Covered with two membranes. The outer membrane is smooth, the inner one has inward growths - cristae, they increase the area of the inner membrane in order to place as many enzymes of cellular respiration on it as possible.
The internal environment of the mitochondria is called the matrix. It contains circular DNA and small (70S) ribosomes, due to which mitochondria independently make part of their proteins, which is why they are called semi-autonomous organelles. (The theory of symbiogenesis holds that previously mitochondria and plastids were free bacteria that were engulfed by a large cell but not digested.)
Function: mitochondria take part in cellular respiration (they are the “energy stations of the cell”).
Oxygen breathing (medium difficulty)
1. Glycolysis
Occurs in the cytoplasm. Glucose is oxidized to two molecules of pyruvic acid (PVA), releasing energy that is stored in 2 ATP and energy-rich electron carriers.
2. Oxidation of PVK in the mitochondrial matrix
PVC is completely oxidized to carbon dioxide, releasing energy that is stored in 2 ATP and energy-rich electrons on the carriers.
3. Respiratory chain
Occurs on the inner membrane of mitochondria. The energy-rich electrons obtained in the previous stages give up their energy, resulting in the formation of 34 ATP.
Mitochondria are microscopic membrane-bound organelles that provide the cell with energy. Therefore, they are called energy stations (battery) of cells.
Mitochondria are absent in the cells of simple organisms, bacteria, and entamoeba, which live without the use of oxygen. Some green algae, trypanosomes contain one large mitochondrion, and the cells of the heart muscle and brain have from 100 to 1000 of these organelles.
Structural features
Mitochondria are double-membrane organelles; they have outer and inner membranes, an intermembrane space between them, and a matrix.
Outer membrane. It is smooth, has no folds, and separates the internal contents from the cytoplasm. Its width is 7 nm and contains lipids and proteins. An important role is played by porin, a protein that forms channels in the outer membrane. They provide ion and molecular exchange.
Intermembrane space. The size of the intermembrane space is about 20 nm. The substance filling it is similar in composition to the cytoplasm, with the exception of large molecules that can penetrate here only through active transport.
Inner membrane. It is built mainly from protein, only a third is allocated to lipid substances. A large number of proteins are transport proteins, since the inner membrane lacks freely passable pores. It forms many outgrowths - cristae, which look like flattened ridges. The oxidation of organic compounds to CO 2 in mitochondria occurs on the membranes of the cristae. This process is oxygen-dependent and is carried out under the action of ATP synthetase. The released energy is stored in the form of ATP molecules and is used as needed.
Matrix– the internal environment of mitochondria has a granular, homogeneous structure. In an electron microscope, you can see granules and filaments in balls that lie freely between the cristae. The matrix contains a semi-autonomous protein synthesis system - DNA, all types of RNA, and ribosomes are located here. But still, most of the proteins are supplied from the nucleus, which is why mitochondria are called semi-autonomous organelles.
Cell location and division
Hondriom is a group of mitochondria that are concentrated in one cell. They are located differently in the cytoplasm, which depends on the specialization of the cells. Placement in the cytoplasm also depends on the surrounding organelles and inclusions. In plant cells they occupy the periphery, since the mitochondria are pushed towards the membrane by the central vacuole. In renal epithelial cells, the membrane forms protrusions, between which there are mitochondria.
In stem cells, where energy is used equally by all organelles, mitochondria are randomly distributed. In specialized cells, they are mainly concentrated in areas of greatest energy consumption. For example, in striated muscles they are located near the myofibrils. In spermatozoa, they spirally cover the axis of the flagellum, since a lot of energy is needed to set it in motion and move the sperm. Protozoa that move using cilia also contain large numbers of mitochondria at their base.
Division. Mitochondria are capable of independent reproduction, having their own genome. Organelles are divided by constrictions or septa. The formation of new mitochondria in different cells differs in frequency; for example, in liver tissue they are replaced every 10 days.
Functions in the cell
- The main function of mitochondria is the formation of ATP molecules.
- Deposition of calcium ions.
- Participation in water exchange.
- Synthesis of steroid hormone precursors.
Molecular biology is the science that studies the role of mitochondria in metabolism. They also convert pyruvate into acetyl-coenzyme A and beta-oxidation of fatty acids.
| Table: structure and functions of mitochondria (briefly) | ||
|---|---|---|
| Structural elements | Structure | Functions |
| Outer membrane | Smooth shell, made of lipids and proteins | Separates the internal contents from the cytoplasm |
| Intermembrane space | There are hydrogen ions, proteins, micromolecules | Creates a proton gradient |
| Inner membrane | Forms protrusions - cristae, contains protein transport systems | Transfer of macromolecules, maintenance of proton gradient |
| Matrix | Location of Krebs cycle enzymes, DNA, RNA, ribosomes | Aerobic oxidation with the release of energy, the conversion of pyruvate to acetyl coenzyme A. |
| Ribosomes | Combined two subunits | Protein synthesis |
Similarities between mitochondria and chloroplasts
The common properties of mitochondria and chloroplasts are primarily due to the presence of a double membrane.
