Figure 2

(a) Sequence organization of the mammalian mtDNA. Colors indicate mtDNA-encoded subunits for respective electron transport complexes, ATP synthase, tRNAs, and rRNAs. ATPase 6 and 8 subunits overlap in sequence. The origins of heavy-strand (guanosine rich) and light-strand DNA synthesis are indicated by O_H and O_L, respectively. Transcriptional promoters for the heavy and light strands are represented by P_H and P_L, respectively. The D-loop (displacement loop) is an ∼1 kb non-coding region within the mtDNA. The mtDNA genetic code is highly degenerate, so that only 22 are required for protein translation. When uridine is in the wobble position, all four members of a codon family can be read by one mitochondrial tRNA, whereas pairs of codons can be read when guanine or uridine is in the wobble position. Hence, eight mitochondrial tRNAs recognize four member codon families, while 14 tRNAs recognize codon pairs. (b) Table presenting the number of mtDNA and nDNA-encoded subunits for each electron transport complex (I–IV) and ATP synthase (V) in the mammalian mtDNA. (c) Table summarizing the known (or putative) function of each of the mtDNA-encoded genes.