Mitochondria is majorly known as site of metabolism. It was discovered by collier in the flight muscles of insect. Term Fila was given by Fleming and term bio plast was given by Altmen .The term mitochondria was given by Benda.

 It is also called semi-autonomous organelle due its ability to perform certain activities. It is an important organelle in eukaryotes that produce adenosine triphosphate (ATP) which is the energy molecule for the cell. It is also called as the power house of cell. It is believed that mitochondria arises from free-living bacteria which were incorporated into cells.

Generally one mitochondria/cell is observed in unicellular organisms whereas 5 lakhs can be found in the flight muscle cells of insect which is the maximum observed till the date.

Structure of Mitochondria

  • Most common shape of mitochondria is disc or oval shape.
  • It have two membranes, an inner and outer membrane, which are made up of phospholipid layers.
  • Outer membrane has less proteins and they are permeable
  • Inner membrane is made up of several folds cristae, which increases the surface area. It also holds many proteins which supports the electron transport chain. It is semi-permeable. Many chemical reactions also take place in inner membrane. The increased surface area enhances the chemical reactions.
  • The inner area of mitochondria which is covered by inner membrane is called matrix. It is reach in enzymes foe cellular respiration and divalent ions like magnesium, ferric ions which are activators of enzyme present in matrix. It contains about 2/3 of total proteins. It is where the ATP production takes place. Space between inner and outer membrane is called perimitochondrial space.
  • Mitochondria have their own generic material and they produce their own RNA and protein. It also contains ribosomes.DNA present in mitochondria is reach in C and G nucleotides which results in the increase of denaturation temperature.
  • Mitochondria contains70s ribosomes .Generally 70s ribosomes are present in prokaryotes and this is the reason why Altman proposed a theory that eukaryotic mitochondria are either prokaryotic in origin or symbiotic.
  • But ribosomes in mammalian cells are 55s type. It has a larger subunit of 38s and smaller subunit of 28s.
  • It contains some nob like structures on cristae and this particles are called oxisomes.


  • Most important function of mitochondria is to produce ATP.The simpler molecules are sent to mitochondria to be converted to ATP molecules. This process is called oxidative phosphorylation.
  • It performs major functions like like oxidation, dehydration, oxidative phosphorylation.
  • It also produces heat and ions of calcium or phosphate.
  • It also helps to maintain proper concentration of calcium ions within the cell compartments.
  •  Helps in building certain parts of blood and hormones
  • Mitochondria play an important role in apoptosis.


Every year 1000 to 4000 children are born with mitochondrial disease in US. It is really difficult diagnosed.

In many cases, it is an inherited disease, it can also be due to environmental factors. Mutation in any one of the genes present in mitochondria can lead to mitochondrial disease. The mutation becomes so dangerous that it causes the proteins not to function properly.

This causes the mitochondria not to work properly which results in the decrease in the production of energy. Decrease in energy production can lead to any organ failure or even multiple organ failure.

There is no specific treatment for mitochondrial disease .It’s not having particular symptom or screening method which is the cause for misdiagnosis.

Symptoms can also include poor growth, developmental delays and muscle weakness. Mitochondrial diseases are generally transmitted by mother. Transmission of mitochondrial DNA mutation from mother can be reduced by mitochondrial replacement technique.

It is the replacement of mitochondria one or more cells. This technique uses healthy mitochondria of the donor’s egg. It is an in vito-fertilisatyion on which the mutated mitochondrial genes from mother’s cells is replaced by a third party.

The most common method in mitochondrial donation are maternal spindle fiber transfer using unfertilized egg and pronuclear transfer using fertilized egg. In maternal spindle fiber healthy nucleus of the mother is removed and from the donor egg is taken out without nucleus.

The healthy nucleus of the mother is now transferred to the donor egg and is fertilized. Pronuclear transfer involves the transfer of pronuclei from one zygote to another. It requires the fertilizes egg of donor also.

