In this article we will take a closer look at what plastids are. All autotrophic plants have basic cytoplasmic organelles called plastids. They got their name from the Greek - plastos, which translated into Russian means “fashioned”.

So what are plastids? What are their functions? You can find the answer to these questions by reading the article to the end. To begin with, let us highlight the main function of these organelles - the synthesis of organic substances. All plastids contain their own pigment, which determines their color. If we divide them according to this quality, we can name the following three groups:

• chloroplasts;
• chromoplasts;
• leukoplasts.

Meaning

Let's now find out what significance plastids have for plant life. Their importance in photosynthesis cannot be denied, but besides this, there are other important aspects. So, among them are:

• reduction of nitrite and sulfate;
• synthesis of metabolites (this includes purines, amino acids, fatty acids, and so on);
• synthesis of ABA, gibberellins, and so on (that is, regulatory molecules);
• storage function (iron, lipids, starch).

All plastids that are found in higher plants are diverse and each of them performs its own specific function. And their set directly depends on the type of cell.

Proplastids

We figured out what plastids are. Now let's move on to the characteristics of each individual species. First on our list were proplastids.

Compared to differentiated plastids, proplastids are smaller in size (up to 1 µm), their membrane system is poorly developed (fewer ribosomes). They have deposits of phytoferritin, the function of which is to store iron.

Leukoplasts

Plastids of this species have no color. Leukoplasts perform one very important function - storage. They are small in size and found in all plant cells. Thanks to leukoplasts, the following complex compounds are reproduced:

• starch;
• fats;
• proteins.

All of them are stored in different parts of the plant (tubers, fruits, seeds). These plastids are divided into three types based on the accumulation of substances:

• amyloplasts;
• proteinoplasts;
• eleoplasts.

In telling what plastids are, we will focus on the first type of leucoplasts.

Amyloplasts

All plastids are of great importance in biology. They are able to change from one species to another. A striking example is the transformation of leucoplasts into chloroplasts. The latter are green. Many have noticed that potato tubers turn green in the light, this is precisely due to the transition of leucoplasts to chloroplasts. Why do the leaves turn yellow in the fall? It's simple, chloroplasts turn into chromoplasts due to the destruction of chlorophyll in the first.

Externally, amyloplasts are similar to proplastids. They can transform into the following forms:

• chloroplasts;
• chromoplasts.

They can be found in the storage organs of plants.

Etioplasts

These plastids are usually called dark plastids. They are chloroplasts that lack the color of the sun. Many have noticed that flowers growing in the shade have a yellowish tint to the leaves. This indicates that the plant has a high concentration of etioplasts.

If a plant grown in sunlight is moved to the shade, then the chloroplasts will gradually begin to turn into etioplasts. The more of the latter, the cloudier and sicker the plant looks.

Chloroplasts

These plastids are the most popular in the plant world. Their color is green and their sizes reach 10 microns. The main function of chloroplasts is photosynthesis. Externally, this type of plastid looks like sacs or round bodies. They include:

• proteins;
• fats;
• pigments;

It is also important to note here that in different organisms the number, structure and size of these plastids differ.

Chromoplasts

The color of chromoplasts is slightly more varied. They can be yellow, orange, red.

This variety of colors is due to the accumulation of carotenoids. Thanks to the presence of these organelles in plants, we see a luxurious palette of colors in autumn trees, and we can distinguish ripened fruit (apples, tomatoes) from unripe ones. The shades of flower petals also depend on these organelles.

Chromoplasts can take on a variety of structures - circle, polygon, or have a needle shape.

Lecture No. 6.

Number of hours: 2

MITOCHONDRIA AND PLASTIDES

1.

2. Plastids, structure, varieties, functions

3.

Mitochondria and plastids are double-membrane organelles of eukaryotic cells. Mitochondria are found in all animal and plant cells. Plastids are characteristic of plant cells that carry out photosynthetic processes. These organelles have a similar structure and some common properties. However, in terms of basic metabolic processes they differ significantly from each other.

1. Mitochondria, structure, functional significance

General characteristics of mitochondria. Mitochondria (Greek “mitos” - thread, “chondrion” - grain, granule) are round, oval or rod-shaped double-membrane organelles with a diameter of about 0.2-1 microns and a length of up to 7-10 microns. These organellescan be detected using light microscopy because they are large and dense. The features of their internal structure can only be studied using an electron microscope.Mitochondria were discovered in 1894 by R. Altman, who gave them the name “bioblasts.”The term "mitochondrion" was introduced by K. Benda in 1897. Mitochondria are almost in all eukaryotic cells. Anaerobic organisms (intestinal amoebas, etc.) lack mitochondria. NumberThe number of mitochondria in a cell ranges from 1 to 100 thousand.and depends on the type, functional activity and age of the cell. Thus, in plant cells there are fewer mitochondria than in animal cells; and inmore in young cells than in old cells.The life cycle of mitochondria is several days. In a cell, mitochondria usually accumulate near areas of the cytoplasm where the need for ATP occurs. For example, in cardiac muscle, mitochondria are located near myofibrils, and in sperm they form a spiral sheath around the axis of the flagellum.

