Mitochondrial and Chloroplast DNA

Microbiology has undergone an explosion of discovery...into realms that are as bizarre as anything appearing...in novels. 

DNA in the chloroplasts of plants is transmitted from one generation to the next through the egg (Juniper, 2007), similarly to the DNA of mitochondria. The DNA for both of these structures is circular, as it is in prokaryotes. Thus, for higher level plants that depend on photosynthesis to fix carbon from atmospheric carbon dioxide (and thus contain chloroplasts), there are three independent DNA stores in the cell in the chloroplast, in the mitochondria, and in the nucleus. 

Female inheritability can be traced through mitochondrial DNA because mitochondria come only from egg cells. Thus, lineage can be traced by comparing mitochondrial DNA from one generation to the next. The number of generations, and thus the time between two relatives, can be estimated by assuming a certain rate of DNA mutation and looking at DNA differences. 

Male inheritability can be traced through the Y sex chromosome. Each male somatic cell contains two sex chromosomes, an X and a Y (figure). Females have two Xs. 

Images of X and Y sex chromosomes. The Y chromosome is much shorter than the X chromosome, and is carried only by males. 

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The genetic information (DNA) and the protein-synthesizing capability of mitochondria and chloroplasts are similar to those of prokaryotes. For example, both mitochondrial and chloroplast DNA are circular and naked (i.e., not com-plexed with histone proteins as nuclear DNA is). (There is insufficient genetic information on these chromosomes to account for all organelle components. However, the nuclear genes that are responsible for synthesis of mitochondrial components resemble prokaryotic genes.)... 

These commonalities between mitochondria, chloroplasts, and bacteria undoubtedly have an evolutionary origin. In bacteria both photosynthesis and oxidative phosphorylation occur on the plasma membrane. Analysis of the sequences and transcription of mitochondrial and chloroplast DNAs (Chapters 10 and 11) has given rise to the popular hypothesis that these organelles arose early in the evolution of eukaryotic cells by endocytosis of bacteria capable of oxidative phosphorylation or photosynthesis, respectively (Figure 8-3). According to this endosymbiont... 

We conclude this chapter with a brief discussion of transcription Initiation by the other two eukaryotic nuclear RNA polymerases, Pol 1 and Pol 111, and by the distinct polymerases that transcribe mitochondrial and chloroplast DNA. Although these systems, particularly their regulation, are less thoroughly understood than transcription by RNA polymerase 11, they are also fundamental to the life of eukaryotic cells. 

Mitochondrial and Chloroplast DNAs Are Transcribed by Organelle-Specific RNA Polymerases... 

Demesure, B., Sodzi, N., and Petit, R.J., A set of universal primers for amplification of polymorphic noncoding regions of mitochondrial and chloroplast DNA in plants, Molec. Ecol., 4, 129, 1995. 

Ribosomes, the intracellular particles on which proteins are assembled, are highly complex and dynamic entities. The structural framework of ribosomes is provided by ribosomal RNA (rRNA) molecules with which many proteins are associated (summarized in Capowski and Tracy, 2003). Homologous rRNA genes occur in all prokaryotes and eukaryotes. The mitochondrial and chloroplast rRNA genes in eukaryotes clearly have prokaryote affinities (Pace et ai, 1986). The genomic DNA from which ribosomal genes are transcribed, along with any associated spacers, is collectively termed ribosomal DNA (rDNA). Sequences and other data from rDNA and its products,... 

Both mitochondrial and chloroplast genomes are believed to have evolved through endosymbiosis. This model of organelle evolution proposes that eukaryotic cells captured bacteria that later provided the function of mitochondria and chloroplast. Phylogenetic studies based on DNA sequence analysis suggest that mitochondria and chloroplasts evolved separately from eubacterial lineages... 

The molecular mechanisms by which ATP is formed in mitochondria and chloroplasts are very similar, as explained in Chapter 8. Chloroplasts and mitochondria have other features in common both often migrate from place to place within cells, and they contain their own DNA, which encodes some of the key organellar proteins (Chapter 10). The proteins encoded by mitochondrial or chloroplast DNA are synthesized on ribosomes within the organelles. However, most of the proteins in each organelle are encoded in nuclear DNA and are synthesized in the cytosol these proteins are then incorporated into the organelles by processes described in Chapter 16. 

All mtDNAs and chloroplast DNAs appear to encode rRNAs, tRNAs, and some of the proteins Involved In mitochondrial or photosynthetic electron transport and ATP synthesis. 

As discussed in Chapter 10, mitochondria and chloroplasts probably evolved from bacteria that were endocytosed into ancestral cells containing a eukaryotic nucleus. In modern-day eukaryotes, both organelles contain distinct circular DNAs that encode some of the proteins essential to their specific functions. The RNA polymerases that transcribe mitochondrial (mt) DNA and chloroplast DNA are similar to polymerases from bacteria and bacteriophages. 

Mitochondria and chloroplasts contain multiple copies of double-stranded circular genomes that encode genes required for organelle-specific functions. The complete DNA sequence of representative mitochondrial and chloroplast genomes is known and has been used to characterize genetic mutations. 

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... 

Mitochondrial DNA codes for the mitochondrial tRNAs and rRNAs and for a few mitochondrial proteins. More than 95% of mitochondrial proteins are encoded by nuclear DNA. Mitochondria and chloroplasts divide when the cell divides. Their DNA is replicated before and during division, and the daughter DNA molecules pass into the daughter organelles. 

DNA provirus form of the RNA virus that causes AIDS15 and for bacterial viruses such as T 7 bacteriophage (39,936 bp).16 Also determined in the 1980s were sequences of human mitochondrial DNA (16,598 bp),17 and of chloroplast DNA from the tobacco plant (155,844 bp).18... 

Ethidium bromide inhibits the replication of chloroplast DNA and causes partial degradation of existing DNA in chloroplasts without interfering with replication of DNA in the nucleus. The effect is similar to that of the same drug on mitochondrial DNA. 

Mitochondrial and Mitochondria and chloroplasts contain their own DNA, ribosomes, mRNA, etc., chloroplast and carry out protein synthesis, but very few mitochondrial or chloroplast... 

The main argument in favour of this hypothesis is the presence in chloroplasts and mitochondria of DNA, which is different from the nuclear DNA and similar to the DNA of prokaryotes, as well as the similarity of chloroplast, mitochondrial and bacterial ribosomes and their significant difference from cytoplasmic ribosomes of eukaryotic cells. The chloroplasts and mitochondria were found to be close to bacterial cells in additional other biochemical features the presence in their membranes of phospholipid cardiolipin, which is absent in the plasma membrane of eukaryotes, and ATPases of one and the same type FiF0. 

Isolation and comparisons of nucleic acids are being carried out on an ever increasing number of plant species. For many of these taxa, the procedures described previously for nuclear DNA,1>2 chloroplast DNA,3 and mitochondrial DNA4-6 have been invaluable. An additional, new source detailing many aspects of nucleic acid comparisons is highly recommended.7 This chapter describes protocols that we have found useful with plants containing many secondary metabolites. In addition, it summarizes procedures from other laboratories that may be helpful in future studies involving nucleic acid comparisons. 

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