What is mitochondria? Their structure and functions

Mitochondria are one of the most important constituents of any cell. They are also called chondriosomes. These are granular or filamentous organelles, which are 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 is mitochondria?

Mitochondria are the energy base of cells, their activity is based on the oxidation of organic compounds and the application of energy liberated during the decomposition of ATP molecules. Biologists in a simple language call it an energy production station for cells. In 1850 mitochondria were detected in the form of granules in muscles. Their number varied depending on the growth conditions: they accumulate more in those cells where there is a large deficit of oxygen. This happens most often with physical activity. In such tissues there is an acute shortage of energy, which is replenished by mitochondria.

The appearance of the term and place in the theory of symbiogenesis

In 1897, Bend first introduced the concept of "mitochondria" to denote a granular and filamentous structure in the cytoplasm of cells. In form and magnitude, they are diverse: the thickness is 0.6 μm, the length is from 1 to 11 μm. In rare situations mitochondria can be of large size and a branched junction.

In the theory of symbiogenesis, a clear idea is given of what mitochondria are and how they appeared in cells. It says that chondriosoma originated in the process of destruction of bacteria by bacteria, prokaryotes. Since they could not autonomously use oxygen to generate energy, this prevented their full development, and the progenitors could develop unhindered. Throughout evolution, the connection between them has enabled progenitors to transfer their genes now to eukaryotes. Thanks to this progress, mitochondria are no longer independent organisms. Their gene pool can not be fully realized, since it is partially blocked by enzymes that exist 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 the myofibrils, and in spermatozoa form a protective masking around the axis of the bundle. There they produce a lot of energy in order for the "tail" to spin. This is how the sperm moves to the egg.

In cells, new mitochondria are formed by the simple division of previous organelles. During it, all hereditary information is stored.

Mitochondria: how they look

The shape of the mitochondria resembles a cylinder. They are often found in eukaryotes, occupying 10 to 21% of the cell volume. Their sizes and shapes differ in many respects and are able to vary depending on the conditions, but the width is constant: 0.5-1 μm. The movements of the chondriosomes depend on where the cells spend a quick waste of energy. Moved along the cytoplasm, using to move the structure of the cytoskeleton. The replacement of mitochondria, which are different in size, working separately from one another and supplying some areas of the cytoplasm, are long and branched mitochondria. They are able to provide energy to cells that are far apart. Similar joint work of chondriosomes is observed not only in unicellular organisms, but also in multicellular organisms. The most complex structure of chondriomas is found in the muscles of the mammalian skeleton, where the largest branched chondriosomes adhere to each other using intermithochondrial contacts (MMC).

They are narrow gaps between adjacent mitochondrial membranes. This space has a high electron density. MMKs are more common in the cells of the heart muscle, where they bind together with working chondriosomes.

To better understand the issue, we need to briefly describe the significance of the mitochondria, the structure and functions of these amazing organelles.

How are they arranged?

To understand what mitochondria are, you need to know their structure. This unusual source of energy has the shape of a ball, but is more often drawn out. Two membranes are located close to each other:

• External (smooth);
• Internal, which forms the outgrowth of leafy (cristae) and tubular (tubula) forms.

If you do not take into account the size and shape of the mitochondria, their structure and functions are the same. The chondriosoma is delimited by two membranes, 6 nm in size. The outer membrane of the mitochondria resembles a container that protects them from the hyaloplasm. The internal membrane from the outer separates a section 11-19 nm in width. A distinguishing feature of the inner membrane is its ability to protrude into the mitochondria, taking the form of flattened crests.
The internal cavity of the mitochondria is filled with a matrix that has a fine-grained structure, where sometimes filaments and granules (15-20 nm) are detected. Matrix fibers create DNA molecules of organelles, and granules of small sizes are the mitochondria ribosomes.

Synthesis of ATP in the first stage occurs in the hyaloplasm. At this stage, there is an initial oxidation of substrates or glucose to pyruvic acid. These procedures go without oxygen - anaerobic oxidation. The next stage of energy formation is aerobic oxidation and decomposition of ATP, this process occurs in the mitochondria of cells.

What do mitochondria do?

The main functions of this organelle are:

• Energy production for cells;

• Storage of hereditary information in the form of its own DNA.

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 genome of the mitochondria lead to depressing consequences. The carrier of human genetic 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: the cytoplasm with the chondriosomes enclosed in it is given to the children along with the female ovum, they are absent in spermatozoa. Women with this abnormality can transmit mitochondrial disease to the offspring, the sick man is not.

Under normal conditions, chondriosomes have the same copy of DNA - homoplasmy. In the mitochondrial genome mutations can occur, due to the coexistence of healthy and mutated cells, heteroplasm appears.

Thanks to modern medicine to date, more than 200 diseases have been identified, the cause of which was the mutation of mitochondria DNA. Not all cases, but the therapeutic maintenance and treatment mitochondrial diseases succumb well.

So we figured out what the mitochondria are. Like all other organelles, they are very important for the cell. They indirectly participate in all processes for which energy is needed.