Ultramicroscopic structure of mitochondria. Mitochondria are bounded by two membranes, each of which is about 7 nm thick. The outer membrane is separated from the inner membrane by an intermembrane space about 10-20 nm wide. The outer membrane is smooth, and the inner one forms folds - cristae (Latin “crista” - ridge, outgrowth), increasing its surface. The number of cristae varies in the mitochondria of different cells. There can be from several dozen to several hundred. There are especially many cristae in the mitochondria of actively functioning cells, such as muscle cells. The cristae contain chains of electron transfer and associated phosphorylation of ADP (oxidative phosphorylation). The internal space of mitochondria is filled with a homogeneous substance called matrix. Mitochondrial cristae usually do not completely block the mitochondrial cavity. Therefore, the matrix is ​​continuous throughout. The matrix contains circular DNA molecules, mitochondrial ribosomes, and deposits of calcium and magnesium salts. The synthesis of RNA molecules of various types occurs on mitochondrial DNA; ribosomes are involved in the synthesis of a number of mitochondrial proteins. The small size of mitochondrial DNA does not allow encoding the synthesis of all mitochondrial proteins. Therefore, the synthesis of most mitochondrial proteins is under nuclear control and occurs in the cytoplasm of the cell. Without these proteins, the growth and functioning of mitochondria is impossible. Mitochondrial DNA encodes structural proteins responsible for the correct integration of individual functional components in mitochondrial membranes.

Reproduction of mitochondria. Mitochondria multiply by dividing by constriction or fragmentation of large mitochondria into smaller ones. Mitochondria formed in this way can grow and divide again.

Functions of mitochondria. The main function of mitochondria is to synthesize ATP. This process occurs as a result of the oxidation of organic substrates and the phosphorylation of ADP. The first stage of this process occurs in the cytoplasm under anaerobic conditions. Since the main substrate is glucose, the process is called glycolysis. At this stage, the substrate undergoes enzymatic breakdown to pyruvic acid with the simultaneous synthesis of a small amount of ATP. The second stage occurs in the mitochondria and requires the presence of oxygen. At this stage, further oxidation of pyruvic acid occurs with the release of CO 2 and the transfer of electrons to acceptors. These reactions are carried out using a number of enzymes of the tricarboxylic acid cycle, which are localized in the mitochondrial matrix. The electrons released during the oxidation process in the Krebs cycle are transferred to the respiratory chain (electron transport chain). In the respiratory chain, they combine with molecular oxygen to form water molecules. As a result, energy is released in small portions, which is stored in the form of ATP. The complete oxidation of one glucose molecule with the formation of carbon dioxide and water provides energy for the recharge of 38 ATP molecules (2 molecules in the cytoplasm and 36 in mitochondria).

Analogues of mitochondria in bacteria. Bacteria do not have mitochondria. Instead, they have electron transport chains located in the cell membrane.

2. Plastids, structure, varieties, functions. The problem of the origin of plastids

Plastids (from Greek. plastides– creating, forming) - These are double-membrane organelles characteristic of photosynthetic eukaryotic organisms.There are three main types of plastids: chloroplasts, chromoplasts and leucoplasts. The collection of plastids in a cell is called plastidome. Plastids are related to each other by a single origin in ontogenesis from proplastids of meristematic cells.Each of these types, under certain conditions, can transform into one another. Like mitochondria, plastids contain their own DNA molecules. Therefore, they are also able to reproduce independently of cell division.

Chloroplasts(from Greek "chloros" - green, "plastos" - fashioned)- These are plastids in which photosynthesis occurs.

General characteristics of chloroplasts. Chloroplasts are green organelles 5-10 µm long and 2-4 µm wide. Green algae have giant chloroplasts (chromatophores) reaching a length of 50 microns. In higher plants, chloroplasts have biconvex or ellipsoidal shape. The number of chloroplasts in a cell can vary from one (some green algae) to a thousand (shag). INOn average, the cell of higher plants contains 15-50 chloroplasts.Usually chloroplasts are evenly distributed throughout the cytoplasm of the cell, but sometimes they are grouped near the nucleus or cell membrane. Apparently, this depends on external influences (light intensity).

