Mitochondria have roles beyond energy production, including control of gene expression and neurotransmitter production.

“What I'm hearing is that mitochondria, in addition to being important sources of energy production and output in cells-- which, of course, they are-- probably have other roles. Maybe someday, what we call mitochondria will actually be two or three different little subcellular or organelles. There may be little bits in there that are controlling gene expression and little bits in there that are controlling neurotransmitter production.”