external image 350px-Mitochondria%2C_mammalian_lung_-_TEM.jpg Electron micrograph of a mitochondrion from mammalian lung tissue showing its matrix and membranes.
In cell biology, a mitochondrion (plural mitochondria) is a membrane-enclosed organelle found in most eukaryotic cells.[1[[http://en.wikipedia.org/wiki/Mitochondrion#cite_note-mitosomes-0|]]] These organelles range from 1–10 micrometers (μm) in size. Mitochondria are sometimes described as "cellular power plants" because th;,';p[lk'poey generate most of the cell's supply of adenosine triphosphate (ATP), used as a source of chemical energy. In addition to supplying cellular energy, mitochondria are involved in a range of other processes, such as signaling, cellular differentiation, cell death, as well as the control of the cell cycle and cell growth.[2[[http://en.wikipedia.org/wiki/Mitochondrion#cite_note-1|]]] Mitochondria have been implicated in several human diseases, including mental disorders[3[[http://en.wikipedia.org/wiki/Mitochondrion#cite_note-2|]]] and cardiac dysfunction,[4[[http://en.wikipedia.org/wiki/Mitochondrion#cite_note-3|]]] and may play a role in the aging process. The word mitochondrion comes from the Greek μίτος or mitos, thread + χονδρίον or khondrion, granule. Their ancestry is not fully understood, but, according to the endosymbiotic theory, mitochondria are descended from ancient bacteria, which were engulfed by the ancestors of eukaryotic cells more than a billion years ago.
Several characteristics make mitochondria unique. The number of mitochondria in a cell varies widely by organism and tissue type. Many cells have only a single mitochondrion, whereas others can contain several thousand mitochondria.[5[[http://en.wikipedia.org/wiki/Mitochondrion#cite_note-Alberts-4|]]][6[[http://en.wikipedia.org/wiki/Mitochondrion#cite_note-Voet-5|]]] The organelle is composed of compartments that carry out specialized functions. These compartments or regions include the outer membrane, the intermembrane space, the inner membrane, and the cristae and matrix. Mitochondrial proteins vary depending on the tissues and species. In human, 615 distinct types of proteins were identified from cardiac mitochondria;[7[[http://en.wikipedia.org/wiki/Mitochondrion#cite_note-6|]]] whereas in murine, 940 proteins encoded by distinct genes were reported.[8[[http://en.wikipedia.org/wiki/Mitochondrion#cite_note-7|]]] The mitochondrial proteome is thought to be dynamically regulated.[9[[http://en.wikipedia.org/wiki/Mitochondrion#cite_note-8|]]] Although most of a cell's DNA is contained in the cell nucleus, the mitochondrion has its own independent genome. Further, its DNA shows substantial similarity to bacterial genomes.[10[[http://en.wikipedia.org/wiki/Mitochondrion#cite_note-9|]]]

**Mitochondria** - Mitochondria are oblong shaped organelles that are found in the cytoplasm of every eukaryotic cell. In the animal cell, they are the main power generators, converting oxygen and nutrients into energy.

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A cross-section of a mitochondrion (above) and a 3-D cutaway. Mitochondria have an outer membrane and an inner membrane. The inner membrane is much folded to form christae. Mitochondria have their own DNA and ribosomes. Mitochondria each have 37 genes.external image CeelMitochondria.gif

Nutrition and energy production: the mitochondria

The cell membrane encloses your cells like your skin encloses your body and, in the same way that your body has tissues and organs within it to support your overall function, each of your cells has its own miniaturized version of tissues and organs. The miniaturized organs are called organelles, and they carry out much of the day-to-day functions in your cell. Some of the most important organelles in your cells are the energy-producing powerhouses, called the mitochondria.
The mitochondria are the place where your cells produce the energy they need from the nutrients in the food you eat. Each of your cells has several hundred to over two thousand mitochondria inside of them, depending on their need for energy. For instance, heart cells and the cells in your skeletal muscle, which have very high energy demands to support the constant movements within your body, have up to 40% of their space taken up by mitochondria. All together, your body has over one quadrillion mitochondria that are constantly producing energy.

How Mitochondria produce energy
Mitochondria use oxygen and the nutrients from the food you eat to produce energy. Most of the energy produced by your mitochondria comes from breakdown of glucose or fat from your diet. Since the mitochondria produce the energy used by other parts of your cells and throughout your body, they must have some way to transport this energy. They do this using a molecule called adenosine triphosphate, or ATP. ATP is like an energy currency in your body: it can be produced in one part of the cell and transported to another place where it is "spent" for energy.
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ATP transports energy through a high-energy phosphate that is removed at the site where its energy is used. When ATP gives up, or "spends," its energy, such as when your muscles need energy for movement, this high-energy phosphate is stripped off the ATP, and it becomes adenosine diphosphate, or ADP. ADP is then transported back to your mitochondria, where it can have another high-energy phosphate put on it to form ATP again, and therefore -- like an energy shuttle moving the energy back and forth - it is used and reused to transport energy.

