Lysosomes are membrane organelles with a diameter of 0.2 to 2.0 µm. They are part of the eukaryotic cell, where hundreds of lysosomes are located. Their main task is intracellular digestion (breakdown of biopolymers); for this, the organelles have a special set of hydrolytic enzymes (about 60 types are known today). Enzyme substances are surrounded by a closed membrane, which prevents their penetration into the cell and its destruction.

The first to identify lysosomes and begin to study them was the Belgian scientist in the field of biochemistry, Christian de Duve, back in 1955.

Features of the structure of lysosomes

Lysosomes look like membrane sacs with acidic contents. The configuration is oval or round. All cells of the body contain lysosomes, with the exception of red blood cells.

A special difference between lysosomes and other organelles is the presence of acid hydrolases in the internal environment. They ensure the breakdown of protein substances, fats, carbohydrates, and nucleic acids.

Lysosomal enzymes include phosphatases (marker enzyme), sulfatase, phospholipase and many others. The optimal environment for normal functioning of organelles is acidic (pH = 4.5 - 5). If enzymes are insufficient or their activity is ineffective, or the internal environment is alkalized, lysosomal storage diseases (glycogenosis, mucopolysaccharidosis, Gaucher disease, Tay-Sachs disease) may occur. As a result, undigested substances accumulate in the cell: glycoproteins, lipids, etc.

The single-membrane membrane of lysosomes is equipped with transport proteins that ensure the transfer of digestion products from the organelle to the internal environment of the cell.

Are there lysosomes in a plant cell?

No. Plant cells contain vacuoles - formations filled with juice and enclosed in a membrane. They are formed from provacuoles that move away from the EPS and. Cell vacuoles perform a number of important functions: accumulation of nutrients, maintenance of turgor, digestion of organic substances (which indicates similarities between plant vacuoles and lysosomes).

Where are lysosomes formed?

The formation of lysosomes occurs from vesicles that bud from the Golgi apparatus. The formation of organelles also requires the participation of the granular membrane of the endoplasmic reticulum. All lysosomal enzymes are synthesized by ER ribosomes and then sent to the Golgi apparatus.

Types of lysosomes

There are two types of lysosomes. Primary lysosomes are formed near the Golgi apparatus and contain unactivated enzymes.

Secondary lysosomes, or phagosomes have activated enzymes that directly interact with the broken down biopolymers. As a rule, lysosomal enzymes are activated when the pH changes to the acidic side.

Lysosomes are also divided into:

• heterolysosomes- digestive substances captured by the cell by phagocytosis (solid particles) or pinocytosis (liquid absorption);
• autolysosomes- designed to destroy their own intracellular structures.

Functions of lysosomes in the cell

• Intracellular digestion;
• autophagocytosis;
• autolysis

Intracellular digestion Nutrient compounds or foreign agents (bacteria, viruses, etc.) that enter the cell during endocytosis are carried out under the action of lysosomal enzymes.

After digestion of the captured material, the breakdown products enter the cytoplasm, undigested particles remain inside the organelle, which is now called - residual body. Under normal conditions, the bodies leave the cell. In nerve cells that have a long life cycle, during the period of their existence many residual bodies accumulate, which contain the pigment of aging (they are also not excreted during the development of pathology).

Autophagocytosis- splitting of cellular structures that are no longer needed, for example, during the formation of new organelles; the cell gets rid of old ones by autophagocytosis.

Autolysis- self-destruction of the cell, which leads to its destruction. This process is not always pathological in nature, but occurs under normal conditions of development of the individual or during the differentiation of individual cells.

For example: cell death is a natural process for a normally functioning organism, therefore there is a programmed cell death - apoptosis. The role of lysosomes in apoptosis is quite large: hydrolytic enzymes digest dead cells and cleanse the body of those that have already fulfilled their function.

When a tadpole transforms into a mature individual, lysosomes located in the cells of the tail part break it down, as a result the tail disappears, and the digestion products are absorbed by the rest of the body cells.

Summary table of the structure and functions of lysosomes

Even from elementary school, a person understands: everything that surrounds him consists of tiny particles - cells. These designer parts are very small, which makes it impossible for us to see them with the naked eye. But modern technology can help us with this.

Microscopes, which children get acquainted with at school, can show us the whole, previously unexplored world. But a cell is not the smallest unit, because it contains a mass of organelles, the sizes of which are much smaller. Today we will look at the structure and function of lysosomes. The latter is also part of cells (animal and plant).

