Mitochondrial gene

The majority of the peptides in mitochondria (about 54 out of 67) are coded by nuclear genes. The rest are coded by genes found in mitochondrial (mt) DNA. Human mitochondria contain two to ten copies of a smaU circular double-stranded DNA molecule that makes up approximately 1% of total ceUular DNA. This mtDNA codes for mt ribosomal and transfer RNAs and for 13 proteins that play key roles in the respiratory chain. The linearized strucmral map of the human mitochondrial genes is shown in Figure 36-8. Some of the feamres of mtDNA are shown in Table... 

Adapted from Harding AE Neurological disease and mitochondrial genes.Trends Neurol Sci 1991 14 132. 

Disorders of mitochondrial oxidative phosphorylation Proteins encoded by mitochondrial genes Proteins encoded by nuclear genes... 

Hyman, B.C. and Beck Azevedo, J.L. (1996) Similar evolutionary patterning among repeated and single copy nematode mitochondrial genes. Molecular Biohgy and Evolution 13, 221—232. 

Sukhdeo, S.C., Sukhdeo, M.V.K., Black, M.B. and Vrijenhoek, R.C. (1997) The evolution of tissue migration in parasitic nematodes (Nematoda Strongylida) inferred from a protein-coding mitochondrial gene. Biological Journal of the Linnean Society 61, 281—298. 

Weissig V, Torchihn VP. Mitochondriotropic cationic vesicles a strategy towards mitochondrial gene therapy. Curr Pharm Biotechnol 2000 l(4) 325-346. 

Weissig V, Torchihn VP. Towards mitochondrial gene therapy DQAsomes as a strategy. J Drug Target 2001 9(1) 1-13. 

Mitochondrial diseases are often expressed as neuropathies and myopathies because brain and muscle are highly dependent on oxidative phosphorylation. Mitochondrial genes code for some of the components of the electron transport chain and oxidative phosphorylation, as well as some mitochondrial tRNA molecules. 

Answer B, Inheritance only from affected females strongly suggests a defect in a mitochondrial gene. Defects in mitochondrial gene expression phenotypkaUy present as problems in nerves and/or muscles, tissues with high aerobic metabolism. 

Mitochondrial genes are not known to affect the expression of Marfan syndrome (choice C). 

Mitochondria have their own limited genome, the remnants of the genome of the microorganism from which they are derived. Mitochondrial genes code for 13 proteins that are synthesized in the mitochondria and are critical parts of the mitochondrial electron transport chain. 

It is important to emphasise that only the head of the sperm enters, so that it is only the nuclear genetic material that enters the ovum, that is, the genetic material in the mitochondria of the sperm does not enter the ovum and hence it does not appear in the zygote. Consequently, mitochondrial genes are inherited only from the mother. This has implications for some mitochondrial diseases (Chapter 9). 

Bonawitz, N. D., Chatenay-Lapointe, M., Pan, Y., and Shadel, G. S. (2007). Reduced TOR signalling extends chronological life span via increased respiration and upregulated mitochondrial gene expression. Cell Metab. 5, 265-277. 

The code is not entirely universal there are minor differences between the codes used for synthesis of proteins encoded by nuclear versus mitochondrial genes of human cells. 

Adams KL, Palmer JD (2003) Evolution of mitochondrial gene content gene loss and transfer to the nucleus. Mol Phylogenet Evol 29 380-395 Adams KL, Daley DO, Qiu YL, Whelan J, Palmer JD (2000) Repeated, recent and diverse transfers of a mitochondrial gene to the nucleus in flowering plants. Nature 408 354-357... 

Choi C, Liu Z, Adams KL (2006) Evolutionary transfers of mitochondrial genes to the nucleus in the Populus lineage and coexpression of nuclear and mitochondrial Sdh4 genes. New Phytol 172 429-439... 

Roger AJ, Clark CG, Doolittle WF (1996) A possible mitochondrial gene in the early-branching amitochondriate protist Trichomonas vaginalis. Proc Nad Acad Sci USA 93 14618-14622... 

Spironucleus barkhanus mitochondrial genes in genome Horner and Embley 2001... 

Trimastix pyriformis EM, mitochondrial genes 2D, 3D O Kelly et al. 1999, Brugerolle... 

Mitochondrial Genes Their Origin and the Effects of Mutations 719... 

Mutations in Mitochondrial Genes Cause Human Disease... 

A growing number of human diseases can be attributed to mutations in mitochondrial genes. Many of these diseases, those known as the mitochondrial encephalomyopathies, affect primarily the brain and skeletal muscle (both heavily dependent on an abundant supply of ATP). These diseases are invariably inherited from the mother, because a developing em-... 

TABLE 19-6 Respiratory Proteins Encoded by Mitochondrial Genes in Humans... 

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