Mitochondrial chromosome

Another source of DNA is found in the mitochondria in the cytoplasm of cells (Eig. 2). Unlike nuclear DNA, which only has two copies of each genetic region, mitochondrial DNA is involved in energy production within the cell and can have between 100 and 10,000 copies per cell. Structurally, instead of a linear arrangement of DNA within chromosomes, mitochondrial DNA has a circular structure. Mitochondrial DNA is inherited fl om the mother because it is found in the cytoplasm which comes from the egg (ova). 

Friedreich s ataxia is caused by an intronic triplet repeat expansion. Friedreich s ataxia is an autosomal recessive disorder characterized by progressive ataxia, nystagmus, distal sensory polyneuropathy and corticospinal tract degeneration. It is caused by an unstable expanded GAA repeat in intron 1 of the frataxin gene on chromosome 9ql3. This diminishes expression of frataxin, a mitochondrial iron-storage protein that participates in free radical metabolism [71]. 

Although most DNA is packaged in chromosomes within the nucleus, mitochondria also have a small amount of their own DNA. This genetic material is known as mitochondrial DNA or mtDNA. 

Mitochondria are structures within cells that convert the energy from food into a form that cells can use. Although most DNA is packaged in chromosomes within the nucleus, mitochondria also have a small amount of their own DNA (known as mitochondrial DNA or mtDNA). In some cases, inherited changes in mitochondrial DNA can cause problems with growth, development, and function of the body s systems. These mutations disrupt the mitochondria s ability to generate energy efficiently for the cell. 

Answer E. The 3 to 5 exonuclease activity of DNA pol 8 represents the proofreading activity of an enzyme required for the replication of human chromosomal DNA. DNA pol y (mitochondrial) and DNA pol III (prokaryotic) do not participate in this process, short RNA primers are replaced with DNA during replication, and new DNA strands are always... 

The pattern of inheritance one finds in a family depends on whether the mutant gene is located on an autosome, the X chromosome, or mitochondrial DNA. It also depends on whether the mutant gene is dominant or recessive. 

The circular mitochondrial chromosome encodes 13 of the more than 80 proteins that comprise the major complexes of oxidative phosphorylation as well as 22 tRNAs and 2 rRNAs. Mutations in these genes affect highly aerobic tissues (nerves, muscle), and the diseases exhibit characteristic mitochondrial pedigrees (maternal inheritance). 

Mitochondria, which are cytoplasmic organelles involved in cellular respiration, have their own chromosome, which contains 16,569 DNA base pairs (bp) arranged in a drcalar molecule. This DNA encodes 13 proteins that are subunits of complexes in the electron transport and oxidative phosphorylation processes (see Section 1, Chapter 13). In addition, mitochondrial DNA encodes 22 transfer RNAs and two ribosomal RNAs. 

In the particular case of geographical spreading of single locus mutations on mitochondrial DNA or on Y chromosome [22, 23], we consider a growing population that diffuses slowly in time and assume that the net rate of growth is a linear function of population density, p(n) = — njrioo), where is... 

The nucleus contains almost all of the cell s DNA (around 1% of which is mitochondrial DNA). Together with histones and structural proteins, the nuclear DNA forms the chromatin (see p. 238). it is only during cell division that chromatin condenses into chromosomes, which are also visible with the light microscope. During this phase, the nuclear membrane temporarily disintegrates. 

All eukaryotic cells in our bodies contain the same 23 chromosomes with the same DNA base sequences. The lone differences are the mitochondria. The mitochondria in typical somatic cells contain less than 0.1% of the cell s DNA but in fertilized and dividing egg cells this number is greater. mtDNA is much smaller, often containing fewer than 20,000 base pairs. The value for humans is 16,569 base pairs. The mtDNA is a circular duplex. mDNA codes for the mitochondrial tRNAs and rRNAs but only a fraction of the mitochondrial proteins. Over 95% of the mitochondrial proteins are encoded by nuclear DNA. The mitochondria divide when the cell divides. 

Eukaryotic cells also have organelles, mitochondria (Fig. 24-6) and chloroplasts, that contain DNA. Mitochondrial DNA (mtDNA) molecules are much smaller than the nuclear chromosomes. In animal cells, mtDNA contains fewer than 20,000 bp (16,569 bp in human mtDNA) and is a circular duplex. Each mitochondrion typically has two to ten copies of this mtDNA molecule, and the number can rise to hundreds in certain cells when an embryo is undergoing cell differentiation. In a few organisms (trypanosomes, for example) each mitochondrion contains thousands of copies of mtDNA, organized into a complex and interlinked matrix known as a kinetoplast. Plant cell mtDNA ranges in size from... 

Like bacteria, eukaryotes have several types of DNA polymerases. Some have been linked to particular functions, such as the replication of mitochondrial DNA. The replication of nuclear chromosomes involves DNA polymerase a, in association with DNA polymerase S. DNA polymerase a is typically a multisubunit enzyme with similar structure and properties in all eukaryotic cells. One subunit has a primase activity, and the largest subunit (Afr -180,000) contains the polymerization activity. However, this polymerase has no proofreading 3 —>5 exonuclease activity, making it unsuitable for high-fidelity DNA replication. DNA polymerase a is believed to function only in the synthesis of short primers (containing either RNA or DNA) for Okazaki fragments on the lagging strand. These primers... 

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