Mitochondrial DNA

Mitochondrial DNA (mtDNA)

• It is a separate genome located in the cytoplasm of nearly all eukaryotic cells
• Is closede circular, double-stranded, and composed of heavy (H) and light (L) chains or strands.
• Contains 16,569 bp.
• Encodes 13 protein subunits of the respiratory chain (of a total of about 67) –

1. Seven subunits of NADH dehydrogenase (complex I) and Cytochrome b of complex III
2. Three subunits of cytochrome oxidase (complex IV)
3. Two subunits of ATP synthase

• Encodes large (16S) and (12S) mt ribosomal RNAs
• Encodes 22 mt tRNA molecules
• Genetic code differs slightly from the standard code –

1. UGA (standard stop codon) is read as Trp.
2. AGP and AGG (standard codons for Arg) are read as stop codons,

• Contains very few untranslated sequences.
• Nemaline myopathy results due to mutations in mt- DNA
• Heteroplasmy is the presence of mixture of more than one type of an organelle genome (mt- DNA) within a cell or individual.
• High mutation rate (5 to 10 times that of nuclear DNA).
• Comparisons of mtDNA sequences provide evidence about evolutionary origins of primates and other species.
• High mutation rate occurs due to point mutation and large scale rearrangements.
• mitochondrial DNA contains no (or very few) introns (i.e. untraslated sequences).

Mitochondrial DNA is always maternally inherited.

1. Important mitochondrial diseases are mitochondrial encephalomyopathy with lactic aciilosis and stroke like episodes (MELAS),
2. leber hereditary optic neuropathy, myoclonic epilepsy with ragged-red fibers, leigh syndrome, Pearson syndrome, kearns-sajre syndrome,
3. chronic progressive external ophthalmoplegia and NARP (neurogenic weakness with ataxia & retinitis pigmentosa).

• All children from affected mother will inherit the disease but it will not be transmitted from an afiected father to his children

Don’t Forget to Solve all the previous Year Question asked on Mitochondrial DNA