Mitochondria definition: Mitochondria are sac like cell organelles present in the cytoplasm of a cell and they are engaged in energy production.
They do so by breakdown of carbohydrates in the presence of oxygen.
In short they are termed as power houses of the cell.
Also they are called as energy currencies of the cell.
They are the power generators of all big and small living beings .
Unlike other cell organelles they are extensively studied.
Characteristics of mitochondria:
Mitochondria are organs of special importance. These organelles are absolute requirements to sustain the physiological activities of the cells.
1. They are sac like or pouch like structures.
2. They are double membrane in nature.
The outer membrane is oval shaped without folding.
While the inner membrane is folded to form partitions termed cristae.
In the gap of these folding lies the matrix which encompasses all the enzymes and other substances which can help in production of energy as ATP.
For more on mitochondria anatomy refer the page.
3. They are present in almost all the cells of the body except in Red Blood Cells.
4. They are freely floating in the cytoplasm and and stay in the regions of high energy requirement.
5. Mitochondria are self replicable i.e. they can multiply on their own without the requirement of cell to divide. This characteristic feature helps replacement of old, worn out and damaged mitochondria with new and healthy mitochondria. This process happens many times in life cycle of a cell.
6. Mitochondria have their own genetic material as single stranded DNA. This DNA is unlike the double stranded one as in the cell nucleus.
7. They have capacity to generate mRNA which helps in formation of proteinacious enzymes required for the respiratory chain.
8. The mitochondria have many enzyme complex which in series help in formation of energy i.e. adenosine tri-phosphate (ATP).
9. In times of stress or injury, mitochondria can also play role in cell death. This cell death meditated by mitochondrial damage is in the form of apoptotic cell death. The mitochondrial damage leads to release of cell death factor (caspases).
10. If the mitochondria are killed, the whole cell dies immediately. That is the reason, how when cyanide is consumed, the person dies immediately. Cyanide immediately arrests the energy forming complexes leading to energy failure and death.
The mitochondria are transported or migrated through the long nerve cell. The Brain is high energy demanding organ and hence the number of mitochondria are more in a nerve cells. Nerve cells have a central nerve body and an extended lengthy axon with a nerve tip at the end. The mitochondria are formed in nerve body and then migrate towards the nerve tip. Nerve tip is involved in signal transmission, nerve growth and branching (plasticity). Hence healthy mitochondria are concentrated at the tip of nerve endings to cope up with the high energy demand and those mitochondria which are worn out, aged and damaged are migrated back from nerve tip to nerve body for digestion.