| MadSci Network: Cell Biology |
The size of the mitochondrial genome varies among eukaryotic kingdoms: in protozoa, it's 20-40 kb (kilobases, thousands of base pairs); in animals, it's 16-19 kb; in fungi, it's 15-80 kb; and in plants, it's anywhere from 16 kb (in algae) to 2500 kb (in some angiosperms). In the case of mammals, the mitochondrial genome is around 16, 500 base pairs in length, compared to the human genome which is 3 billion base pairs (3 Gb), about 200, 000 times larger. The two chief differences between mitochondrial DNA and nuclear DNA are that the mitochondrial genome is contained on a single circular chromosome rather than multiple linear chromosomes, and that there are 5 to 10 copies per mitochondrion of the mitochondrial chromosome rather than just two copies of each chromosome in the nucleus. With hundreds to thousands of mitochondria per cell, the total mitochondrial DNA accounts for about one percent of the total DNA of the cell. There are also differences in the replication and transcription of mitochondrial DNA, which have prompted most biologists to view these organelles as having evolved from endosymbiotic bacteria (bacteria that live inside other organism's cells and serve some function, like the Rhizobacteria that enter the root cells of bean plants and allow them to live in nitrogen-poor soil), which became an integral part of eukaryotic life before the evolution of higher organisms.
This and more information on mitochondria can be found in:
Molecular Biology of the Cell by Bruce Alberts, et al. - 2nd ed., Garland Publishing, Inc., New York & London, 1989.
(I think there is a third edition out now); or any other biology textbook.
Try the links in the MadSci Library for more information on Cell Biology.