Mitochondria are one of the most important components of any cell. They are also called chondriosomes. These are granular or filiform organelles, which are an integral part of the cytoplasm of plants and animals. They are the producers of ATP molecules, which are so necessary for many processes in the cell.
What are mitochondria?
Mitochondria are the energy base of cells, their activity is based on the oxidation of organic compounds and the use of energy released during the decay of ATP molecules. In simple language, biologists call it a station for generating energy for cells.
In 1850, mitochondria were identified as granules in the muscles. Their number changed depending on growth conditions: they accumulate more in those cells where there is a large oxygen deficiency. This occurs most often during physical exertion. In such tissues, an acute shortage of energy appears, which mitochondria make up for.
The emergence of the term and place in the theory of symbiogenesis
In 1897, Bend first introduced the concept of “mitochondria” to indicate a granular and filamentous structure in the cytoplasm of cells. In shape and size, they are diverse: the thickness is 0.6 μm, the length is from 1 to 11 μm. In rare situations, mitochondria can be large and branched.
The theory of symbiogenesis gives a clear idea of what mitochondria are and how they appeared in cells. It says that the chondriosome arose in the process of destruction by bacteria cells, prokaryotes. Since they could not independently use oxygen for energy production, this prevented their full development, and progenoty could develop unhindered. Over the course of evolution, the link between them has enabled progenots to transfer their genes to eukaryotes now. Thanks to this progress, mitochondria are no longer independent organisms. Their gene pool cannot be fully realized, since it is partially blocked by enzymes that are in any cell.
Where do they live?
Mitochondria are concentrated in those areas of the cytoplasm where there is a need for ATP. For example, in the muscle tissue of the heart, they are located near myofibrils, and in spermatozoa form a protective mask around the axis of the tourniquet. There they generate a lot of energy so that the tail spins. This is how the sperm moves to the egg.
In cells, new mitochondria are formed by simple division of previous organelles. During it, all hereditary information is stored.
Mitochondria: how they look
The shape of mitochondria resembles a cylinder. They are often found in eukaryotes, occupying from 10 to 21% of the cell volume. Their sizes and shapes vary greatly and are able to vary depending on conditions, but the width is constant: 0.5-1 microns. The movements of chondriosomes depend on where in the cell a rapid waste of energy occurs. Move along the cytoplasm, using the cytoskeleton structure to move.
Long and branched mitochondria are a substitute for mitochondria of different sizes, working separately from each other and supplying energy to some areas of the cytoplasm. They are able to provide energy to sections of cells that are far from each other. Similar joint work of chondriosomes is observed not only in unicellular organisms, but also in multicellular ones. The most complex structure of chondriosomes is found in the muscles of the skeleton of mammals, where the largest branched chondriosomes are joined together using intermitochondrial contacts (MMC).
They are narrow gaps between adjacent mitochondrial membranes. This space has a high electron density. MMCs are more common in the cells of the heart muscle, where they bind together with working chondriosomes.
To better understand the issue, you need to briefly describe the importance of mitochondria, the structure and functions of these amazing organelles.
How are they arranged?
To understand what mitochondria are, it is necessary to know their structure. This unusual source of energy has the shape of a ball, but more often elongated. Two membranes are located close to each other:
- external (smooth);
- internal, which forms outgrowths of a leaf-shaped (crista) and tubular (tubule) form.
If you do not take into account the size and shape of the mitochondria, their structure and functions are the same. The chondriosome is delimited by two membranes, 6 nm in size. The outer mitochondrial membrane resembles a container that protects them from hyaloplasm. The inner membrane is separated from the outer by a section 11-19 nm wide. A distinctive feature of the inner membrane is its ability to protrude inside the mitochondria, taking the form of flattened ridges.
The internal cavity of the mitochondria is filled with a matrix, which has a fine-grained structure, where filaments and granules (15-20 nm) are sometimes found. Matrix strands create organelle
DNA molecules , and small-sized granules create mitochondrial ribosomes.
The synthesis of ATP in the first stage takes place in the hyaloplasm. At this stage, the initial oxidation of substrates or glucose to pyruvic acid occurs . These procedures are oxygen-free - anaerobic oxidation. The next stage of energy generation is aerobic oxidation and ATP decay; this process occurs in the mitochondria of cells.
What do mitochondria do?
The main functions of this organelle are:
The presence in the mitochondria of its deoxyribonucleic acid once again confirms the symbiotic theory of the appearance of these organelles. Also, in addition to the main work, they are involved in the synthesis of hormones and amino acids.
Mitochondrial Pathology
Mutations occurring in the mitochondrial genome lead to disastrous consequences. The carrier of human hereditary information is DNA, which is transmitted to descendants from parents, and the mitochondrial genome is transmitted only from the mother. This fact is explained very simply: children receive the cytoplasm with the chondriosomes enclosed in it together with the female egg, and they are absent in the spermatozoa. Women with this deviation can transmit mitochondrial disease to offspring, a sick man - no.
Under normal conditions, chondriosomes have the same copy of DNA - homoplasmy. Mutations can occur in the mitochondrial genome; heteroplasmy occurs due to the coexistence of healthy and mutated cells.
Thanks to modern medicine, more than 200 diseases have been identified to date, the cause of which was a mitochondrial DNA mutation. Not in all cases, but the therapeutic maintenance and treatment of mitochondrial diseases lend themselves well.
So we figured out the question of what mitochondria are. Like all other organelles, they are very important for the cell. They indirectly participate in all processes for which energy is needed.