Ultramicroscopic structure of chloroplasts. Chloroplasts are separated from the cytoplasm by two membranes, each of which is about 7 nm thick. Between the membranes there is an intermembrane space with a diameter of about 20-30 nm. The outer membrane is smooth, the inner has a folded structure. Between the folds are located thylakoids, having the form of disks. Thylakoids form stacks like coins called grains. Mgrana are connected to each other by other thylakoids ( lamellas, frets). The number of thylakoids in one grana varies from a few to 50 or more. In turn, the chloroplast of higher plants contains about 50 grains (40-60), arranged in a checkerboard pattern. This arrangement ensures maximum illumination of each face. In the center of the grana is chlorophyll, surrounded by a layer of protein; then there is a layer of lipoids, again protein and chlorophyll. Chlorophyll has a complex chemical structure and exists in several modifications ( a, b, c, d ). Higher plants and algae contain x as the main pigmentlorophyll a with the formula C 55 H 72 O 5 N 4 M g . Contains chlorophyll as additional b (higher plants, green algae), chlorophyll c (brown and diatoms), chlorophyll d (red algae).The formation of chlorophyll occurs only in the presence of light and iron, which plays the role of a catalyst.The chloroplast matrix is ​​a colorless homogeneous substance that fills the space between the thylakoids.The matrix containsenzymes of the “dark phase” of photosynthesis, DNA, RNA, ribosomes.In addition, primary deposition of starch in the form of starch grains occurs in the matrix.

Properties of chloroplasts:

· semi-autonomy (they have their own protein synthesizing apparatus, but most of the genetic information is located in the nucleus);

· ability to move independently (move away from direct sunlight);

· ability to reproduce independently.

Reproduction of chloroplasts. Chloroplasts develop from proplastids, which are capable of replicating by fission. In higher plants, division of mature chloroplasts also occurs, but extremely rarely. As leaves and stems age and fruits ripen, chloroplasts lose their green color, turning into chromoplasts.

Functions of chloroplasts. The main function of chloroplasts is photosynthesis. In addition to photosynthesis, chloroplasts carry out the synthesis of ATP from ADP (phosphorylation), the synthesis of lipids, starch, and proteins. Chloroplasts also synthesize enzymes that provide the light phase of photosynthesis.

Chromoplasts(from Greek chromatos – color, paint and “ plastos " – fashioned)These are colored plastids. Their color is due to the presence of the following pigments: carotene (orange-yellow), lycopene (red) and xanthophyll (yellow). Chromoplasts are especially numerous in the cells of flower petals and fruit shells. Most chromoplasts are found in fruits and fading flowers and leaves. Chromoplasts can develop from chloroplasts, which lose chlorophyll and accumulate carotenoids. This happens when many fruits ripen: when filled with ripe juice, they turn yellow, pink or red.The main function of chromoplasts is to provide color to flowers, fruits, and seeds.

Unlike leucoplasts and especially chloroplasts, the inner membrane of chloroplasts does not form thylakoids (or forms single ones). Chromoplasts are the final result of plastid development (chloroplasts and plastids turn into chromoplasts).

Leukoplasts(from Greek leucos – white, plastos – fashioned, created). These are colorless plastidsround, ovoid, spindle-shaped. Found in the underground parts of plants, seeds, epidermis, and stem core. Especially rich leucoplasts of potato tubers.The inner shell forms a few thylakoids. In the light, chloroplasts are formed from chloroplasts.Leukoplasts in which secondary starch is synthesized and accumulated are called amyloplasts, oils – eylaloplasts, proteins – proteoplasts. The main function of leukoplasts is the accumulation of nutrients.

3. The problem of the origin of mitochondria and plastids. Relative autonomy

There are two main theories about the origin of mitochondria and plastids. These are the theories of direct filiation and sequential endosymbioses. According to the theory of direct filiation, mitochondria and plastids were formed through compartmentalization of the cell itself. Photosynthetic eukaryotes evolved from photosynthetic prokaryotes. In the resulting autotrophic eukaryotic cells, mitochondria were formed through intracellular differentiation. As a result of the loss of plastids, animals and fungi evolved from autotrophs.

The most substantiated theory is the theory of sequential endosymbioses. According to this theory, the emergence of a eukaryotic cell went through several stages of symbiosis with other cells. At the first stage, cells such as anaerobic heterotrophic bacteria included free-living aerobic bacteria, which turned into mitochondria. In parallel with this, in the prokaryotic host cell the genophore is formed into a nucleus isolated from the cytoplasm. In this way, the first eukaryotic cell, which was heterotrophic, arose. The emerging eukaryotic cells, through repeated symbioses, included blue-green algae, which led to the appearance of chloroplast-type structures in them. Thus, heterotrophic eukaryotic cells already had mitochondria when the latter acquired plastids as a result of symbiosis. Subsequently, as a result of natural selection, mitochondria and chloroplasts lost part of their genetic material and turned into structures with limited autonomy.

