115
complications neurogenerative disorders such as Parkinson’s disease and even the aging
process. For many physicians, however, mitochondrial diseases remain at the bottom of
a long list of differential diagnoses.9 The reason is likely due to the fact that mitochondria
are the products of two genomes (mitochondrial and nuclear), and as noted below, the
biochemical mechanisms involved in the generation of ATP are extremely complex.
Derivation
Mitochondria are believed to be descendants of bacteria that invaded early eukaryotic
cells and stayed on in a symbiotic relationship. (Eukaryotic cells have a true nucleus.)
Mitochondria may have started off as free-living prokaryotes (single-celled organisms
without a nucleus) that were engulfed by the ancestors of modern nucleated cells two
billion years ago.10 Recent research suggests that the acquisition of mitochondria was far
more important than simply plugging an efficient power supply into an already com-
plicated cell with a nucleus brimming with genes. It was the single event that made the
evolution of complex eukaryotic cells possible. If the mitochondrial merger had not hap-
pened, we would likely not be here today, and neither would any other form of intelligent
or genuinely multicellular life.11 (There is at least one exception, however, the single-celled
parasite known as giardia. This is the organism responsible for giardiasis, a major cause
of diarrhea. Even though giardia belongs to the eukaryotes, the domain that includes all
plants and animals, it lacks mitochondria. Even stranger, perhaps, is that each giardia cell
possesses two nuclei instead of just one.12)
The greatest boost to the endosymbiotic (one symbiotic organism living inside the
other) origin of mitochondria came from the discovery of DNA in mitochondria and from
the generalization that all mitochondria in all eukaryotes contained DNA. Mitochondria
contain genes that are bacterial and contained on a single, circular chromosome.
Mitochondrial genes are passed on to the next generation only in the egg cell, not in the
sperm, and thus we can trace our genetic inheritance back into the deep mists of time.
Mitochondrial Eve, the mother of all mothers, is thought to have lived in Africa more than
170,000 years ago.13
Description and Function
Mitochondria are described as subcellular organelles that coordinate numerous metabolic
reactions, including those of the respiratory complexes that produce the ATP that powers
cellular reactions. The mitochondria within a typical cell undergo continual cycle fusion
and fission. As mentioned earlier, the cells that make up our bodies contain numerous
mitochondria the exact number depends upon the metabolic demand of that particular
cell. Metabolically active cells, such as those of the liver, kidneys, muscles and brain, have
hundreds or thousands of mitochondria, comprising up to about 40% of the cytoplasm.14
Mitochondria are varied in structure, ranging from small, spherical particles to long,
interconnected filaments. They take many twisted and contorted shapes. Mitochondria are
generally a few thousandths of a meter in length (1–4 microns) and about a half micron
in diameter. Each one is a chemical factory processing more than 700 different chemical
substances in long, interweaving assembly lines along the surface of its intricately folded
membranes. Many fuel sources are utilized in the production of ATP, which powers
almost every activity of the cell and organism. ATP is used to build complex molecules,
contract muscles and generate pulses in nerve cells, among a host of other tasks.15 ATP has
another important role as a signaling molecule that allows cells and tissues throughout
the body to communicate with one another. Energy is liberated from the ATP molecule
by a reaction that removes one of its three phosphate-oxygen groups, leaving adenosine
diphosphate (ADP). Then the ADP is recycled in the mitochondria, where it is recharged
using photons derived from such raw materials as glucose that have undergone several
processing steps, and comes out again as ATP. The enormous amount of activity that goes
Mitochondria and Mitrochondrial Diseases—Badly Kept Secrets
complications neurogenerative disorders such as Parkinson’s disease and even the aging
process. For many physicians, however, mitochondrial diseases remain at the bottom of
a long list of differential diagnoses.9 The reason is likely due to the fact that mitochondria
are the products of two genomes (mitochondrial and nuclear), and as noted below, the
biochemical mechanisms involved in the generation of ATP are extremely complex.
Derivation
Mitochondria are believed to be descendants of bacteria that invaded early eukaryotic
cells and stayed on in a symbiotic relationship. (Eukaryotic cells have a true nucleus.)
Mitochondria may have started off as free-living prokaryotes (single-celled organisms
without a nucleus) that were engulfed by the ancestors of modern nucleated cells two
billion years ago.10 Recent research suggests that the acquisition of mitochondria was far
more important than simply plugging an efficient power supply into an already com-
plicated cell with a nucleus brimming with genes. It was the single event that made the
evolution of complex eukaryotic cells possible. If the mitochondrial merger had not hap-
pened, we would likely not be here today, and neither would any other form of intelligent
or genuinely multicellular life.11 (There is at least one exception, however, the single-celled
parasite known as giardia. This is the organism responsible for giardiasis, a major cause
of diarrhea. Even though giardia belongs to the eukaryotes, the domain that includes all
plants and animals, it lacks mitochondria. Even stranger, perhaps, is that each giardia cell
possesses two nuclei instead of just one.12)
The greatest boost to the endosymbiotic (one symbiotic organism living inside the
other) origin of mitochondria came from the discovery of DNA in mitochondria and from
the generalization that all mitochondria in all eukaryotes contained DNA. Mitochondria
contain genes that are bacterial and contained on a single, circular chromosome.
Mitochondrial genes are passed on to the next generation only in the egg cell, not in the
sperm, and thus we can trace our genetic inheritance back into the deep mists of time.
Mitochondrial Eve, the mother of all mothers, is thought to have lived in Africa more than
170,000 years ago.13
Description and Function
Mitochondria are described as subcellular organelles that coordinate numerous metabolic
reactions, including those of the respiratory complexes that produce the ATP that powers
cellular reactions. The mitochondria within a typical cell undergo continual cycle fusion
and fission. As mentioned earlier, the cells that make up our bodies contain numerous
mitochondria the exact number depends upon the metabolic demand of that particular
cell. Metabolically active cells, such as those of the liver, kidneys, muscles and brain, have
hundreds or thousands of mitochondria, comprising up to about 40% of the cytoplasm.14
Mitochondria are varied in structure, ranging from small, spherical particles to long,
interconnected filaments. They take many twisted and contorted shapes. Mitochondria are
generally a few thousandths of a meter in length (1–4 microns) and about a half micron
in diameter. Each one is a chemical factory processing more than 700 different chemical
substances in long, interweaving assembly lines along the surface of its intricately folded
membranes. Many fuel sources are utilized in the production of ATP, which powers
almost every activity of the cell and organism. ATP is used to build complex molecules,
contract muscles and generate pulses in nerve cells, among a host of other tasks.15 ATP has
another important role as a signaling molecule that allows cells and tissues throughout
the body to communicate with one another. Energy is liberated from the ATP molecule
by a reaction that removes one of its three phosphate-oxygen groups, leaving adenosine
diphosphate (ADP). Then the ADP is recycled in the mitochondria, where it is recharged
using photons derived from such raw materials as glucose that have undergone several
processing steps, and comes out again as ATP. The enormous amount of activity that goes
Mitochondria and Mitrochondrial Diseases—Badly Kept Secrets