ABSTRACT
Mitochondria are the central integrators of intermediary metabolism. Mitochondria vary in size and shape in different cell types. Regardless of size and shape, this organelle consists of two membranes separated by an inner membrane space. Electrons shuttled into the mitochondrial compartment by the nicotinamide dinucleotide-linked and flavinadinine dinucleotide-linked shuttles are transported through inner membrane-bound respiratory chain enzyme complexes and joined to oxygen to form water. Mitochondrial disease can also result from depletion, deletions, and duplications of the mitochondrial genome. Another feature of mitochondrial genetics is the threshold effect: Clinical disease occurs when mitochondrial energy output falls below some minimum threshold level. Mitochondrial gene expression can be regulated by growth and development in a tissue-specific manner. In addition to regulation during mitochondrial proliferation and differentiation, mitochondrial transcription may also be directly regulated by hormone receptors. While mitochondria do not contain histones per se they do contain histone-like proteins.
