The most prominent roles of mitochondria are production of adenosine triphosphate (ATP) and regulation of cellular metabolism.  Mitochondria contain their own DNA (mtDNA), which is a 16.5-kb circular double-stranded DNA (dsDNA), encoding 13 polypeptides, 22 transfer RNA (tRNA), and two ribosomal RNA (rRNA).  The 13 polypeptides are subunits of a series of large enzyme complexes located in the inner mitochondrial membrane necessary for ATP production via oxidative phosphorylation.  Of the 22 mitochondrial tRNAs, the single most used tRNA (~14.9%) for mitochondrial protein synthesis is tRNALeu (CUN).  Mitochondrially encoded tRNA leucine 2 (CUN), also known as MT-TL2, is a small 71 nucleotide RNA.  It transfers leucine to a growing polypeptide chain at the ribosome site of protein synthesis during translation.

mtDNA is multicopy and maternally inherited.  Mutations within mtDNA are associated with various disease phenotypes, such as sensorineural hearing impairment, mitochondrial Leber's hereditary optic neuropathy, and mitochondrial encephalopathy, lactacidosis, and stroke-like episodes syndrome (MELAS).