One of the defining features of eukaryotic cells is the presence of membrane-enclosed organelles. Two of these organelles, the mitochondria and chloroplast, are unique in that they contain their own genetic material necessary for proper functioning. These organelle genomes are evolutionary relics of free-living bacteria that entered into a symbiotic relationship with a host cell. Through the process of cellular respiration, mitochondria produce about 90 percent of the chemical energy that a cell needs to survive. The discovery that mutations in the mitochondrial genome can cause a variety of human diseases has increased our interest in this "other" human genome.

Organelle Structure and Energy Production

The mitochondria (singular: mitochondrion) are enclosed by two membranes, each a phospholipid bilayer with a unique collection of embedded proteins. The outer membrane is smooth, but the inner membrane contains extensive folds called cristae. The cristae provide a means of packing a...