Evidence for the endosymbiotic theory:

1. The similarity of structure and energy processes in bacteria and mitochondria, on the one hand, and in blue-green algae and chloroplasts, on the other hand.

2. Mitochondria and plastids have their owna specific protein synthesis system (DNA, RNA, ribosomes). The specificity of this system lies in its autonomy and sharp difference from that in a cell.

3. The DNA of mitochondria and plastids issmall cyclic or linear molecule,which differs from the DNA of the nucleus and in its characteristics approaches the DNA of prokaryotic cells.DNA synthesis of mitochondria and plastids is notdepends on nuclear DNA synthesis.

4. Mitochondria and chloroplasts contain i-RNA, t-RNA, and r-RNA. The ribosomes and rRNA of these organelles differ sharply from those in the cytoplasm. In particular, the ribosomes of mitochondria and chloroplasts, unlike cytoplasmic ribosomes, are sensitive to the antibiotic chloramphenicol, which suppresses protein synthesis in prokaryotic cells.

5. The increase in the number of mitochondria occurs through the growth and division of the original mitochondria. An increase in the number of chloroplasts occurs through changes in proplastids, which, in turn, multiply by division.

This theory well explains the preservation of remnants of replication systems in mitochondria and plastids and allows us to construct a consistent phylogeny from prokaryotes to eukaryotes.

Relative autonomy of chloroplasts and plastids. In some respects, mitochondria and chloroplasts behave like autonomous organisms. For example, these structures are formed only from the original mitochondria and chloroplasts. This was demonstrated in experiments on plant cells, in which the formation of chloroplasts was suppressed by the antibiotic streptomycin, and on yeast cells, where the formation of mitochondria was suppressed by other drugs. After such effects, the cells never restored the missing organelles. The reason is that mitochondria and chloroplasts contain a certain amount of their own genetic material (DNA) that codes for part of their structure. If this DNA is lost, which is what happens when organelle formation is suppressed, then the structure cannot be recreated. Both types of organelles have their own protein-synthesizing system (ribosomes and transfer RNAs), which is somewhat different from the main protein-synthesizing system of the cell; it is known, for example, that the protein-synthesizing system of organelles can be suppressed with the help of antibiotics, while they have no effect on the main system. Organelle DNA is responsible for the bulk of extrachromosomal, or cytoplasmic, inheritance. Extrachromosomal heredity does not obey Mendelian laws, since when a cell divides, the DNA of organelles is transmitted to daughter cells in a different way than chromosomes. The study of mutations that occur in organelle DNA and chromosomal DNA has shown that organelle DNA is responsible for only a small part of the structure of organelles; most of their proteins are encoded in genes located on chromosomes. The relative autonomy of mitochondria and plastids is considered as one of the evidence of their symbiotic origin.

Plastid structure: 1 - outer membrane; 2 - internal membrane; 3 - stroma; 4 - thylakoid; 5 - grain; 6 - lamellae; 7 - starch grains; 8 - lipid drops.

Plastids are characteristic only of plant cells. Distinguish three main types of plastids: leucoplasts are colorless plastids in the cells of uncolored parts of plants, chromoplasts are colored plastids usually yellow, red and orange, chloroplasts are green plastids.

Chloroplasts. In the cells of higher plants, chloroplasts have the shape of a biconvex lens. The length of chloroplasts ranges from 5 to 10 µm, diameter - from 2 to 4 µm. Chloroplasts are bounded by two membranes. The outer membrane (1) is smooth, the inner (2) has a complex folded structure. The smallest fold is called thylakoid(4). A group of thylakoids arranged like a stack of coins is called facet(5). The chloroplast contains on average 40–60 grains, arranged in a checkerboard pattern. The granae are connected to each other by flattened channels - lamellae(6). The thylakoid membranes contain photosynthetic pigments and enzymes that provide ATP synthesis. The main photosynthetic pigment is chlorophyll, which determines the green color of chloroplasts.

The interior space of the chloroplasts is filled stroma(3). The stroma contains circular “naked” DNA, 70S-type ribosomes, Calvin cycle enzymes, and starch grains (7). Inside each thylakoid there is a proton reservoir, and H + accumulates. Chloroplasts, like mitochondria, are capable of autonomous reproduction by dividing into two. They are found in the cells of the green parts of higher plants, especially many chloroplasts in leaves and green fruits. Chloroplasts of lower plants are called chromatophores.

