its activity.
The nucleoli contain about 80% protein, 10-15% RNA, 2-12% DNA. During nuclear division, the nucleoli are destroyed. At the end of cell division, nucleoli form again around certain regions of the chromosomes called nucleolar organizers. Ribosomal RNA genes are localized in nucleolar organizers. Here, ribosomal RNA is synthesized and combined with proteins, which leads to the formation of ribosomal subunits. The latter pass through pores in the nuclear membrane into the cytoplasm. Thus, the nucleolus is the site of rRNA synthesis and ribosome self-assembly.
Kernel functions the following:
- Storage and transmission of hereditary information in the form of an unchanged DNA structure.
- Control of cell vital processes through the formation of a protein synthesis apparatus (synthesis on DNA molecules different types RNA, formation of ribosomal subunits).
Source : ON THE. Lemeza L.V. Kamlyuk N.D. Lisov "A manual on biology for those entering universities"