On an average day in which you are not doing anything particularly strenuous, you will use the equivalent of roughly half of what you weigh in ATP, about 40 kilograms. Approximately 90% of the oxygen you breathe will be used by your mitochondria to produce this energy. Since the ATP is recycled to ADP and then converted back to ATP to transport more energy, you don't gain or lose weight in this energy generation process. The production of energy uses a multitude of nutrients, as well as many other molecules from food. Let's take a closer look at the chemical reactions involved in energy production and where these nutrients function during the production of ATP.
What nutrients do mitochondria need?

The attachment of the high-energy phosphate to ADP to form ATP is a complex process -- not surprising, since energy is the basis for everything that happens in your body and is what drives life at its most basic level. Mitochondria are like cells within your cells; they have a membrane made of fats and proteins like your cell's membrane. In contrast to your cells' outer membrane, however, each mitochondrion has two membranes, an inner and an outer membrane. Its inner membrane is composed of up to 75% protein, much more than any other membrane in your cell. These proteins are part of the electron transport chain (ETC) and are the key players in generating ATP.

The food you eat must first be prepared for the ETC. To do that, your body takes the glucose or fat molecule and breaks it down to smaller units of two carbons. These two-carbon units are then stripped of some of the energy units, called electrons, and broken down to carbon dioxide, which is transported out of the mitochondria as a waste product. A small amount of energy is generated during this process, which is called the Kreb's cycle. The main role of the Kreb's cycle, however, is to strip electrons from the glucose and fats for energy production through the ETC, which will generate the most energy. The Kreb's cycle uses a multitude of vitamins and minerals, in particular the B-vitamins, vitamin B1, B2, B3, B5, and B6; and, this is one reason the B-vitamins are considered the energy vitamins.

Your mitochondria uses molecules made from vitamins B2 and B3 to transfer the electrons from the Kreb's cycle to the ETC, since electrons left unprotected are damaging to your cell's components. The ETC moves, or passes these electrons down through a chain of proteins, almost like an electron river in which the proteins are the river banks. The electrons are deposited at the end of the protein chain on the inside of the double membrane in the mitochondria, which creates an electron gradient, like a dam reservoir at the end of a river. The ETC uses five enzyme complexes in its membrane to create this electron reservoir, and also burns oxygen as part of this process. At the end of the ETC is the energy dam, or gate that, when opened, allows the electrons to flow through and, like a dam, transfers the energy to create ATP. Included in the middle of the ETC is the nutrient Coenzyme Q10, which is extremely important in the electron transport and membrane protection. The ETC is also composed of proteins that require iron and sulfur, nutrients you must also obtain from the foods you eat. Iron is present in whole grains, and good food sources of sulfur are the cruciferous vegetables, like broccoli.

Maintaining the structural integrity of your mitochondria is inherently important to your overall health and well-being. If tissues and organs, especially those that have higher energy requirements like the muscle, heart and brain, do not receive adequate supplies of energy, they cannot function properly. Consequently, mitochondrial dysfunction is considered one of the major underlying factors in unhealthy aging and fatigue. Mitochondrial dysfunction is also a major factor in many chronic degenerative diseases, such as congestive heart failure, diabetes mellitus and Parkinson's disease. Along with the inability to produce energy, when damaged, mitochondria can also produce damaging by-products, such as reactive oxygen species, a type of free radical species that can destroy DNA, protein, and fats, promoting further damage.

Nutritional support for healthy energy production includes supporting healthy membranes. In addition, since B-vitamins are so important, adequate intake of vitamins B1, B2, B3, B5 and B6 is extremely important to support energy metabolism. Good sources of these vitamins include whole grains, since the B vitamins are concentrated in the bran of grains. Whole grains are an excellent source of the entire complement of energy-related B-vitamins. Wheat germ is one of the highest sources of tocopherols, the family of vitamin E micronutrients, and brown rice contains oryzanol and ferulic acid, known to be effective antioxidants and health-promoting compounds.
Anatomy of the Animal Cell
Anatomy of the Animal Cell

Mitochondria are oblong shaped organelles that are found in the cytoplasm of every eukaryotic cell. In the animal cell, they are the main power generators, converting oxygen and nutrients into energy.

Mitochondria: Architecture dictates function

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Mitochondria are the cells' power sources. They are distinct organelles with two membranes. Usually they are rod-shaped, however they can be round. The outer membrane limits the organelle. The inner membrane is thrown into folds or shelves that project inward. These are called "cristae mitochondriales". This electron micrograph taken from Fawcett, A Textbook of Histology, Chapman and Hall, 12th edition, 1994, shows the organization of the two membranes.