Function of chloroplasts: photosynthesis. It is believed that chloroplasts originated from ancient endosymbiotic cyanobacteria (symbiogenesis theory). The basis for this assumption is the similarity of chloroplasts and modern bacteria in a number of characteristics (circular, “naked” DNA, 70S-type ribosomes, method of reproduction).

Leukoplasts. The shape varies (spherical, round, cupped, etc.). Leukoplasts are bounded by two membranes. The outer membrane is smooth, the inner one forms few thylakoids. The stroma contains circular “naked” DNA, 70S-type ribosomes, enzymes for the synthesis and hydrolysis of reserve nutrients. There are no pigments. The cells of the underground organs of the plant (roots, tubers, rhizomes, etc.) have especially many leucoplasts. Function of leucoplasts: synthesis, accumulation and storage of reserve nutrients. Amyloplasts- leukoplasts that synthesize and accumulate starch, elaioplasts- oils, proteinoplasts- proteins. Different substances can accumulate in the same leukoplast.

Chromoplasts. Bounded by two membranes. The outer membrane is smooth, the inner membrane is either smooth or forms single thylakoids. The stroma contains circular DNA and pigments - carotenoids, which give chromoplasts a yellow, red or orange color. The form of accumulation of pigments is different: in the form of crystals, dissolved in lipid droplets (8), etc. Contained in the cells of mature fruits, petals, autumn leaves, and rarely in root vegetables. Chromoplasts are considered the final stage of plastid development.

Function of chromoplasts: coloring flowers and fruits and thereby attracting pollinators and seed dispersers.

All types of plastids can be formed from proplastids. Proplastids- small organelles contained in meristematic tissues. Since plastids have a common origin, interconversions between them are possible. Leukoplasts can turn into chloroplasts (greening of potato tubers in the light), chloroplasts - into chromoplasts (yellowing of leaves and reddening of fruits). The transformation of chromoplasts into leucoplasts or chloroplasts is considered impossible.

Chloroplasts are green plastids of higher plants containing chlorophyll, a photosynthetic pigment. They are round bodies measuring from 4 to 10 microns. Chemical composition of the chloroplast: approximately 50% protein, 35% fat, 7% pigments, a small amount of DNA and RNA. Representatives of different groups of plants have a different complex of pigments that determine color and take part in photosynthesis. These are subtypes of chlorophyll and carotenoids (xanthophyll and carotene). When viewed under a light microscope, the granular structure of plastids is visible - these are grana. Under an electron microscope, small transparent flattened sacs (cisterns, or grana) are observed, formed by a protein-lipid membrane and located directly in the stroma. Moreover, some of them are grouped in packs similar to columns of coins (gran thylakoids), others, larger ones, are located between the thylakoids. Thanks to this structure, the active synthesizing surface of the lipid-protein-pigment gran complex, in which photosynthesis occurs in the light, increases.
Chromoplasts
Leukoplasts They are colorless plastids whose main function is usually storage. The sizes of these organelles are relatively small. They are round or slightly oblong in shape and are characteristic of all living plant cells. In leucoplasts, the synthesis from simple compounds of more complex ones is carried out - starch, fats, proteins, which are stored in reserve in tubers, roots, seeds, fruits. Under an electron microscope, it is noticeable that each leucoplast is covered with a two-layer membrane, in the stroma there is only one or a small number of membrane outgrowths, the main space is filled with organic substances. Depending on what substances accumulate in the stroma, leukoplasts are divided into amyloplasts, proteinoplasts and eleoplasts.

74. What is the structure of the nucleus and its role in the cell? What structures of the nucleus determine its functions? What is chromatin?

The nucleus is the main component of the cell that carries genetic information. The nucleus is located in the center. The shape varies, but is always round or oval. Sizes vary. The contents of the kernel are liquid in consistency. There are membrane, chromatin, karyolymph (nuclear juice), and nucleolus. The nuclear envelope consists of 2 membranes separated by a perinuclear space. The shell is equipped with pores through which large molecules of various substances are exchanged. It can be in 2 states: rest - interphase and division - mitosis or meiosis.

The nucleus carries out two groups of general functions: one associated with the storage of genetic information itself, the other with its implementation, ensuring protein synthesis.

The first group includes processes associated with maintaining hereditary information in the form of an unchanged DNA structure. These processes are associated with the presence of so-called repair enzymes that eliminate spontaneous damage to the DNA molecule (break of one of the DNA chains, part of the radiation damage), which preserves the structure of DNA molecules practically unchanged over generations of cells or organisms. Further, reproduction or reduplication of DNA molecules occurs in the nucleus, which makes it possible for two cells to receive exactly the same volumes of genetic information, both qualitatively and quantitatively. Processes of change and recombination of genetic material occur in the nuclei, which is observed during meiosis (crossing over). Finally, nuclei are directly involved in the distribution of DNA molecules during cell division.