Lysosomes

Next, we will understand what the structure and function of lysosomes are. The main thing you need to understand is what the component part of a cell looks like. That is, a lysosome is an organelle. You can put it another way: this organelle is a cellular structure. What else do you need to know about the lysosome? All of them, regardless of type, contain a large number of enzymes, of which there are about forty. They are needed to break down through hydrolysis:

• proteins;
• polysaccharides;
• nucleic acids.

Substances can enter the cell in the following ways:

• phagocytosis;
• pinocytosis.

Lysosomes help cells digest nutrients, that is, they carry out intracellular digestion. They are capable of breaking down substances through hydrolysis into the smallest particles, which can easily penetrate the membrane into the internal environment of the cell. The resulting elements do not disappear without a trace, but participate in other, no less important processes, for example, in the creation of new organelles.

Here we should also note that some plant cells may contain only 1 or 2 lysosomes, but their sizes are much larger than those found in animal cells. If we consider the percentage of organelles, then lysosomes occupy no more than five percent. In animal cells their number can reach several thousand.

Structure

The structure and function of lysosomes is a rather interesting topic. In this section you will learn:

• what these organelles consist of;
• their sizes;
• varieties.

We suggest you start immediately. Lysosomes consist of an internal part that contains enzymes and membranes, which can collapse and release their particles into the cell space, where they are deactivated. Their size is extremely small, approximately 0.2 microns, which is why lysosomes can be found in such large numbers in the cell.

The following types of these organelles are distinguished:

• primary;
• secondary;
• residual bodies.

The life cycle of a lysosome looks approximately as follows: primary lysosomes are formed in the Golgi apparatus, they capture waste organelles and move into the secondary phase, and after digestion, residual bodies are formed that are used by the cell.

Education

We looked at the features of the structure and functions of lysosomes. Now let's move on to the formation of these organelles. We offer a brief and clear look at this process. Primary lysosomes are formed in the Golgi apparatus. Their sizes are so small that these organelles are difficult to distinguish from vacuoles. Inside you can find a structureless substance, and in appearance they appear to be bubbles. Secondary lysosomes are formed by the fusion of primary ones with vacuoles of any type:

• phagocytic;
• pinocytic.

Thus, digestive vacuoles are formed that are capable of digesting substrates. Sometimes these organelles merge with each other and form elements that are more complex in structure. Substances that enter the lysosome are broken down into monomers, then they pass through the membrane and are involved in metabolic processes. But digestion may not be complete. In this case, secondary lysosomes transform into residual bodies. They contain fewer enzymes, their contents become compacted, and reprocessing begins.

These organelles are present in almost all cells, but there are also specialized ones, where their number is much higher (leukocytes). Some plant cells lack lysosomes, but they contain vacuoles with the necessary enzymes, and they perform their functions.

Functions

After we have found out what the structure and functions of lysosomes are, let's move on to the second part of this question. Now we will list the main functions of these organelles and give a brief description.

Digestion

We looked at lysosomes. The structure and functions have been briefly described in the previous sections. Now we suggest learning a little more about intracellular digestion and the role these organelles play. Many animals have intracellular digestion. Lysosomes help this process by capturing and digesting food. In this case, capture occurs by the endocytic method.

Autolysis

Considering the structural features of the lysosome and its functions, we mentioned the process of autolysis, in which lysosomes are directly involved. We have already looked at this function using the example of a frog. Now let's talk about how this happens.

The lysosome membrane may collapse. If this happens to all organelles, the cell will die. This is how autolysis occurs. That is, self-destruction.

Autophagy

This function is necessary for the cell to renew its organelles. Lysosomes capture waste structures and break them down. The destroyed organelles are replaced by new ones, the components of which are compounds formed as a result of autophagy.

Prevalence among living kingdoms

Lysosomes were first described in 1955 by Christian de Duve in animal cells, and were later discovered in plant cells. In plants, vacuoles are similar to lysosomes in the method of formation, and partly in function. Lysosomes are also present in most protists (both with phagotrophic and osmotrophic types of nutrition) and in fungi. Thus, the presence of lysosomes is characteristic of cells of all eukaryotes. Prokaryotes do not have lysosomes because they lack phagocytosis and do not have intracellular digestion.

Signs of lysosomes

One of the characteristics of lysosomes is the presence in them of a number of enzymes (acid hydrolases) capable of breaking down proteins, carbohydrates, lipids and nucleic acids. Lysosome enzymes include cathepsins (tissue proteases), acid ribonuclease, phospholipase, etc. In addition, lysosomes contain enzymes that are capable of removing sulfate (sulfatases) or phosphate (acid phosphatase) groups from organic molecules.

see also

Links

• Molecular Biology Of The Cell, 4th edition, 2002 - textbook on molecular biology in English

Golgi complex, or Golgi apparatus , - These are single-membrane organelles of eukaryotic cells, the main functions of which are the storage and removal of excess substances from the cells of the body and the formation of lysosomes. These organelles were discovered in 1898 by the Italian physicist C. Golgi.