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The number of mitochondria present in a cell depends upon the metabolic requirements of that cell, and may range from a single large mitochondrion to thousands of the organelles. Mitochondria, which are found in nearly all eukaryotes, including plants, animals, fungi, and protists, are large enough to be observed with a light microscope and were first discovered in the 1800s. The name of the organelles was coined to reflect the way they looked to the first scientists to observe them, stemming from the Greek words for "thread" and "granule." For many years after their discovery, mitochondria were commonly believed to transmit hereditary information. It was not until the mid-1950s when a method for isolating the organelles intact was developed that the modern understanding of mitochondrial function was worked out.
The elaborate structure of a mitochondrion is very important to the functioning of the organelle (see Figure 1). Two specialized membranes encircle each mitochondrion present in a cell, dividing the organelle into a narrow intermembrane space and a much larger internal matrix, each of which contains highly specialized proteins. The outer membrane of a mitochondrion contains many channels formed by the protein porin and acts like a sieve, filtering out molecules that are too big. Similarly, the inner membrane, which is highly convoluted so that a large number of infoldings called cristae are formed, also allows only certain molecules to pass through it and is much more selective than the outer membrane. To make certain that only those materials essential to the matrix are allowed into it, the inner membrane utilizes a group of transport proteins that will only transport the correct molecules. Together, the various compartments of a mitochondrion are able to work in harmony to generate ATP in a complex multi-step process.


Mitochondria provide the energy a cell needs to move, divide, produce secretory products, contract- in short, they are the pwer centers of the cell,. They are about the size of bacteria but may have different shapres depending on the cell type. Mitochondria are membrane-bound organelles, and a double membrane. The outer membrane is smooth. Th einner membrane is fairly smooth. But the inner membrane is highly covoluted, forming folds (cristae). The cristae greatly increase the inner membrane's surface area. It is on these cristae that food (sugar) is combined with oxygen to produce ATP- the primary energy source for the cell.

A mitochondrion is typically long and slender, but it can appear bean-shaped or oval-shaped under the electron microscope. Ranging in size from 0.5 micrometer (0.00005 in) to 1 micrometer (0.0001 in) in length, a mitochondrion has a double membrane that forms a sac within a sac. The smooth outer membrane holds numerous transport proteins, which shuttle materials in and out of the mitochondrion. The region between the outer and inner membranes, which is filled with liquid, is known as the outer compartment. The inner membrane has numerous folds called cristae. Cristae are the sites of ATP synthesis, and their folded structure greatly increases the surface area where ATP synthesis occurs. Transport proteins, molecules called electron transport chains, and enzymes that synthesize ATP are among the molecules embedded in the cristae. The cristae enclose a liquid-filled region known as the inner compartment, or matrix, which contains a large number of enzymes that are used in the process of aerobic respiration.

The chief function of the mitochondria is to create energy for cellular activity by the process of aerobic respiration. In this process, glucose is broken down in the cell's cytoplasm to form pyruvic acid, which is transported into the mitochondrion. In a series of reactions, part of which is called the citric acid cycle or Krebs cycle, the pyruvic acid reacts with water to produce carbon dioxide and ten hydrogen atoms. These hydrogen atoms are transported on special carrier molecules called coenzymes to the cristae.

Mitochondria have significant features that resemble those of prokaryotes, primitive cells that lack a nucleus. Mitochondrial DNA is circular, like the DNA of prokaryotes, and mitochondrial ribosomes are similar to prokaryotic ribosomes. Mitochondria divide independently of the cell through binary fission, the method of cell division typical of prokaryotes.

The prokaryote-like features of mitochondria lead many scientists to support the endosymbiosis hypothesis. This hypothesis states that millions of years ago, free-living prokaryotes capable of aerobic respiration were engulfed by other, larger prokaryotes but not digested, possibly because they were able to resist digestive enzymes. The two cells developed a symbiotic, or cooperative, relationship in which the host cell provided nutrients and the engulfed cell used these nutrients to carry out aerobic respiration, which provided the host cell with an abundant supply of ATP. The engulfed cells evolved into mitochondria, which retain the DNA and ribosomes characteristic of their prokaryotic ancestors.

Mitochondria are the 'power plants' of cells that convert organic materials into energy. Mitochondria have their own DNA
Mitochondria are the 'power plants' of cells that convert organic materials into energy. Mitochondria have their own DNA
Mitochondria are the 'power plants' of cells that convert organic materials into energy. Mitochondria have their own DNA
Their function is essential to efficient energy production. Without them eukaryotic cells would be dependent on anaerobic glycolysis for their ATP. Glycolysis releases very little free energy but in the mitochondria the metabolism of sugars is much more efficient and provides 15 times more ATP than is produced through glycolysis.[5]
Mitochondria take up a large portion of the cytoplasmic volume of eukaryotic cells. They are rod shaped[6]organelles[7] with an inner and an outer membrane. The outer membrane limits the organelle. The inner membrane folds in on itself forming the cristae mitochondriales, giving the appearance of partitions and chambers within the organelle in cross section.[8] The cristae number and shape vary according to the type of tissue and organism. Cristae serve to increase the surface area of the inner membrane.[2].
Mitochondria contain their own genome which is separate and distinct from the genome of the cell.[2] Theoretically, mitochondria may have been separate unicellular organisms at one time and were subsumed in a symbiotic relationship into eukaryotic cells at some point in the evolutionary process.[9] The similarity of genes between the mitochondrial genome and the Rickettsia prowazekii genome suggests this bacteria is the most closely related to mitochondria to date.[10]

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