Mitochondrial Genome

Cecilia Saccone, University of Bari, Bari, Italy

Published online: February 2011

DOI: 10.1002/9780470015902.a0005069.pub2

Mitochondria are cytoplasmic organelles present in all eukaryotic cells that are able to respire. They possess their own genetic system whose size and organisation are quite variable in plants, protists and fungi. A certain degree of structural variability is observed also in Metazoa, whereas mitochondrial deoxyribonucleic acid (mtDNA) is rather small but constant in vertebrate cells (about 17 kb). The genetic content and organisation of human mtDNA is very similar in all vertebrates. It consists of two ribosomal ribonucleic acid (RNA) genes, 13 protein-coding genes and 22 transfer RNAs. All other mitochondrial products are coded by nuclear DNA and transported into the mitochondrion. Mitochondrial genetic system has a uni-directional way of inheritance, and it is present in cell in a multicopy state. mtDNA replication, transcription and translation are also very peculiar. Evolutionary origin of mitochondria has been described through the endosymbiotic theory.

Key Concepts:

  • Mitochondria are eukaryotic cell organelles with their own genome.
  • Mitochondrial genome shows great structural variability in most eukaryotic taxa but are quite stable for content and organisation in Metazoans.
  • mtDNA has a poor gene content; mitochondrial protein genes encode for respiratory chain subunits, fundamental for cell energy production.
  • The mitochondrial genome has bacterial origin, with several peculiar features about its replication and expression.
  • mtDNA is a multicopy genome that is uni-parentally transmitted and does not undergo recombination.
  • Evolution of mtDNA (within Metazoa) is lineage-specific.

Keywords: organelle DNA; oxidative phosphorylation; energy production; D loop; endosymbiosis; uni-directional inheritance; recombination; selection; mutation; phylogenetic inference

Figure 1. Schematic representation of the mitochondrion with details of the inner membrane and its respiratory complexes (I–IV). Mitochondria are formed by two membranes, an outer membrane having mainly permeability properties and an inner membrane where electron transport and oxidative phosphorylation occur. The inner space, called matrix, contains metabolic enzymes, the mitochondrial DNA, and the genetic apparatus for its replication and expression. The electron (e–) flux through the respiratory complexes results in a drop in the free energy, which is used to pump protons (H+) from the matrix to the intermembrane space. The energy conserved into this proton gradient is used to promote adenosine 5¢-triphosphate (ATP) synthesis by ATP synthase through the inversion of proton flux from intermembrane space to matrix. Abbreviations: ADP, adenosine 5¢-diphosphate; NAD+, oxidised form of nicotinamide–adenine dinucleotide; NADH, reduced form of nicotinamide–adenine dinucleotide and QU, ubiquinone.
Figure 2. Organisation of human mitochondrial DNA. The two strands are called heavy (H) and light (L) according to their isopycnic sedimentation in a cesium chloride gradient. Gene distribution between the two strands and the main regulatory regions is indicated. The protein-coding genes are ATP6, ATP8, ATPase subunits; CO I, II, III, cytochrome c oxidase subunits; Cytb, cytochrome b; 1, 2, 3, 4, 4L, 5, 6, NADH dehydrogenase subunits; 12S, 16S rRNAs, small and large ribosomal subunits RNA; A, alanine; C, cysteine; D, aspartic acid; E, glutamic acid; F, phenylalanine; G, glycine; H, histidine; I, isoleucine; K, lysine; L, leucine; M, methionine; N, asparagine; OL , L strand replication origin; OH, H strand replication origin; P, proline; Q, glutamine; R, arginine; S, serine; T, threonine; V, valine; W, tryptophan and Y, tyrosine transfer RNA genes. In the expanded D loop region – CSB, conserved sequence box; ETAS, extended termination-associated sequences; HSP, H strand promoter; LR and SR, short and long repeats; LSP, L strand promoter; the conserved central domain (black bar), the RNA primer (grey) and the RNA/DNA transition are indicated.
Figure 3. Schematic representation of the asymmetric replication (a) and of the stable processed RNAs and precursor species (b) of the mammalian mitochondrial genome (black circle represents the long policistronic transcript for H strand; short black lines indicate the mature transcripts).
Figure 4. Maternal inheritance of mitochondrial DNA. The small black arrow indicates the common ancestor of the whole lineage derived from it.
Figure 5. Graphical representation of GC skew and GC content calculated on the whole mitochondrial genome in five mammalian orders and Homo sapiens.
Figure 6. Nucleotide substitution rate of the different mitochondrial DNA functional regions in mammals.
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Related Sub-Topics:

Cell Compartments and Cellular Organelles | DNA Structure and Function | Nonchromosomal DNA | Evolution of Coding and Functional Modules
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Article Title: Mitochondrial Genome
 
How to Cite close
Saccone, Cecilia(Feb 2011) Mitochondrial Genome. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0005069.pub2]