Structure . Constructed from bags called tanks, tube system And bubbles various sizes. The cisternae of the Golgi complex (CG) are also polar: vesicles with substances that detach from the ER (formation zone) approach one pole, and vesicles with substances separate from the other pole (maturation zone). In cells, the Golgi complex is located mainly near the nucleus. CG is present in all eukaryotic cells, but its structure may differ in different organisms. Thus, in plant cells there are several structural units called dictyosomes. Membranes of the Golgi complex are synthesized granular EPS, adjacent to it. During cell division, the CG breaks down into separate structural units, which are randomly distributed between daughter cells.

Functions . The Golgi complex performs quite diverse and important functions related to the formation and transformation of complex substances. Here are some of them:

1) participation in the construction of biological membranes - for example, in protozoan cells, with the help of its elements, contractile vacuoles, is formed in the sperm acrosomsa;

2 ) formation of lysosomes- hydrolase enzymes synthesized in EPS are packaged into a membrane vesicle, which is separated into the cytoplasm;

3) peroxisome formation- bodies with the catalase enzyme are formed to destroy hydrogen peroxide, which is formed during the oxidation of organic substances and is a toxic composition for cells;

4) synthesis of surface apparatus compounds- lipo-, glyco-, and mucoproteins are formed, which are part of the glycocalyx, cell walls, and mucous capsules;

5) participation in the secretion of substances from the cell- in the CG, the maturation of secretory granules into vesicles occurs, and the movement of these vesicles in the direction of the plasma membrane.

Lysosomes, structure and functions

Lysosomes (from Greek Lysis - dissolution, soma - body) - These are single-membrane organelles of eukaryotic cells that look like round bodies. In unicellular organisms their role is intracellular digestion, in multicellular organisms they perform the function of breaking down substances foreign to the cell. Lysosomes can be located anywhere in the cytoplasm. Lysosomes were discovered by the Belgian cytologist Christian de Duve in 1949.

Structure . Lysosomes have the form of vesicles with a diameter of about 0.5 microns, surrounded by a membrane and filled with hydrolytic enzymes that act in an acidic environment. The enzyme composition of lysosomes is very diverse, it is formed by proteases (enzymes that break down proteins), amylases (enzymes for carbohydrates), lipases (lipid enzymes), nucleases (for the breakdown of nucleic acids), etc. In total, there are up to 40 different enzymes. When the membrane is damaged, enzymes enter the cytoplasm and cause rapid dissolution (lysis) of the cell. Lysosomes are formed by the interaction of CG and granular EPS. Lysosomal enzymes are synthesized in the granular ER and, using vesicles, are transported to the CG located next to the endoplasmic reticulum. Therefore, through the tubular expansion of the CG, enzymes move to its functional surface and are packaged into lysosomes.

Functions . Depending on their functions, different types of lysosomes are distinguished: phagolysosomes, autophagolysosomes, residual bodies, etc. Autophogolysosomes are formed by the fusion of a lysosome with an autophagosome, that is, vesicles containing the cell’s own macromolecular complexes, for example, entire cellular organelles, or their fragments that have lost their functional ability and are subject to destruction. phagolysosomes (phagosomes) are formed by combining lysosomes with phagocytic or pinocytotic vesicles, which contain material captured by the cell for intracellular digestion. The active enzymes in them are in direct contact with biopolymers that are subject to breakdown. Residual bodies- these are undivided particles surrounded by a membrane; they can remain in the cytoplasm for a long time and be utilized here or removed outside the cell by exocytosis. The residual bodies accumulate material, the breakdown of which is difficult (for example, a brown pigment - lipofuscin, which is also called the “aging pigment”). So, the main functions of lysosomes are:

1) autophagy - cleavage of the cell's own components, whole cells or their groups into autophagolysosomes (for example, resorption of the tail of a tadpole, the pectoral gland in adolescents, lysis of liver cells during poisoning)

2) heterophasia- breakdown of foreign substances in phagolysosomes (for example, breakdown of organic particles, viruses, bacteria that have entered the cell in one way or another)

3) digestive function - in unicellular organisms, endosomes fuse with phagocytic vesicles and form a digestive vacuole, which carries out intracellular digestion

4) excretory function- removal of undigested residues from the cell using residual bodies.