Signs of similarity also include the ability to independently synthesize protein. These organelles have their own DNA, RNA, and ribosomes.
Both mitochondria and chloroplasts can divide by constriction.
They are also united by the ability to produce energy; mitochondria are more specialized in this function, but chloroplasts also produce ATP molecules during photosynthetic processes. Thus, plant cells have fewer mitochondria than animal cells, because chloroplasts partially perform the functions for them.
Let us briefly describe the similarities and differences:
- They are double-membrane organelles;
- the inner membrane forms protrusions: cristae are characteristic of mitochondria, and thillacoids are characteristic of chloroplasts;
- have their own genome;
- capable of synthesizing proteins and energy.
These organelles differ in their functions: mitochondria are intended for energy synthesis, cellular respiration occurs here, chloroplasts are needed by plant cells for photosynthesis.
What are mitochondria? If the answer to this question is difficult for you, then our article is just for you. We will consider the structural features of these organelles in relation to the functions they perform.
What are organelles
But first, let's remember what organelles are. This is what permanent cellular structures are called. Mitochondria, ribosomes, plastids, lysosomes... All these are organelles. Like the cell itself, each such structure has a general structural plan. Organelles consist of a surface apparatus and internal contents - the matrix. Each of them can be compared to the organs of living beings. Organelles also have their own characteristic features that determine their biological role.
Classification of Cell Structures
Organelles are divided into groups based on the structure of their surface apparatus. There are single-, double- and non-membrane permanent cellular structures. The first group includes lysosomes, the Golgi complex, the endoplasmic reticulum, peroxisomes and various types of vacuoles. The nucleus, mitochondria and plastids are double-membrane. And ribosomes, the cell center and organelles of movement are completely devoid of surface apparatus.
Symbiogenesis theory
What are mitochondria? For evolutionary teaching, these are not just cell structures. According to the symbiotic theory, mitochondria and chloroplasts are the result of metamorphoses of prokaryotes. It is possible that mitochondria originated from aerobic bacteria, and plastids from photosynthetic bacteria. Proof of this theory is the fact that these structures have their own genetic apparatus, represented by a circular DNA molecule, a double membrane and ribosomes. There is also an assumption that animal eukaryotic cells subsequently evolved from mitochondria, and plant cells from chloroplasts.
Location in cells
Mitochondria are an integral part of the cells of the majority of plants, animals and fungi. They are absent only in anaerobic unicellular eukaryotes living in an oxygen-free environment.
The structure and biological role of mitochondria have long remained a mystery. They were first seen using a microscope by Rudolf Kölliker in 1850. In the muscle cells, the scientist discovered numerous granules that looked like fluff in the light. Understanding the role of these amazing structures was made possible thanks to the invention of University of Pennsylvania professor Britton Chance. He designed a device that allowed him to see through organelles. This is how the structure was determined and the role of mitochondria in providing energy to cells and the body as a whole was proven.
Shape and size of mitochondria
General plan of the building
Let's consider what mitochondria are from the point of view of their structural features. These are double-membrane organelles. Moreover, the outer one is smooth, and the inner one has outgrowths. The mitochondrial matrix is represented by various enzymes, ribosomes, monomers of organic substances, ions and clusters of circular DNA molecules. This composition makes it possible for the most important chemical reactions to occur: the tricarboxylic acid cycle, urea, and oxidative phosphorylation.
The meaning of kinetoplast
Mitochondria membrane
Mitochondria membranes are not identical in structure. The closed outer one is smooth. It is formed by a bilayer of lipids with fragments of protein molecules. Its total thickness is 7 nm. This structure performs the functions of delimitation from the cytoplasm, as well as the relationship of the organelle with the environment. The latter is possible due to the presence of the porin protein, which forms the channels. Molecules move along them through active and passive transport.
The chemical basis of the inner membrane is proteins. It forms numerous folds inside the organoid - cristae. These structures significantly increase the active surface of the organelle. The main feature of the structure of the inner membrane is complete impermeability to protons. It does not form channels for the penetration of ions from the outside. In some places the outer and inner contact. A special receptor protein is located here. This is a kind of conductor. With its help, mitochondrial proteins, which are encoded in the nucleus, penetrate into the organelle. Between the membranes there is a space up to 20 nm thick. It contains various types of proteins, which are essential components of the respiratory chain.
Functions of mitochondria
The structure of the mitochondrion is directly related to the functions it performs. The main one is the synthesis of adenosine triphosphate (ATP). This is a macromolecule that is the main carrier of energy in the cell. It consists of the nitrogenous base adenine, the monosaccharide ribose and three phosphoric acid residues. It is between the last elements that the main amount of energy is contained. When one of them ruptures, a maximum of 60 kJ can be released. In total, a prokaryotic cell contains 1 billion ATP molecules. These structures are constantly in operation: the existence of each of them in an unchanged form does not last more than one minute. ATP molecules are constantly synthesized and broken down, providing the body with energy at the moment it is needed.
