The mitochondria are organelles complex present only in eukaryotic cells.
Its function is to produce most of the energy of the cells , through a process called cellular respiration.
The size, shape, quantity and distribution of mitochondria vary according to the type of cell. They still have their own genetic material.
Mitochondria are formed by two lipoprotein membranes, one external and one internal:
- External membrane : similar to that of other organelles, smooth and composed of lipids and proteins called deporins, which control the entry of molecules, allowing the passage of relatively large ones.
- Internal membrane : it is less permeable and has numerous folds, called mitochondrial ridges.
The mitochondrial ridges protrude into the inner part of the mitochondria, a central space called the mitochondrial matrix, which is filled with a viscous substance containing respiratory enzymes that participate in the energy production process.
In the matrix are found ribosomes , organelles that produce proteins necessary for mitochondria. They are different from those found in the cell cytoplasm and more similar to that of bacteria. Another characteristic common to bacteria and mitochondria is the presence of circular DNA molecules.
The cellular respiration is a process of oxidation of organic molecules , such as glucides and fatty acids, in particular glucose , which is the main source of energy used by heterotrophic organisms.
Glucose comes from food (produced by autotrophic organisms through photosynthesis) and converted into carbon dioxide and water, producing molecules of ATP (adenosine triphosphate), which are used in various cellular activities.
This mode of energy production is very efficient, since there is a balance of 38 ATP, for each molecule of glucose, at the end of the process.
Glucose degradation involves several molecules, enzymes and ions and occurs in 3 stages: Glycolysis , Krebs Cycle and Oxidative Phosphorylation . The last two phases are the ones that most produce energy and occur in the mitochondria, while glycolysis occurs in the cytoplasm .
The general chemical equation for the process is represented as follows:
C 6 H 12 O 6 + 6 O 2 ⇒ 6 CO 2 + 6 H 2 O + Energy
How did mitochondria come about?
Mitochondria have biochemical and molecular characteristics similar to bacteria, such as the presence of circular DNA and ribosomes. For this reason, scientists believe that its origin is related to ancestral prokaryotic beings.
According to the Endosymbiotic Theory or Endosymbiogenesis , ancient prokaryotic organisms would have successfully hosted inside the eukaryotic cells of primitive organisms, evolving into the current mitochondria.
The same would have happened with chloroplasts , which resemble mitochondria due to the presence of a double membrane and its self-duplicating capacity.
- The word mitochondria derives from the Greek, myths (line / thread) + chondros (granule / grain).
- Mitochondria are spherical or elongated and have dimensions of approximately 0.5 to 1 µm in diameter. They can represent up to 20% of the total cell volume.
- The DNA of the mitochondria is exclusively maternal in origin.
- Mitochondria are also related to the process of cell death by apoptosis.