Mitochondria (from the Greek. Mitos-thread, chondrion-seed) - the organelles of eukaryotic cells, have their own DNA and performing the function of ATP synthesis. Size and shape of mitochondria varies greatly in different species. Usually the width of ~ 0.5 mm, length 7-60 mm. Mitochondria are moving, plastic, constantly changing shape, may ramify, to merge with each other, and diverge. Moving mitochondria associated with microtubules. But do plant cells have mitochondria? In the culture of endothelial cells of the heart tadpole xenops seen up to 40 cases of fusion and fission of mitochondria for 1 hour.
Mitochondria are located near sites of high ATP consumption (between myofibrils in cardiac muscle, around the sperm flagellum).
The number of mitochondria depends on the needs of the cell's energy, the greater the need, the more mitochondria in the cell and the more they are developed.
The complex shape of mitochondria makes it difficult to microscopic examination. To cut a convoluted mitochondrion can be represented several sections (3-5), and only the spatial three-dimensional reconstruction, based on a study of serial sections, may decide the question whether we are dealing with 3-6 individual mitochondria, or with a curved or branched.
In some cells, there is a much branched mitochondrion (unicellular green alga Polytomella, Engiena, Chlorella). Long branching mitochondria were described in mammalian tissue culture cells, cells of many plants in both normal and under anaerobic conditions.
In recent years become widely used for studying the properties of mitochondria fluorohrom Rhoda mine. This dye has the ability to laminate in purple light, when it binds to the membrane of active mitochondria. In the fluorescent microscope visible mitochondrial single system - the mitochondrial reticulum.
Liver cells have about 200 mitochondria. This is more than 20% of the total cytoplasm, and about 30-35% of total amount of protein in the cell. Surface area of all mitochondria of liver cells is 4-5 times greater than the surface of the plasma membrane. Most mitochondria in the oocytes (about 300000) and the giant amoeba Chaos (to 500000).
In the cells of green plants, the number of mitochondria is less than in animal cells as part of their functions could be the chloroplasts. In sperm are often present giant mitochondria helically coiled around the axis of the flagellum.
There are no mitochondria in intestinal entomb living in anaerobiosis, and some other parasitic protozoa.
Usually, mitochondria accumulate near those parts of the cytoplasm, where the need arises in the ATP formed in mitochondria. Thus, in skeletal muscle mitochondria are located near the myofibrils. In the sperm mitochondria form a spiral sheath around the axis of the flagellum, probably due to the need of ATP for movement of the sperm tail. Similarly in protozoa and in other cells, ciliated, mitochondria are located directly beneath the cell membrane at the base of cilia, for work which requires ATP. In the axons of nerve cells mitochondria are located around synapses, where the process of nerve impulse transmission.