Cristae, mitochondrial

Figure 12-1. Structure of the mitochondrial membranes. Note that the inner membrane contains many folds, or cristae.

The electrophysiological and neuropathological changes are similar to the axonal neuropathy and prominent loss of unmyelinated fibers seen in DSP (Simpson and Tagliati 1995). Although the specific pathological mechanisms of ATN are not fully known, there is abundant indirect evidence of mitochondrial dysfunction as a principal mechanism. Prominent mitochondrial disruption and cristae abnormalities... 

Mitochondria (45-56) are organelles possessing a double membrane, the inner of which is invaginated as cristae. An intermembrane space exists between the inner and outer membranes. The inner membrane consists of an unusually high amount of protein and possesses spherically shaped particles approx 9 nm in diameter. These particles appear to be equivalent to F0, Fb and adenosine triphosphatase. In contrast to the inner membrane, the outer membrane is smooth and appears to be connected to the smooth er. This membrane is permeable to all molecules of 10,000 Dalton or less. A mitochondrial matrix is enclosed by the inner membrane and consists of a ground substance of particles, nucleoids, ribosomes, and electron-transparent regions containing DNA. 

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... 

Studies were also made of mitochondrial physiology. Laird noted that mitochondrial numbers were greater in metabolically active cells like liver (ca. 1000) compared with resting cells like small lymphocytes (<10). Keith Porter linked the extent of cristal surface with the amount of work done by the cell. Muscle mitochondria had significantly more cristae than those from liver. 

As further tissues were examined it became evident that the details of mitochondrial morphology were very variable. While most cells had rod-or sausage-shaped organelles, some were spherical. Other cells had mitochondria with spiral cristae or with massive crystalline inclusions. In confirmation of earlier suggestions from classical microscopists the position of mitochondria in cells was also seen to be linked with the site in the cell where energy was required. In skeletal muscle the mitochondria were adjacent to the myofibrils in the renal tubules they were close to the inner (non-luminal) surface of the cell which was then found to be the location of the Na/K-ATPase involved in active... 

Figure 1.6 Nyctotherus ovalis (an anaerobic heterotrichous ciliate from the hindgut of an American Cockroach) hydrogenosome with mitochondrial-type cristae (white arrows) r putative ribosomes m membrane me methanogenic endosymbiont (methanogenic bacterium) (J.H.P. Hackstein, Catholic University of Nijmegen,The Netherlands).

Mitochondria are bacteria-sized organelles (about 1 X 2 im in size), which are found in large numbers in almost all eukaryotic cells. Typically, there are about 2000 mitochondria per cell, representing around 25% of the cell volume. Mitochondria are enclosed by two membranes—a smooth outer membrane and a markedly folded or tubular inner mitochondrial membrane, which has a large surface and encloses the matrix space. The folds of the inner membrane are known as cristae, and tube-like protrusions are called tubules. The intermembrane space is located between the inner and the outer membranes. 

The infoldings of the mitochondrial IM also differ from those of most Apicomplexa, in which the type and number of cristae vary considerably during the life cycle, ranging from tubular in T. gondii tachyzoites (Melo et al. 

Nasirudeen AM, Tan KS (2004) Isolation and characterization of the mitochondrion-like organelle from Blastocystis hominis.J Microbiol Methods 58 101-109 Painter HJ, Morrisey JM, Mather MW, Vaidya AB (2007) Specific role of mitochondrial electron transport in blood-stage Plasmodium falciparum. Nature 446 88-91 Perkins GA, Song JY, Tarsa L, Deerinck TJ, Ellisman MH, Frey TG (1998) Electron tomography of mitochondria from brown adipocytes reveals crista junctions. J Bioeneerg Biomembr 30 431-432... 

FIGURE 19-1 Biochemical anatomy of a mitochondrion. The convolutions (cristae) of the inner membrane provide a very large surface area. The inner membrane of a single liver mitochondrion may have more than 10,000 sets of electron-transfer systems (respiratory chains) and ATP synthase molecules, distributed over the membrane surface. Heart mitochondria, which have more profuse cristae and thus a much larger area of inner membrane, contain more than three times as many sets of electron-transfer systems as liver mitochondria. The mitochondrial pool of coenzymes and intermediates is functionally separate from the cytosolic pool. The mitochondria of invertebrates, plants, and microbial eukaryotes are similar to those shown here, but with much variation in size, shape, and degree of convolution of the inner membrane. 

However, they do transport electrons and react with 02. Other electron transport particles have been prepared by sonic oscillation. Under the electron microscope such particles appear to be small membranous vesicles resembling mitochondrial cristae. 

Algae are members of the plant kingdom and contain chloroplasts similar to those of higher plants, but prokaryotic photosynthetic organisms do not have chloroplasts. In prokaryotes, the photochemical reactions occur in the plasma membrane, which has extensive invaginations resembling the cristae of the mitochondrial inner membrane (fig. 15.3). Table 15.1 summarizes the main distinctions between the various types of photosynthetic organisms. 

Scorrano, L., Ashiya, M., Buttle, K., Weiler, S., Oakes, S. A., Mannella, C. A., and Korsmeyer, S. J., 2002, A distinct pathway remodels mitochondrial cristae and mobilizes cytochrome c during apoptosis, Dev. Cell 2, pp. 55-67... 

The results of studies using a wide range of oxidizable substrates showed that, in fact, there was a modicum of temperature compensation, but that it was nothing like the metabolic cold adaptation originally envisaged. Some thermal compensation was also achieved by increasing the density of cristae within the mitochondria, but this was of less importance than actual mitochondrial density. 

The more secure new rooting of the eukaryotic tree (Fig. 8.1) is between bikonts, which almost certainly ancestrally had tubular mitochondrial cristae, and unikonts, which comprise the Amoebozoa with tubular cristae and opisthokonts with flat cristae (Richards and Cavalier-Smith 2005 Stechmann and Cavalier Smith 2003). The cenancestral eukaryote probably therefore had tubular mitochondrial cristae. The majority of photosynthetic a-proteobacteria have tubular chromatophores, which carry the dual... 

---