What is Mitochondria?
Popularly known as the “Powerhouse of the cell,” mitochondria (singular: mitochondrion) are a double-membrane-bound organelle found in most of the eukaryotic organisms. They are found inside the cytoplasm and essentially functions as the cell’s digestive system.
They play a major role in breaking down the nutrients and generating energy-rich molecules for the cell. Many of the biochemical reactions involved in cellular respiration take place within the mitochondria. The term ‘mitochondrion’ is derived from the Greek words “mitos” and “chondrion” which means “thread” and “granules-like” respectively. It was first described by a German pathologist named Richard Altmann in the year 1890.
Also refer: Cell Organelles
The diagram of mitochondria below explains the structural features of mitochondria.
Structure of Mitochondria
The mitochondrion is a double-membraned, rod-shaped structure found in both plant and animal cell. Its size ranges from 0.5 to 1.0 micrometre in diameter. The structure comprises an outer membrane, an inner membrane, and a gel-like material called the matrix. The outer membrane and the inner membrane are made of proteins and phospholipid layers separated by the intermembrane space.
The outer membrane covers the surface of the mitochondrion and has a large number of special proteins known as porins. It is freely permeable to ions, nutrient molecules, energy molecules like the ADP and ATP molecules.
The inner membrane of mitochondria is rather complex in structure. It has many folds that form a layered structure called cristae and this helps in increasing the surface area inside the organelle. The cristae and the proteins of the inner membrane aids in the production of ATP molecules. The inner membrane is strictly permeable only to oxygen and to ATP molecules. A number of chemical reactions take place within the inner membrane of mitochondria.
The mitochondrial matrix is a viscous fluid that contains a mixture of enzymes and proteins. It also comprises ribosomes, inorganic ions, mitochondrial DNA, nucleotide cofactors, and organic molecules. The enzymes present in the matrix play an important role in the synthesis of ATP molecules.
Function of Mitochondria
The most important function of mitochondria is to produce energy through the process of oxidative phosphorylation. It is also involved in the following process:
- Regulates the metabolic activity of the cell
- Promotes the growth of new cells and cell multiplication
- Helps in detoxifying ammonia in the liver cells
- Plays an important role in apoptosis or programmed cell death
- Responsible for building certain parts of the blood and various hormones like testosterone and oestrogen
- Helps in maintaining an adequate concentration of calcium ions within the compartments of the cell
- It is also involved in various cellular activities like cellular differentiation, cell signalling, cell senescence, controlling the cell cycle and also in cell growth.
Any irregularity in the way mitochondria functions can directly affect human health, but often, it is difficult to identify because symptoms differ from person to person. Disorders of the mitochondria can be quite severe, it can eventually cause an organ to fail.
Mitochondrial diseases: Alpers Disease, Barth Syndrome, Kearns-Sayre syndrome (KSS)
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