mitochondria

"This is a song about the fucking mitochondria, the so-called factory of the cell, damn right it's a factory... they're holding an industrial revolution in your own body and you don't even get paid! Billions of cells working 24 hours a day, all being exploited by the mitochondria factory owners, making you slave and ripping you off, and taking away your rights! Mitochondria fucking suck!"

"One two three four!"

Mitochondria are self-replicating double-walled organelles in all eukaryotic cells. These cells have between 1 and 10,000 mitochondria, but most cells average around 200. The typical liver cell has over 1,000 mitochondria.

Some people have theorized that the mitochondria was a primitive independent life form which formed a symbiotic relationship with a host cell, and have been an important part of eukaryotic cells ever since.

Mitochondria, the plural of mitochondrion, are organelles which function as the powerhouse of the cell. The Krebs Cycle takes place in it, producing ATP.

They are oval, look like little pills, but have a large surface area within by its many folds to carry out cellular respiration and combine oxygen with food to get energy and utilitze ATP-ADP reactions.A cell typically has dozens of them, and muscle and heart cells have thousands of them.

Scientists suspect that mitochondria were once small microorganisms about 3.5 billion years ago and were absorbed into mammal cells and became symbiotes. This explains why they have their own 37 genes of DNA.

What makes them so special today is that they actually have their own set of mitochondrial DNA, inherited from the mother's mitochondria. This is sort of complicated, and still partly theory, but the sperm and egg have their own mitochondria. When they combine, the egg gives off an enzyme to degrade the male mitochondria. (see targeting sperm mitochondria for destruction) In some cases the male mitochondria is present, and may be responsible for many diseases where the mitochondria are faulty. fautly Mitochondria DNA can deprive the nucleus of energy and lead to cancer and other diseases.

In 1988, Dr. Wallace and Dr. Emory Brown made history when they discovered a genetic mitochondrial disease passed from mother to son. Known as Leber's hereditary optic neuropathy (LHON), the condition is marked by rapid vision loss, heart rhythm abnormalities, dementia, epilepsy, and intermittent spastic muscle action. It usually strikes males between 20 and 24 and is invariably fatal.

The last paragraph taken from Newsday August 15, 2000

The purpose of the Krebs cycle is to generate nadh in order to power the electron transport chain. Up until this point, respiration has produced relatively small amounts of ATP. Now we finally get the big payoff. Hydrogen ions from NADH are transferred across from the interior of the mitochondria to the external matrix, generating a potential difference across the internal membrane. Why is this good? Potential difference means electrical current. We get a flow of electrons across the internal membrane which are used to power ATP synthase. Eventually the electrons become reunited with hydrogen ions and we use oxygen as an acceptor (the reason for the requirement of oxygen in aerobic respiration) which produces water which is nice and easy to deal with.

The increased ability to produce energy that mitochondria provide is probably one of the reasons for us eukaryotes being up here and prokaryotes never getting round to discovering fire, inventing the wheel, forming civilisation, that sort of thing.

Introduction

Mitochondria are organelles found in nearly all eukaryotic cells. Their primary function is the synthesis of ATP in aerobic respiration. They are also involved in lipid synthesis.

Structure

Mitochondria are approximately 7 micrometres long and consist mainly of a double phospholipid envelope, the inner membrane of which is infolded into projections called cristae. The middle of the mitochondrion, called the matrix, contains small amounts of mitochondrial DNA and ribosomes. There are usually several mitochondria in each cell, depending on how much energy the cell requires.

Function

The primary function of the mitochondrion is the second half of the respiration process, where glucose and other sugars are converted into ATP, the body's "energy currency". Respiration can be divided into four main parts: glycolysis, the Krebs cycle, oxidative phosphorylation and the synthesis of ATP. The Krebs cycle, oxidative phosphorylation, and the synthesis of ATP all occur in the mitochondria. In anaerobic respiration only glycolysis occurs and mitochondria are not necessary.

The Krebs cycle:

The Krebs cycle is the process where the pyruvate created by glycolysis is broken completely down into carbon dioxide. It occurs in the matrix of the mitochondria. Although some ATP is created here, most of the energy from aerobic respiration is actually produced by the hydrogen atoms, which are removed from the cycle by hydrogen carrier molecules such as NAD or FAD, and enter the oxidative phosphorylation step.

Oxidative phosphorylation

The hydrogen atoms taken from the Krebs cycle are taken to the inner membrane of the mitchondrial envelope, where the hydrogen atoms are split into electrons and hydrogen ions. The electrons are passed along a chain of electron carriers (usually cytochromes) until the are recombined with the hydrogen ion and oxygen to create water. Energy is produced by the electron transfer chain which is used to pump hydrogen ions into the inter-membrane space for the synthesis of ATP.

Synthesis of ATP

Although some ATP has been produced by the earlier reactions, most of the ATP is produced by the movement of hydrogen ions from the intermembrane space, down the concentration gradient, into the matrix. The hydrogen ions can only pass through a protein in the membrane called ATP synthase, which uses the energy of the movement of hydrogen ions to add a phosphate group to ADP to create ATP.

Endosymbiotic theory

Several features of mitochondria have led to the endosymbiotic theory, which states that they were once separate simple single-celled organisms, which were completely absorbed by larger organisms, which then harnessed it's ability to aerobically respire to gain an evolutionary advantage. Evidence for this theory includes the presence of separate DNA and ribosomes in the mitochondria

Mitochondria are organelles found in eukaryotes which are responsible for the oxidation of energy-rich substances. They are oval and have a diameter of approximately 1.5 micrometers and width of 2 to 8 micrometers.

Mitochondria have their own DNA and are thought to have evolved when an early eukaryote engulfed some primitive bacteria, but instead of digesting them, harnessed them to produce energy. Human children inherit their mothers' mitochondria, and thus mitochondrial DNA has been useful in tracing human lineages.

Compare chloroplast.

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From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. Used with permission. For further information see the BioTech homenode.

According to the endosymbiont hypothesis, mitochondria and chloroplasts are the evolutionary descendants of free-living prokaryotes, which during evolution have been stripped of practically all functions except those related to energy transduction. Some prokaryotic organisms have features similar to those of energy-transducing organelles: Paracoccus denitrificans, an aerobic bacterium, has an electron transport chain like that in mitochondria, and Prochloron, a green photosynthetic bacterium, has a light trapping system (with chlorophyll b) like that found in chloroplasts in higher plants.

It is envisaged that the modern eukaryotic animal cell arose from the emergence of a nucleated cell dependent on glycolytic fermentation for its ATP supply and separately from the emergence of a nucleated bacterial cell, possessing a respiratory chain and therefore a more efficient method of producig ATP. Early in the evolutionary timescale, the nucleated cell either absorbed or was invaded by the bacterial cell. Initially, a stable endo-symbiotic relationship was established which conferred advantages over the free living nucleated cells or anucleated cells. Such an arrangement is seen even today in the giant amoeba Pelomyxa palustris, which lacks mitochondria but contains respiring endosymbiotic bacteria. During the evolution of eukaryotic cells the nuclear genome has absorbed most of the genome of the anucleated organism. The plant cell is probably a descendant of this cell, which some time early on in evolution, absorbed a second prokaryotic cell capable of carrying photophosphorylation.