The healthy nucleus from the fertilized egg of parental couple is taken and the nucleus from donor egg is removed. Now the healthy nucleus is fused with the egg of donor. Mitochondrial disease include

  • Leigh Syndrome: It is a severe neuro disorder which is usually seen children. This leads to the eventual loss of mental and movement abilities. It results in patient’s death within 2-3 years due to respiratory failure. It can be due to the mutation or due to the deficiencies of pyruvate dehydrogenase enzyme. The symptoms also include weakness, muscle spasms. Lack of muscle ton, tremors which are symptoms of various other diseases also .Hence, it is really difficult to diagnose the disease.


Metabolism: an overview and types


  • About
  • Catabolism
  • Anabolism
  • Metabolic pathways


  • Metabolism is the collection of chemical reactions takes place to sustain life of an organism.
  • The main purposes of metabolism is to convert food to energy to run cellular activity; to convert food to building blocks for nucleic acids, lipids, protein and carbohydrates; and to remove metabolic waste.
  • The metabolic reactions which are enzyme catalysed are responsible for the growth and reproduction of organism, to maintain their structure and interact with environment.
  • Metabolic reaction is of two types one is catabolic reaction, means the breaking down of compounds and another is anabolic reaction- the building up of the compounds. The catabolic reaction liberates energy and the anabolic reaction uses energy.
  • Metabolic pathways include the steps through which one chemical is transformed into another and each step is facilitating by an enzyme.
  • Enzymes are the key component of the metabolic reaction; they act as catalyst- allows the reaction to proceed more rapidly.


Metabolic reaction is of two types:

  1. Catabolism
  2. Anabolism


  • In catabolism the compound through the set of chemical reaction is broken down into simpler compound or molecules.
  • This is achieved by breaking down and oxidizing food molecules.
  • Catabolism is responsible to provide energy for working of the cell and component needed for the anabolic processes which build molecules.
  • The nature of these catabolic reactions based on the source of energy and carbon which is differ from organism to organism.

The chief metabolic processes in a cell are:

  • Glycolysis
  • Pentose-phosphate pathway
  • Entner-doudoroff pathway
  • Tricarboxylic acid cycle
  • Fermentation
  • Glyoxylate cycle
  • Lipid hydrolysis
  • Protein hydrolysis


  • Anabolism is the set of constructive reactions which used energy released by the catabolic pathway to synthesize complex molecules.
  • The complex molecule construct cellular structure step by step, make up from small and simple precursor.
  • The biomolecules are necessary for the growth and reproduction, some biomolecule serve as the central metabolic intermediates.
  • Some organisms can synthesis all the necessary organic compound like autotrophs. They can be grown on simple media. On the other hand, the organisms which cannot synthesize organic compounds from atmosphere are known as fastidious organisms.
  • Following anabolic process takes place in organism:
  • Synthesis of glucose, lipids, amino acid and protein, nucleic acids
  • Synthesis of other growth factors like vitamins, hormones etc.

Metabolic process:


  • In the glycolysis process glucose and other sugar are partially oxidized to the smaller molecule i.e. pyruvate
  • Embden-Myerhof pathway, pentose phosphate pathway and Entner-Doudroff pathway are the three routes for the conversion of sugar into pyruvate.
  • It is anaerobic process in which organism obtain energy in the absence of oxygen, also called anerobic fermentation.

Tricarboxylic acid pathway:

  • Given by H. A. kerbs in 1973
  • Also known as citric acid cycle. Because citric acid is the first product of the kerb cycle which is as known as TCA cycle as the citric acid has three carboxylic group.

Glyoxyalte cycle:

  • It is anaplerotic reaction which means one product of a cycle is taken up by the other cycle
  • Oxaloacetate is taken from TCA cycle and used for carbon source from the amino acid synthesis.

Pentose phosphate pathway:

  • It is an alternative pathway for the sugar degradation.
  • Its main function is to generate power in the form of NADH in extramitochondrial cytoplasm and the second function is to convert hexoses into pentose for the synthesis of the nucleic acids. The third function is complete degradation of pentose.