Mitochondria are the cell organelles which produce energy.
They are small sac-like structures floating in the cell.
They are the places where tri-carboxylic acid cycle occurs leading to complete breakdown of glucose into water and carbon dioxide.
In doing so, they produce energy by oxidative phosphorylation.
A cell cannot survive without mitochondria. Hence mitochondria are present in both plant and animal cells.
Below are some interesting facts on mitochondria. But before you go through it, kindly refer to the information regarding the structure and function of mitochondria if you are not aware of in the video below.
Mitochondria Facts in cell
1. Mitochondrial fusion: Mitochondria fusion is a process where mitochondria merge to form tubular networks. This process can also be reversed as they can also go for fission. This fusion and fission is a dynamic process meant to maintain the health of the cell. This process is especially active in stressful conditions to overcome genetic malfunction. Fusion activity leads to elongated mitochondria while fission activity leads to fragmentation. This is an interesting concept on how cell survives stress through dynamics of mitochondria.
2. Single-stranded DNA & ribosomes: They have their own cDNA which is single stranded. They can multiply on their own without the involvement of the cell division.
Credit: few in numberNational Human Genome Research Institute Wikimedia Commons
Also, mitochondria have separate ribosomes which are also different in size than normal ribosomes present near the nucleus.
3. Semi-autonomous organelles: Mitochondria are semi-autonomous organelles due to the presence of DNA and own ribosomes. They can multiply on their own and also form required proteins without the involvement of nucleus.
4. Complex enzymes: The matrix of mitochondria have four complex enzymes which help in its function. These complex-enzymes include
Complex-I which is a combination of NADH-Q-Reductase. It contributes to translocate protons across membranes.
Complex-II is a combination of Succinate-Q-Reductase made of two polypeptides.
Complex-III is QH2-Cytochrome-C-reducatse.
Complex-IV is Cytochrome-C-Oxidase.
These complex-enzymes help in generation of ATP which acts as energy for the cell. This ATP production involves the coupling of oxidative phosphorylation.
5. Cell death: They are also essential cell organelles involved in cell death. They initiate programmed cell death by a process called as apoptosis. See the role of mitochondria in cell death.
6. Number of mitochondria per cell: Liver cells contains approximately 1600 mitochondria, while kidney cells have 1000 mitochondria, while some oocytes around 300000 mitochondria.
7. Structural changes: Though mitochondria of different cells are similar in an animal, they vary slightly in structure.
The cells of skin have mitochondria which have less folding in the inner membrane to form cristae.
While those of muscle cell have more folding to form more cristae. The more the cristae, the higher is the respiratory capacity and the energy generation.
Mitochondria in diseases:
8. Mitochondrial drugs and diseases: Defects in mitochondria can lead to few diseases. And hence drugs are being developed which target mitochondria for the treatment of diseases.
9. Death by poisons: Many poisons like cyanide cause death due to their action on mitochondrial enzymes. Poisons like heavy metals and cyanide inhibit the function of complexes within the mitochondria leading to the instant death of animals. Lethal injections used in death penalty contain cyanide also kill by arresting the energy production from mitochondria.
10. Isolation for experiments: Though they are very minute in size, they can be isolated for testing and diagnosis in labs. Their specific gravity is more than the cytoplasm. Hence they can be isolated from cells and tissue homogenates by ultra-centrifugation.
They can be observed under the microscope by staining with Janus green. Dark field illumination with phase contrast setting helps in viewing them.
Also, the number of mitochondria vary in between plants and animals. Plant cells have fewer mitochondria than animals cells.