mitochondrion

Singular of mitochondria, so "one mitochondrion, two mitochondria". A mitochondrion is like a small cell within a cell. Each of the cells in your body, including eggs or spem, contain their own contingent of these little energy transformation factories.

The idea that these organelles are singular, bacteria like entities is valid for some cells, but not all. It is becoming clear that in many eukaryotes they form a continuous Mitochondrial Reticulum(MR) that stretches throughout the cell. Since most images of cell histology have been from slices in the electron microscope, a false image of many separate structures was formed rather than a single unified structure. Only through 3D image reconstruction from many slices of the same cell is it possible to arrenge the components properly. Non-invasive techniques also give a more holistic picture.

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.

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 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

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