The Structure and Function of Mitochondria

Edited by Chameleon, SarMal, Jen Moreau

Just like you rely on a healthy consumption of caffeine to get moving in the morning, the little cells that make up your body rely on Mitochondria to produce energy. Richard Altman first identified Mitochondria in 1890, labelling the little free floating organelles 'bioblasts.' This rather insipid term for such a potent part of the cell, was more appropriately coined 'mitochondria' in 1898 by Carl Benda derived from the Greek mito (thread) and kondros (granule), no doubt inspired by the structure of the interior of the mitochondria. Mitochondria was made famous by Philip Skiekevitz when he fittingly termed it the 'powerhouse of the cell' in 1957.

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The Structure and Function of Mitochondria

The mitochondria (plural mitochondria) is a membrane bound structure found in both eukaryotic plant and animal cells. The primary function of mitochondria is to provide the energy required for various cellular activities, most significantly the formulation of energy.

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Structure of Mitochondria

Mitochondria are rod-shaped, double membrane bound organelles. The outer and inner membranes of mitochondria are made up of proteins and phospholipids.

Mitochondria found in plant and animal cells comprise the following components:

Outer Membrane

The outer membrane of mitochondria surrounds the inner membrane, leaving a small space in between called the intermembrane space. The outer membrane has pores large enough to allow ions, molecules and small proteins to pass through.

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Inner Membrane

In contrast to the outer membrane, the inner membrane of mitochondria is much less porous, similar to the plasma membrane of a cell. The inner membrane folds over many times to create layered structures called cristae (singular crista). The folding of the inner membrane increases the surface area available for biochemical reactions. The shape and number of folds may vary. The inner membrane is full of proteins that aid in the movement of electrons as well as ATP synthesis.

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Mitochondrial Matrix

Mitochondrial matrix is the inner space enclosed by the inner membrane. The matrix contains a variety of enzymes and proteins that are important for energy production. Primarily, the mitochondrial matrix comprises of the following three types of molecules:

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  • Enzymes.The mitochondrial matrix contains hundreds of enzymes that take part in the Krebs cycle, also known as the tricarboxylic acid cycle (TCA). The TCA is a series of biochemical reactions that result in the production of energy in the form of adenosine triphosphate (ATP).
  • Ribosomes. Mitochondria contain ribosomes of 70S type, which is commonly found in prokaryotic cells. These ribosomes can synthesize proteins.
  • Mitochondrial DNA. Mitochondria have a small amount of DNA (mtDNA).
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Production of mtDNA

Located In order to convert chemical energy DNA located inside mitochondria, small organelles within the eukaryotic cells work at converting energy from food into ATP (an energy that cells can utilize). Although most of the DNA is found in the nucleus, the DNA found in mitochondria (mtDNA) does encode for 37 genes in humans, is inherited from the mother and was a significant portion of the first human genome to be sequenced [1].

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Function of Mitochondria

Mitochondria play a significant role in the production of the energy currency of the cell, ATP.

The process of energy production begins in the cytoplasm where glucose is metabolized to produce two 3-carbon molecules called Pyruvate. The conversion of glucose into pyruvate is known as glycolysis. The two pyruvate molecules are then transported into the mitochondria where they are metabolized to form 30 molecules of ATP. The breakdown of glucose into pyruvate is an aerobic process, which means that it cannot be performed in the absence of oxygen. In addition to pyruvate, mitochondria can also metabolize fatty acids to produce energy molecules. Apart from energy production, mitochondria also serve the following purposes:

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Production of Heat

Mitochondria are also involved in thermogenesis or production of heat. This process occurs in the mitochondria of cells of brown adipose tissues only. These tissues contain a protein called thermogenin. Thermogenin plays a role in the transportation of protons into the mitochondrial matrix. Brown adipose tissue or brown fat is found in the human body in small quantities only. It is found in hibernating animals primarily, such as bears, gray squirrels, and bats.

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Apoptosis

Apoptosis is the process of programmed cell death. During apoptosis, a number of cell changes occur, such as shrinkage of the cell, fragmentation of the nuclear structure, condensation of chromatic, etc. Mitochondria play a dual role in apoptosis. They protect the healthy cells while appropriate and facilitate apoptosis when required. During the process of apoptosis, a special type of protein is produced called proapoptotic proteins. These proteins enter the mitochondrial membrane and form pores in it. As a result, the proteins present within the mitochondria enter the cytosol and initiate a series of biochemical processes that result in the apoptotic death of the cell.

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Storage of Calcium Ions

While bones are the primary storage site of Calcium, at the cellular level, Calcium ions are stored in mitochondria and endoplasmic reticulum. Mitochondria store calcium for a short time only in order to maintain cell homeostasis.

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  1. Anderson, S.; Bankier, A. T.; Barrell, B. G.; de Bruijn, M. H. L.; Coulson, A. R.; Drouin, J.; Eperon, I. C.; Nierlich, D. P.; Roe, B. A.; Sanger, F.; Schreier, P. H.; Smith, A. J. H.; Staden, R.; Young, I. G. (1981). "Sequence and organization of the human mitochondrial genome". Nature. 290 (5806): 457�"65. Bibcode:1981Natur.290..457A. doi:10.1038/290457a0. PMID 7219534.

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Categories : Cell Biology

Recent edits by: SarMal, Chameleon

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