The mitochondrion (plural: mitochondria) is an organelle that is known as the powerhouse of the cell. It is because it is the organelle that generates most of the cell's supply of adenosine triphosphate (ATP) through the process of cellular respiration. The mitochondrion has outer and inner membranes. The space within the inner membrane is referred to as the mitochondrial matrix. The matrix contains enzymes, mitoribosomes, and the genetic material, i.e. tRNA and DNA. DNA found within the mitochondrion is called mitochondrial DNA (mtDNA) to identify it from the DNA in the nucleus.
The mtDNA is genetically distinct from that in the nucleus. Since a mitochondrion has its own genetic material, and is capable of manufacturing its own RNAs and proteins, it is said to be a semi-autonomous, self-reproducing structure. The entire genetic information in mitochondria is called mitochondrial genome. A human ovum has an average of 200,000 mtDNA molecules. In humans and many other species, the mtDNA is inherited solely from the mother. Nevertheless, there are certain instances that paternal inheritance of mitochondrial genome in humans were described.1
Abbreviation / Acronym:
1 Schwartz, M. & Vissing, J. (2002). "Paternal Inheritance of Mitochondrial DNA". New England Journal of Medicine. 347 (8): 576–580.