June 12, 2021


5 min read




In this article, we shall discuss the definition of mitochondria.


The mitochondrion is known as the powerhouse of the cell. It is because it provides energy to the cell when a cell is in need of energy. It is a double membrane organelle. Basically, there are three types of organelle present in a cell, non- membranous, membranous, and double membranous. A  Mitochondrion is one of the double-membrane organelles.


A mitochondrion is a self-replicating organelle. In a Plant cell, there are three types of self-replicating organelles(a) chloroplast(b) mitochondria (c) nucleus. When a cell divides into two cells during mitosis its mitochondria also divide. Mitochondria have their own DNA. It can decrease or increase its number on the demand of the cell. Lysosomes have the ability to digest mitochondria by the process of autophagy.

For example, eye cells require less energy because eye cells do not do more work so numbers of mitochondria are less in these cells. On contrary, when we engage in a hard exercise our muscle cells need more energy so numbers of mitochondria start to increase. That’s why it is called self-replicating organelle. A mitochondrion is a self-autonomous organelle as well because it depends 50% on the nucleus and 50% remains independent.


Mitochondria vary from cell to cell in size. Its size is from 5-7 micro mete in different cells.


Mitochondria present in different shapes in cells. They are rod-like, filamentous and vesicle in shape.


As discussed earlier that mitochondria are present in different numbers in different cells. Those cells that need more energy have a large number of mitochondria and those cells that require less energy have less number of mitochondria.


As for as mitochondria concern, it is a double membrane organelle. Its outer membrane is smooth while its inner membrane forms infoldings. Each infolding is so-called crista (plural cristae). The space present between the outer membrane (OM) and inner membrane (IM) is called inner membrane space (IMS) or outer chamber (OC). The space present inside the inner membrane is known as a mitochondrial matrix or inner chamber(IC). The mitochondrial matrix is a fluid-filled space. In mitochondrial matrix DNA is present,  it is because they are self-replicating organelles. The mitochondrial matrix also contains its RNA and ribosomes, so they have the ability to prepare protein. Besides DNA, RNA, and ribosomes mitochondria also have enzymes as well as co-enzymes. Both enzymes and co-enzymes control metabolism in mitochondria.


 In cristae which are present in the inner membrane, there are few particles are attached which are called F1 particles. F1 particles like the knob of the door. These particles take part in the respiration process.


Mitochondria perform different functions in a cell. As described before they are the powerhouse of cells, as they provide energy to the cells when cells require energy. Energy production is related to the formation of ATP. ATPs are produced in both aerobic and anaerobic respiration. Aerobic respiration takes place in the presence of oxygen, while anaerobic respiration takes place in the absence of oxygen. Anaerobic respiration is totally absent in mitochondria. Only aerobic respiration carries out in them. Basically, the respiration process consists of 3 steps viz,(a) glycolysis (b) Kreb’s cycle, and(c)  electron transport chain. Glycolysis is common in both types of respiration. It occurs in the cytoplasm of the cell. But next two steps after glycolysis take place in mitochondria. Kreb’s cycle occurs in matrix and electron transport chain (ETC) is carried out in F1 particles.

In prokaryotic cell 1 glucose molecule produces 38 ATPs, while in eukaryotic cell 1 glucose molecule produces 36 ATPs. Mitochondria also carry out fatty acid metabolism. The production of ATP is called phosphorylation.


Different metabolic pathways take place inside mitochondria. (1) Kreb’s cycle (2) fatty acids metabolism (3) Urea cycle (4) Biosynthesis of Heme (5) Lipid Biosynthesis metabolism (6) Biosynthesis of F.S centers.


(1)Maternal  VS spondaic inheritance (2) mtDNA point mutation and maternal inheritance  (3) mapping mtDNA deletion/re-arrangements. (4) Molecular genetics of human mitochondrial diseases (5) mitochondrial mutations in micro-organisms (6) mitochondrial mutations in mammalian cells (7) mtDNA deletions-Kearns Sayre syndrome and Pearson syndrome. (8) Nuclear mutations and mitochondrial disease (9) Defective ETC (10) Mitochondria and Apoptosis (11) Mitochondrial DNA sequencing and Anthropology points


Richard Altmann in 1890 established them as cell organelle and called them bioblasts. Plant mitochondria were first described in 1904 by Meres. In 1857 Kolliker discovered them in muscle cells. In 1929 Karl Lohmann discovered ATP.


  • Production of ATP
  • Calcium Homeostasis
  • Regulation of innate immunity
  • Programmed cell
  • Stem cell regulation


Mitochondria have an important role in cellular respiration through ATP, using chemical energy found in glucose and other nutrients. Mitochondria are also responsible for generating clusters of iron and sulfur, which are important cofactors of many enzymes. They fulfill various vital roles in cellular metabolism. They are commonly known as the power of the house of the cell for their pivotal role. Mitochondria also play a crucial role in respiration, genetic illness, aging, and self-destruction of cells.

The energy generating capacity of mitochondria was described by Mithcell in 1961 and awarded the Noble Prize in 1978 in chemistry. Mithcell‘s chemiosmotic theory described how the nutritional substrate is coupled to the synthesis of ATP, the compound in which cellular energy is considered. In mitochondria the macronutrients derived reducing equivalent NADH and FADH2.


Mitochondrial respiration is transiently resumed early after HI followed by a secondary decline preceding the development of secondary brain injury 84. During this latent phase, ATP production is maintained through both oxidative metabolism and anaerobic cycling of glucose to lactate 7, but many mitochondria are swollen and overloaded with calcium 85, indicating that they are in a vulnerable state unless repair processes mitochondrial biogenesis are activated at this stage, high production of mitochondria are at risk of undergoing eliciting apoptosis or regulated cell death.

Impaired mitochondrial metabolism associated with respiratory chain dysfunction and oxidative stress is considered to be a major pathological mechanism in a number of neuro-generative diseases including AD.



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