BIOLOGY +Storage diseases- hereditary diseases associated with the loss of certain enzymes by lysosomes. The consequence of this loss is the accumulation of undigested substances in the cells, interfering with the normal functioning of the cell. These diseases can be manifested by the development of the skeleton, individual internal organs, the central nervous system, etc. The development of atherosclerosis, obesity, etc. is associated with a deficiency of lysosome enzymes.

In the work proposed to you, we propose to consider the functions of lysosomes and their purpose. Among some purposes, we will highlight the more significant ones and write about them in more detail.

Let's start with the fact that everything is made of cells. These structural units are so small that we can only see them in the laboratory using special equipment. Now we are talking about a microscope; for the first time they are introduced to its structure in high school. Teachers offer several laboratory works using this tool to study the structure of onion scales or tree leaves.

A lysosome is a component of cells. We will talk about it further. Before considering the functions of lysosomes, we will briefly talk about the structure and significance of this organelle.

Lysosomes

We already indicated in the preface that these are the components of the cell, and translated from Latin they have a fairly clear meaning - the dissolution of the body. Lysosomes, the functions of which we will consider a little later, look like small organelles, they are surrounded by a membrane. The cavity of the lysosome is filled with hydrolytic enzymes, and an acidic environment is constantly maintained in it. What else is characteristic of the organelle we are considering? It does not have a constant form; they are always very diverse. Their sizes are very small, since one cell can contain several hundred lysosomes. Their diameter is approximately 0.2 microns.

Purpose

Before we look at the functions of lysosomes in a list, we will briefly outline the importance of this organelle in the cell. These points overlap greatly. It is important to mention that this organelle is absent in plant cells, but is present in humans and fungi. They are formed in the Golgi complex. We have already said that their cavities contain a very large number of different enzymes, thanks to which digestion occurs in the cells. Since these organelles are absent in plants, some of their functions can be performed by vacuoles.

• proteins;
• fats;
• carbohydrates;
• nucleic acids.

Another task of lysosomes is the breakdown of both individual parts and the entire cell. A good example here is the transformation of a tadpole into a frog. The tail disappears precisely under the influence of the enzymes of this organelle.

Functions

In this section, we propose to list the functions of lysosomes. The following can be distinguished:

• implementation of digestion in cells;
• autophagy;
• autolysis;
• dissolution.

To make it clearer, let us explain the meaning of the words “autophagy” and “autolysis”. In the first case, the destruction of unnecessary cell structures is implied, and in the second, self-digestion of the cell (we already mentioned this earlier in the example with the tadpole and the frog). In the last point we meant the dissolution of external structures.

Cell digestion

When we looked at it, we mentioned the ability of this organelle to carry out the digestion process in the cell. Before we begin to explain this function, it is necessary to clarify that there are several types of lysosomes. Namely:

• primary;
• secondary.

Primary lysosomes are also commonly called accumulative or storage granules. In this matter, we are more interested in secondary organelles. Since this includes:

• digestive vacuole;
• autophagy vacuole;
• residual body.

In the digestive vacuole, incoming substances are digested through hydrolysis. Digestion occurs, as a rule, to low molecular weight substances that can pass through the lysosome membrane. These substances are needed for important purposes - the synthesis of other organelles or intracellular structures.

Autophagy

The functions of the lysosome in the cell under consideration include an item called “autophagy”. Let's take a quick look at what this means. We have already said that this term refers to the destruction of unnecessary parts of the cell. This function is performed by secondary lysosomes, which are called autophagy vacuoles. They have a definite and constant oval shape, the body is quite large. It contains:

• fragments of mitochondria;
• cytoplasmic reticulum;
• ribosomes and so on.

That is, it contains the remains of the cell. They are susceptible to destruction under the influence of enzymes. The resulting residues do not disappear without a trace, but participate in other important processes.

These vacuoles can be found in very large numbers in a number of cases, including:

• starvation;
• intoxication;
• hypoxia;
• aging and so on.

Autolysis

So, we figured out what functions lysosomes perform. Now we propose to consider in more detail another of them, namely autolysis. The membranes of lysosomes can collapse, then the enzymes are released and cease to carry out their normal activities, since the cytoplasm has a neutral environment, and the enzymes in it are simply inactivated.

There are cases when all lysosomes are destroyed in such a way that leads to the death of the entire cell. Two groups of autolysis can be distinguished:

• pathological (the most striking and common example is the destruction of tissue after death);
• ordinary.