The mitochondrial web site : DNA

bours most of the guanine residues, functions as the template for the small (12S) and large (16S) rRNAs, 12 of the polypeptides and 14 of the tRNAs. The light-strand is the template for one polypeptide (ND6) and 8 tRNAs. All the other genes that code for mitochondrial proteins, are nuclear genes.

As a consequence of its endosymbiotic origin, the mitochondria have independent replication, transcription, and translocation systems, which combine the features of prokaryotic and eukaryotic cells.

Each human cell has hundreds of mitochondria and each mitochondrion tens of mtDNA. The human mtDNA is a 16569-nucleotide pair closed circular molecule that codes for 13 essential genes of oxidative phosphorylation, and for 2 structural rRNAs and 22 tRNAs necessary for their expression. The heavy-strand, which har

The mtDNA genome, which is not complexed to histones, is very compact and consequently, lacks introns. Most of the mitochondrial mRNAs lack 5' and 3' translated sequences, starting with the initiation codon and ending with the termination codon. Poly-A tails are added to the mRNAs post-transcriptionally.

Mitochondrial protein synthesis is initiated with formylmethionine and is sensitive to chloramphenicol, the ribosome inhibitor, as the bacterial protein synthesis is. However, mitochondria differ from all other organisms by using a different genetic code, with the codon stop UGA, as well as the UGG used for tryptophan and the arginine codons AGA and AGG for stop codons. Most mitochondrial mRNAs, which contain multiple UGA codons, cannot be translated in the nuclear-cytoplasmic compartment. Hence, this specific mtDNA genetic code confines the mtDNA genes to an expression within the mitochondria.

All the mitochondrial DNA genes encode subunits of the oxidative phosphorylation enzymes, except for the complex II. Complex I consists of approximately 42 polypeptides, seven (ND1, ND2, ND3, ND4L, ND4, ND5, ND6) encoded by the mtDNA; Complex III of about 11 polypeptides, one (cytochrome b) encoded by mtDNA; Complex IV of 13 polypeptides, three (COI, COII, COIII) encoded by the mtDNA; Complex V of 12 polypeptides, two (ATPase 6 and 8) encoded by the mtDNA.