Another group of cellular processes ensured by the activity of the nucleus is the creation of the protein synthesis apparatus itself. This is not only the synthesis, transcription on DNA molecules of various messenger RNAs and ribosomal RNAs. In the nucleus of eukaryotes, the formation of ribosomal subunits also occurs by complexing ribosomal RNA synthesized in the nucleolus with ribosomal proteins, which are synthesized in the cytoplasm and transferred to the nucleus.

Thus, the nucleus is not only the reservoir of genetic material, but also the place where this material functions and reproduces. Therefore, loss of hair and disruption of any of the above functions is detrimental to the cell as a whole. Thus, disruption of repair processes will lead to a change in the primary structure of DNA and automatically to a change in the structure of proteins, which will certainly affect their specific activity, which may simply disappear or change in such a way that it will not provide cellular functions, as a result of which the cell dies. Disturbances in DNA replication will lead to a stop in cell reproduction or to the appearance of cells with an incomplete set of genetic information, which is also detrimental to cells. A disruption in the distribution of genetic material (DNA molecules) during cell division will lead to the same result. Loss as a result of damage to the nucleus or in the event of violations of any regulatory processes in the synthesis of any form of RNA will automatically lead to a stop in protein synthesis in the cell or to its gross disturbances.
Chromatin(Greek χρώματα - colors, paints) - this is the substance of chromosomes - a complex of DNA, RNA and proteins. Chromatin is found inside the nucleus of eukaryotic cells and is part of the nucleoid in prokaryotes. It is in the composition of chromatin that genetic information is realized, as well as DNA replication and repair.

75. What is the structure and types of chromosomes? What is a karyotype, autosomes, heterosomes, diploid and haploid sets of chromosomes?

Chromosomes are organelles of the cell nucleus, the totality of which determines the basic hereditary properties of cells and organisms. The complete set of chromosomes in a cell, characteristic of a given organism, is called a karyotype. In any cell of the body of most animals and plants, each chromosome is represented twice: one of them is received from the father, the other from the mother during the fusion of the nuclei of germ cells during the process of fertilization. Such chromosomes are called homologous, and a set of homologous chromosomes is called diploid. In the chromosome set of cells of dioecious organisms there is a pair (or several pairs) of sex chromosomes, which, as a rule, differ in different sexes in morphological characteristics; the remaining chromosomes are called autosomes. In mammals, genes that determine the sex of the organism are located on the sex chromosomes.
The importance of chromosomes as cellular organelles responsible for the storage, reproduction and implementation of hereditary information is determined by the properties of the biopolymers that make up their composition.
Autosomes In living organisms with chromosomal sex determination, paired chromosomes are called identical in male and female organisms. In other words, except for sex chromosomes, all other chromosomes in dioecious organisms will be autosomes.
Autosomes are designated by serial numbers. Thus, a person has 46 chromosomes in the diploid set, of which 44 autosomes (22 pairs, designated by numbers 1 to 22) and one pair of sex chromosomes (XX in women and XY in men).
Haploid set of chromosomes Let's start with the haploid set. It is a collection of completely different chromosomes, i.e. in a haploid organism there are several of these nucleoprotein structures, unlike each other (photo). The haploid set of chromosomes is characteristic of plants, algae and fungi. Diploid set of chromosomes This set is a collection of chromosomes in which each of them has a double, i.e. these nucleoprotein structures are arranged in pairs (photo). A diploid set of chromosomes is characteristic of all animals, including humans. By the way, about the last one. A healthy person has 46 of them, i.e. 23 pairs. However, its gender is determined by only two, called sexual ones - X and Y. Read more on SYL.ru:

76. Define the cell cycle and characterize its phases. What functions of life are provided by cell division?

Cell cycle- this is the period of existence of a cell from the moment of its formation by dividing the mother cell until its own division or death.

The eukaryotic cell cycle consists of two periods:
1The period of cell growth, called “interphase,” during which DNA and proteins are synthesized and preparation for cell division occurs.

2The period of cell division, called “phase M” (from the word mitosis - mitosis).

Cell division. The growth of an organism occurs through the division of its cells. The ability to divide is the most important property of cellular life. 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.

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Plastids

Plastids are the main cytoplasmic organelles of autotrophic plant cells. The name comes from the Greek word “plastos”, which means “fashioned”.

