Mitochondria functional

The law of the minimum is easy to understand on a cellular, molecular, and atomic level and is applicable to all organisms. Organisms cannot grow by producing partial cells and to produce a whole cell they must have all the constituents in the correct proportion, ft is not possible to have a functioning cell that does not have a complete cell membrane, complete genetic material, functional mitochondria, and all the other parts of a functioning cell. 

Mitochondria are distinct organelles with two membranes. The outer membrane limits the organelle and the inner membrane is thrown into folds or shelves that project inward and are called cristae mitochondriales. The uptake of most mitochondrion-selective dyes is dependent on the mitochondrial membrane potential. Conventional fluorescent stains for mitochondria, such as rhodamine and tetramethylrosamine, are readily sequestered by functioning mitochondria. They are, however, subsequently washed out of the cells once the mitochondrion s membrane potential is lost. This characteristic limits their use in experiments in which cells must be treated with aldehyde-based fixatives or other agents that affect the energetic state of the mitochondria. To overcome this limitation, the research... 

Consequently, repeated exposure to nucleoside analogues such as fialuridine leads to impaired function of the cell because of the reduced number of functioning mitochondria. 

Topical eukaryotic cells (Fig. 1-7) are much larger than prokaryotic cells—commonly 5 to 100 pm in diameter, with cell volumes a thousand to a million times larger than those of bacteria. The distinguishing characteristics of eukaryotes are the nucleus and a variety of membrane-bounded organelles with specific functions mitochondria, endoplasmic reticulum, Golgi complexes, and lysosomes. Plant cells also contain vacuoles and chloroplasts (Fig. 1-7). Also present in the cytoplasm of many cells are granules or droplets containing stored nutrients such as starch and fat. 

Mitochondria evolved by an endosymbiotic event between an anaerobically functioning archaebacterial host and an aerobic a-pro-teobacterium. However, true anaerobically functioning mitochondria, such as those found... 

Next to fumarate reduction, some organisms use specific reactions in lipid biosynthesis as an electron sink to maintain redox balance in anaerobically functioning mitochondria. In anaerobic mitochondria two variants are known the production of branched-chain fatty acids and the production of wax esters. The parasitic nematode Ascaris suum reduces fumarate in its anaerobic mitochondria, but instead of only producing acetate and succinate or propionate, like most other parasitic helminths, this organism also use the intermediates acetyl-CoA and propionyl-CoA to form branched-chain fatty acids (Komuniecki et al. 1989). This pathway is similar to reversal of P-oxidation and a complex mixture of the end products acetate, propionate, succinate and branched-chain fatty acids is excreted. In this pathway, the... 

Fig. 5.3. The major components involved in mitochondrial NADH oxidation in facultative anaerobic mitochondria. In anaerobically functioning mitochondria, NADH is oxidized either by soluble enzymes (left) or by membrane-bound complexes of the electron-transport chain (middle). Under aerobic conditions, a classic respiratory chain is used to oxidize NADH (right). Proton translocation is indicated by H with arrows. Ovals represent the electron transporters RQ, UQ and cytochrome c (cyt. c), and electron transport is indicated by dashed arrows. The vertical bar represents a scale for the standard redox potentials in millivolts. Fum fumarate, NADH-DH NADH dehydrogenase, NADH-ECR soluble NADH enoyl-CoA reductase, RQH2 rhodoquinol, Succ succinate, UQH2 ubiquinol...

Most anaerobically functioning mitochondria use endogenously produced fumarate as a terminal electron-acceptor (see before) and thus contain a FRD as the final respiratory chain complex (Behm 1991). The reduction of fumarate is the reversal of succinate oxidation, a Krebs cycle reaction catalysed by succinate dehydrogenase (SDH), also known as complex II of the electron-transport chain (Fig. 5.3). The interconversion of succinate and fumarate is readily reversible by FRD and SDH complexes in vitro. However, under standard conditions in the cell, oxidation and reduction reactions preferentially occur when electrons are transferred to an acceptor with a higher standard redox potential therefore, electrons derived from the oxidation of succinate to fumarate (E° = + 30 mV) are transferred by SDH to ubiquinone,... 

Fumarate reduction is the most commonly used electron-sink for the reoxidation of reduced cofactors in anaerobically functioning mitochondria (see before). Fumarate reduction is catalysed in these mitochondria by a FRD complex, which is structurally very similar to the SDH complexes present in... 

Anaerobic metabolism is usually considered to be an old and rather primitive way of life, but the scenario described here would imply that anaerobically functioning mitochondria are an adaptation of the traditional type of mitochondria to anaerobic environments hence, these anaerobic mitochondria are in fact a further evolution of aerobic mitochondria. 

Fig. 7.4 (a) Dose-response of the lamellarin M-induced mitochondrial depolarization in P388 cells, (b) Monitoring of the mitochondrial membrane potential (A rm) by realtime flow cytometry, using functional mitochondria isolated from P388 cells and the fluorescent probe JC-1. 

S. cerevisiae is one of the few eukaryotes that can live without functional mitochondria. On the other hand, Sch. pombe requires functional mitochondria for survival as do the higher eukaryotes. 

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