For this reason, mitochondria are called "energy stations." It is in them that the oxidation of organic substances occurs under the action of enzymes. The energy that is generated in this case is stored and stored in the form of ATP. For example, when 1 g of carbohydrates is oxidized, 36 macromolecules of this substance are formed.
The structure of mitochondria allows them to perform another function. Due to their semi-autonomy, they are an additional carrier of hereditary information. Scientists have found that the DNA of the organelles themselves cannot function independently. The fact is that they do not contain all the proteins necessary for their work, so they borrow them from the hereditary material of the nuclear apparatus.
So, in our article we looked at what mitochondria are. These are double-membrane cellular structures, in the matrix of which a number of complex chemical processes take place. The result of the work of mitochondria is the synthesis of ATP, a compound that provides the body with the necessary amount of energy.
Characteristic of the vast majority of cells. The main function is the oxidation of organic compounds and the production of ATP molecules from the released energy. The small mitochondrion is the main energy station of the entire body.
Origin of mitochondria
Today, there is a very popular opinion among scientists that mitochondria did not appear in the cell independently during evolution. Most likely, this happened due to the capture by a primitive cell, which at that time was not capable of independently using oxygen, of a bacterium that could do this and, accordingly, was an excellent source of energy. Such a symbiosis turned out to be successful and took hold in subsequent generations. This theory is supported by the presence of its own DNA in mitochondria.
How are mitochondria structured?
Mitochondria have two membranes: outer and inner. The main function of the outer membrane is to separate the organelle from the cell cytoplasm. It consists of a bilipid layer and proteins that penetrate it, through which the transport of molecules and ions necessary for work is carried out. While smooth, the inner one forms numerous folds - cristae, which significantly increase its area. The inner membrane is largely composed of proteins, including respiratory chain enzymes, transport proteins, and large ATP synthetase complexes. It is in this place that ATP synthesis occurs. Between the outer and inner membranes there is an intermembrane space with its inherent enzymes.
The inner space of mitochondria is called the matrix. Here are located the enzyme systems for the oxidation of fatty acids and pyruvate, enzymes of the Krebs cycle, as well as the hereditary material of mitochondria - DNA, RNA and the protein synthesizing apparatus.
What are mitochondria needed for?
The main function of mitochondria is the synthesis of a universal form of chemical energy - ATP. They also take part in the tricarboxylic acid cycle, converting pyruvate and fatty acids into acetyl-CoA and then oxidizing it. In this organelle, mitochondrial DNA is stored and inherited, encoding the reproduction of tRNA, rRNA and some proteins necessary for the normal functioning of mitochondria.
Genes that remained during evolution in the “energy stations of the cell” help to avoid management problems: if something breaks in the mitochondria, it can fix it itself, without waiting for permission from the “center.”
Our cells receive energy with the help of special organelles called mitochondria, which are often called the energy stations of the cell. Externally, they look like tanks with a double wall, and the inner wall is very uneven, with numerous strong indentations.
A cell with a nucleus (colored blue) and mitochondria (colored red). (Photo by NICHD/Flickr.com)
Mitochondria in section, outgrowths of the inner membrane are visible as longitudinal internal stripes. (Photo by Visuals Unlimited/Corbis.)
A huge number of biochemical reactions occur in mitochondria, during which “food” molecules are gradually oxidized and disintegrated, and the energy of their chemical bonds is stored in a form convenient for the cell. But, in addition, these “energy stations” have their own DNA with genes, which is served by their own molecular machines that provide RNA synthesis followed by protein synthesis.
It is believed that mitochondria in the very distant past were independent bacteria that were eaten by some other single-celled creatures (most likely archaea). But one day the “predators” suddenly stopped digesting the swallowed protomitochondria, keeping them inside themselves. A long rubbing of the symbionts with each other began; as a result, those who were swallowed greatly simplified their structure and became intracellular organelles, and their “hosts” were able, due to more efficient energy, to develop further into more and more complex forms of life, up to plants and animals.
The fact that mitochondria were once independent is evidenced by the remains of their genetic apparatus. Of course, if you live inside with everything ready-made, the need to contain your own genes disappears: the DNA of modern mitochondria in human cells contains only 37 genes - against 20-25 thousand of those contained in nuclear DNA. Over millions of years of evolution, many of the mitochondrial genes have moved to the cell nucleus: the proteins they encode are synthesized in the cytoplasm and then transported to the mitochondria. However, the question immediately arises: why did 37 genes still remain where they were?
Mitochondria, we repeat, are present in all eukaryotic organisms, that is, in animals, plants, fungi, and protozoa. Ian Johnston ( Iain Johnston) from the University of Birmingham and Ben Williams ( Ben P. Williams) from the Whitehead Institute analyzed more than 2,000 mitochondrial genomes taken from various eukaryotes. Using a special mathematical model, the researchers were able to understand which genes were more likely to remain in the mitochondria during evolution.