The main function of plastids is the synthesis of organic substances, due to the presence of their own DNA and RNA and protein synthesis structures. Plastids also contain pigments that give them color. All types of these organelles have a complex internal structure. The outside of the plastid is covered by two elementary membranes; there is a system of internal membranes immersed in the stroma or matrix.

Classification of plastids by color and function involves dividing these organelles into three types: chloroplasts, leucoplasts and chromoplasts. Algae plastids are called chromatophores.

Chloroplasts are green plastids of higher plants containing chlorophyll, a photosynthetic pigment. They are round bodies measuring from 4 to 10 microns. Chemical composition of the chloroplast: approximately 50% protein, 35% fat, 7% pigments, a small amount of DNA and RNA. Representatives of different groups of plants have a different complex of pigments that determine color and take part in photosynthesis. These are subtypes of chlorophyll and carotenoids (xanthophyll and carotene). When viewed under a light microscope, the granular structure of plastids is visible - these are grana. Under an electron microscope, small transparent flattened sacs (cisterns, or grana) are observed, formed by a protein-lipid membrane and located directly in the stroma.

Moreover, some of them are grouped in packs similar to columns of coins (gran thylakoids), others, larger ones, are located between the thylakoids. Thanks to this structure, the active synthesizing surface of the lipid-protein-pigment gran complex, in which photosynthesis occurs in the light, increases.

Chromoplasts- plastids, the color of which is yellow, orange or red, which is due to the accumulation of carotenoids in them. Due to the presence of chromoplasts, autumn leaves, flower petals, and ripe fruits (tomatoes, apples) have a characteristic color. These organelles can be of various shapes - round, polygonal, sometimes needle-shaped.

Leukoplasts They are colorless plastids whose main function is usually storage. The sizes of these organelles are relatively small.

They are round or slightly oblong in shape and are characteristic of all living plant cells. In leucoplasts, the synthesis from simple compounds of more complex ones is carried out - starch, fats, proteins, which are stored in reserve in tubers, roots, seeds, fruits. Under an electron microscope, it is noticeable that each leucoplast is covered with a two-layer membrane, in the stroma there is only one or a small number of membrane outgrowths, the main space is filled with organic substances. Depending on what substances accumulate in the stroma, leukoplasts are divided into amyloplasts, proteinoplasts and eleoplasts.

All types of plastids have a common origin and are capable of changing from one type to another. Thus, the transformation of leucoplasts into chloroplasts is observed when potato tubers turn green in the light, and in the autumn, chlorophyll is destroyed in the chloroplasts of green leaves, and they are transformed into chromoplasts, which is manifested by yellowing of the leaves. Each specific plant cell can contain only one type of plastid.

Plastids are organelles of plant cells and some photosynthetic protozoa. Animals and fungi do not have plastids.

Plastids are divided into several types. The most important and well-known is the chloroplast, which contains the green pigment chlorophyll, which ensures the process of photosynthesis.

Other types of plastids are multi-colored chromoplasts and colorless leucoplasts. Amyloplasts, lipidoplasts, and proteinoplasts are also distinguished, which are often considered types of leucoplasts.

All types of plastids are related to each other by a common origin or possible interconversion. Plastids develop from proplastids - smaller organelles of meristematic cells.

The structure of plastids

Most plastids are double-membrane organelles; they have an outer and an inner membrane.

However, there are organisms whose plastids have four membranes, which is due to the characteristics of their origin.

In many plastids, especially in chloroplasts, the internal membrane system is well developed, forming such structures as thylakoids, grana (stacks of thylakoids), lamellae - elongated thylakoids connecting neighboring grana. The internal contents of plastids are usually called stroma. Among other things, it contains starch grains.

It is believed that in the process of evolution, plastids appeared in a similar way to mitochondria - by introducing another prokaryotic cell into the host cell, which in this case is capable of photosynthesis. Therefore, plastids are considered semi-autonomous organelles. They can divide regardless of cell divisions; they have their own DNA, RNA, prokaryotic-type ribosomes, i.e., their own protein synthesizing apparatus. This does not mean that plastids do not receive proteins and RNA from the cytoplasm. Some of the genes that control their functioning are located in the nucleus.

Functions of plastids

The functions of plastids depend on their type. Chloroplasts perform a photosynthetic function. Leukoplasts accumulate reserve nutrients: starch in amyloplasts, fats in elaioplasts (lipidoplasts), proteins in proteinoplasts.

Chromoplasts, due to the carotenoid pigments they contain, color various parts of plants - flowers, fruits, roots, autumn leaves, etc. Bright color often serves as a kind of signal for pollinating animals and distributors of fruits and seeds.

