Mitochondria are distinct cellular organelles that oxidise glucose and fatty acids to generate adenosine triphosphate (ATP), the energy carrier in human cells.
It is “self-evident” in some ways, disease is caused by a loss of organisation—by entropy—which is essentially a loss of energy.
Mitochondria contain two plasma membranes, an inner and an outer membrane. One of the key energy-associated pathways, the tricarboxylic acid cycle, is located in the mitochondrial matrix, while the final common pathway for energy production, the electron transport chain, is located on the inner mitochondrial membrane.
The integrity of mitochondrial membranes is critical to cell function and energy metabolism. This membrane is the frontier between cell survival and death.
The number of mitochondria in each cell depends on the cellular energy demands. Low energy cells, such as skin cells, have fewer mitochondria, while cells that require high energy demands, such as muscle, brain, and gastrointestinal (GI) cells possess many mitochondria.
Mitochondria are the only organelle in human cells with their own genome primarily derived from the maternal parent. Electron transport chain enzymes are coded by both mitochondrial DNA and nuclear DNA while other mitochondrial enzymes are coded by nuclear DNA.
At the biochemical level fatigue is related to the metabolic energy available to tissues and cells, mainly through mitochondrial electron transport. Electron transport is directly linked to functional, intact inner mitochondrial membranes. Thus the integrity of mitochondrial membranes is critical to cell function and energy metabolism.
In addition to energy production, the mitochondria are intimately involved in programmed cell death (apoptosis), calcium homeostasis, synaptic plasticity and neurotransmitter release.
This places mitochondria at the cross roads of bioenergetics metabolism, cell death signalling and the innate and adaptive immune system.
