Some of the main functions of Mitochondria are as follows:
1. Centre of respiration:
Mitochondria are the respiratory centres, of cell. This view was postulated by Kingsbury (1912). They store energy in the form of adenosine triphosphate (ATP) which is released during glycolysis, Krebs cycle and electron transport mechanism of cell respiration.
Glycolysis occurs in the cytoplasm of the cell, Krebs cycle takes place in the mitochondria.
During this process the metabolic end products of various food stuffs, i.e., glucose or glycogen, amino acids and fatty acids, are degraded to CO2 and water with the use of O2, and energy is liberated.
This energy is locked in adenosine triphosphate (ATP), which is utilized in various body activities.
Glycolysis (Glucose to acetyl coenzyme A):
Glucose + 2ADP + 2 phosphate + 4 NAD + 2 Coenzyme A → 2 acetyl coenzyme A + 2СО2 + 2 ATP + 4 NADH + 4H + (ATP yield-2)
2 Acetyl coenzyme A + 6H2O + 2 ADP + 2 phosphate + 2 FAD + 4 NAD → 6CO2 + 4 ATP + 2 FADH2 + 10 NADH + 10 H+ (ATP yield-2)
2 FADH2 + 4 ADP + 4 phosphate + O2 → 2 FAD + 4 ATP + 2H2O and (ATP yield-4)
10NADH + 10 H+ +30 ADP + 30 phosphate + 5O2 → 10 NAD + 30 ATP + 10 H2O (ATP yield-30)
2. Proteolytic activity:
Horning described that mitochondria have proteolytic enzyme activity. In Protozoa, he has demonstrated both lytic and synthetic activity of mitochondria. In Amoeba, he found that pieces of engulfed food circulate in cytoplasm and later they become associated with mitochondria.
He is of opinion that mitochondria are responsible for the production of zymogen granules of pancreas.
Levi and Chevremont believe that myofibrils have mitochondrial organ. According to them, these mitochondria help in histogenesis (especially neurofibrils and muscle fibrils).
4. Fat metabolism:
Wotton suggested by studying mitochondria of trypanosomes that these are associated with metabolism of fat. Recently, evidence of fat metabolism comes from Bensley (1947) on mitochondria of liver cells. Finally, he suggested that mitochondria really represent a reserve store of metabolic material for cell. In germinating seeds these help in diastatic activity.
5. Hereditary function:
Recently, Luck et al., (1964) have discovered that mitochondria serve as cytoplasmic genes. They carry characters and thus help in genetic continuity of traits.
6. They play an important part in the formation of germ cells during its division (i.e., chondriokinesis).
7. Mitochondria are self-replicating organelles. Replication occurs in response to physiological requirements. They contain DNA, ribosomes and necessary enzymes to carry on protein synthesis as well as synthesis of phospholipids and other low molecular weight constituents.
8. Formation of mitochondrial spiral in the developing sperm:
During maturation of a spermatid into a spermatozoon, the mitochondria form a spiral sheath around the axial filament of the middle piece of spermatozoon. Sheath is actually an end-to-end association of elongated mitochondria. They provide energy for the movement of sperm.
9. In the oocytes of frog, Rana pipiens and fresh water snail, Planorbis, some of the mitochondria are transformed into yolk bodies. Yolk platelets accumulate inside the mitochondria and displace the cristae toward the periphery, transforming the mitochondria into yolk bodies.
10. Mitochondria is as a reservoir of energy:
It is a source of energy for cellular activities.
11. In the flight muscles of insects, the mitochondria (called sarcosomes here) are intimately associated with the endoplasmic reticulum. They presumably develop endoplasmic reticulum (e.g. rat liver cells).