In the degenerating green parts of plants, chloroplasts transform into chromoplasts. The chlorophyll pigment is destroyed, so the remaining pigments, despite the small amount, become noticeable in the plastids and color the foliage in yellow-red shades.

Plastids are organelles of plant cells. One type of plastid is photosynthetic chloroplasts. Other common varieties are chromoplasts and leucoplasts. All of them are united by a unity of origin and a general structural plan. Distinguishes between the predominance of certain pigments and the functions performed.

Plastids develop from proplastids, which are present in the cells of the educational tissue and are significantly smaller in size than the mature organelle. In addition, plastids are capable of dividing in two by constriction, which is similar to the division of bacteria.

In the structure of plastids, there are outer and inner membranes, the internal contents are stroma, an internal membrane system, which is especially developed in chloroplasts, where it forms thylakoids, grana and lamellae.

The stroma contains DNA, ribosomes, and various types of RNA. Thus, like mitochondria, plastids are capable of independently synthesizing some of the necessary protein molecules. It is believed that in the process of evolution, plastids and mitochondria appeared as a result of the symbiosis of different prokaryotic organisms, one of which became the host cell, and the others became its organelles.

The functions of plastids depend on their type:

• chloroplasts→ photosynthesis,
• chromoplasts→ coloring of plant parts,
• leucoplasts→ supply of nutrients.

Plant cells contain predominantly one type of plastid. Chloroplasts are dominated by the pigment chlorophyll, which is why the cells containing them are green. Chromoplasts contain carotenoid pigments, which give colors from yellow through orange to red.

Leucoplasts are colorless.

The bright colors of the flowers and fruits of the plant with chromoplasts attract pollinating insects and seed-dispersing animals. In autumn leaves, chlorophyll is destroyed, resulting in color determined by carotenoids. Because of this, the foliage acquires the appropriate color. In this case, chloroplasts turn into chromoplasts, which are often considered as the final stage of plastid development.

When exposed to light, leukoplasts can transform into chloroplasts. This can be observed in potato tubers when they begin to turn green in the light.

There are several types of leukoplasts depending on the type of substances accumulated in them:

• proteinoplasts→ proteins,
• elaioplasts, or lipidoplasts, → fats,
• amyloplasts→ carbohydrates, usually in the form of starch.

Plastids are the main cytoplasmic organelles of autotrophic plant cells. The name comes from the Greek word “plastos”, which means “fashioned”.

The main function of plastids is the synthesis of organic substances, due to the presence of their own DNA and RNA and protein synthesis structures. Plastids also contain pigments that give them color. All types of these organelles have a complex internal structure. The outside of the plastid is covered by two elementary membranes; there is a system of internal membranes immersed in the stroma or matrix.

Classification of plastids by color and function involves dividing these organelles into three types: chloroplasts, leucoplasts and chromoplasts. Algae plastids are called chromatophores.

These are green plastids of higher plants containing chlorophyll, a photosynthetic pigment. They are round-shaped bodies ranging in size from 4 to 10 microns. Chemical composition of the chloroplast: approximately 50% protein, 35% fat, 7% pigments, a small amount of DNA and RNA. Representatives of different groups of plants have a different complex of pigments that determine color and take part in photosynthesis. These are subtypes of chlorophyll and carotenoids (xanthophyll and carotene).

When viewed under a light microscope, the granular structure of plastids is visible - these are grana. Under an electron microscope, small transparent flattened sacs (cisterns, or grana) are observed, formed by a protein-lipid membrane and located directly in the stroma. Moreover, some of them are grouped in packs similar to columns of coins (gran thylakoids), others, larger ones, are located between the thylakoids. Thanks to this structure, the active synthesizing surface of the grana lipid-protein-pigment complex, in which photosynthesis occurs in the light, increases.

These are plastids whose color is yellow, orange or red, which is due to the accumulation of carotenoids in them. Due to the presence of chromoplasts, autumn leaves, flower petals, and ripe fruits (tomatoes, apples) have a characteristic color. These organelles can be of various shapes - round, polygonal, sometimes needle-shaped.

Leukoplasts

They are colorless plastids, the main function of which is usually storage. The sizes of these organelles are relatively small. They are round or slightly oblong in shape and are characteristic of all living plant cells. In leucoplasts, the synthesis from simple compounds of more complex ones is carried out - starch, fats, proteins, which are stored in reserve in tubers, roots, seeds, fruits. Under an electron microscope, it is noticeable that each leucoplast is covered with a two-layer membrane, in the stroma there is only one or a small number of membrane outgrowths, the main space is filled with organic substances. Depending on what substances accumulate in the stroma, leukoplasts are divided into amyloplasts, proteinoplasts and eleoplasts.