Mitochondria of eukaryotic cells

Two nucleic acids, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), are found in living things which serve to store, translate, and pass on the genetic information of an organism to the next generation. Nucleic acids are universal to all life, in eukaryotic and prokaryotic cells, as well as in viruses. The mitochondria of eukaryotic cells also contain some DNA, known as mitochondrial DNA. 

In respiration, substrate organic molecules containing carbon-hydrogen bonds (food) and oxygen are absorbed by prokaryotic cells or by the mitochondria of eukaryotic cells. The oxygen reacts with electrons that are derived from metabolic changes to the carbon-hydrogen bonds of the substrates. The final steps of substrate metabolism, the Krebs cycle,... 

The answer is c. (Murray, pp 452—467. Scriver, pp 3—45. Sack, pp 1—40. Wilson, pp 101-120.) Prokaryotic ribosomes have a sedimentation coefficient of 70S and are composed of SOS and 30S subunits. Eukaryotic cytoplasmic ribosomes, either free or bound to the endoplasmic reticulum, are larger—60S and 40S subunits that associate to an SOS ribosome. Nuclear ribosomes are attached to the endoplasmic reticulum of the nuclear membrane. Ribosomes in chloroplasts and mitochondria of eukaryotic cells are more similar to prokaryotic ribosomes than to eukaryotic cytosolic ribosomes. Like bacterial ribosomes, chloroplast and mitochondrial ribosomes use a formylated tRNA. In addition, they are sensitive to many of the inhibitors of protein synthesis in bacteria. 

These are (1) the copper-zinc superoxide dismutases, CuZnSOD, °° ° found in almost all eukaryotic cells and a very few prokaryotes, and (2) the manganese and iron superoxide dismutases, MnSOD and FeSOD, the former found in the mitochondria of eukaryotic cells, and both found in many prokaryotes. Recent studies of bacterial and yeast mutants that were engineered to contain no superoxide dismutases demonstrated that the cells were unusually sensitive... 

The mitochondria of eukaryotic cells have many features in common with prokaryotic cells and, in fact, may have originated when primordial anaerobic eukaryotes engulfed ancient aerobic prokaryotes, establishing a symbiotic relationship. These prokaryotes provided eukaryotes with a more efficient mechanism for oxidizing fuels to obtain energy. 

Ribosomes are subcellular ribonucleoprotein complexes on which protein synthesis occurs. Different types of ribosomes are found in prokaryotes and in the cytoplasm and mitochondria of eukaryotic cells (Fig. 12.20). Prokaryotic ribosomes contain three types of rRNA molecules with sedimentation coefficients of 16, 23, and 5S. The 30S ribosomal subunit contains the 16S rRNA complexed with proteins, and... 

In cell-free systems the inhibition of the transfer of aminoacyl-transfer RNAs to polypeptide (at the ribosome level) is probably the primary effect The most interesting effect of cycloheximide is that protein synthesis by isolated mitochondria of eukaryotic cells, like bacterial ribosomes, but unlike mammalian and yeast cytoplasmic ribosomes, is not inhibited over a wide range of concentrations. Despite this selective action, cycloheximide is extremely harmful to the biogenesis of mitochondria in vivo, due to a large contribution of the microsomal protein synthesizing system in the formation of mitochondrial proteins. 

Mitochondria Mitochondria are organelles surrounded by two membranes that differ markedly in their protein and lipid composition. The inner membrane and its interior volume, the matrix, contain many important enzymes of energy metabolism. Mitochondria are about the size of bacteria, 1 fim. Cells contain hundreds of mitochondria, which collectively occupy about one-fifth of the cell volume. Mitochondria are the power plants of eukaryotic cells where carbohydrates, fats, and amino acids are oxidized to CO9 and H9O. The energy released is trapped as high-energy phosphate bonds in ATR... 

IV. Superoxide dismutase (EC 1.15.1.1) Within a cell the superoxide dismutases (SODs) constitute the first line of defense against ROS. Superoxide radical (02) is produced where an electron transport chain is present, as in mitochondria and chloroplasts, but 02 activation may occur in other subcellular locations such as glyoxysomes, peroxisomes, apoplast and the cytosol. Thus SODs are present in all these cellular locations, converting superoxide into hydrogen peroxide and water (i.e. copper/zinc SODs are typically found in the nuclei and cytosol of eukaryotic cells). 

The radical anion superoxide 02 is a product of activated leukocytes and endothelial cells and has been postulated to be a mediator of isch-emia-reperfusion injury and inflammatory and vascular diseases. Various superoxide dismutase (SOD) enzymes are known Cu,Zn-SOD in the cytoplasm of eukaryotic cells, Mn-SOD in mitochondria, and Fe-SOD and Mn-SOD in prokaryotic cells. They catalyze the conversion of 02 into H202 and 02... 

According to one favored theory, mitochondria evolved from aerobic bacteria that were endocytosed by an anaerobic ancestor of eukaryotic cells. The endocytic event is thought to have occurred when oxygen emerged in the atmosphere (about two billion years ago) and threatened most life systems. Under the selective pressure of oxygen, a stable relationship developed in which the host cell had acquired the ability to exploit the bacterial oxidative phosphorylation system for their own use (Green and... 

Eukaryotic cells alone possess enclosed subcellular structures, including, for example, the mitochondria. Mitochondria are the powerhouses of eukaryotic cells and 1 will have much more to say about them in chapter 17. For the present, it has been recognized for some years that the mitochondria are derived from bacteria at some point in the distant past. The basic idea is that an earlier eukaryotic cell captured a bacterium at some point and symbiotic relationships developed. The story may be more complex and more interesting. 

The (Cu,Zn)-SOD is found in the cytosol of eukaryotic cells and in the intermembrane space of mitochondria, as observed with chicken liver and also in chloroplasts, as shown with spinach and mustard leaves. A (Cu,Zn)-SOD has also been isolated from a prokaryote Photobacterium leiognathi. Could this symbiotic bacterium have borrowed the gene(s) from its host, the Pony fish, although two different subunits (Af 15,000 and 17,000) were reported for the bacterial enzyme A (Cu,Zn)-SOD was furthermore detected in Paracoccus denitrificans... 

Bui ET, Bradley PJ, Johnson PJ (1996) A common evolutionary origin for mitochondria and hydrogenosomes. Proc Natl Acad Sci USA 93 9651-9695 Cavalier-Smith T (1975) The origin of nuclei and of eukaryotic cells. Nature 256 463-468 Cavalier-Smith T (1983) Endosymbiotic origin of the mitochondrial envelope. In Schwemmler W, Schenk HEA (eds) Endocytobiology II. Intracellular space as an oligogenetic ecosystem. De Gutyer, Berlin, pp 265-279... 

Margulis L (2005) Origin of eukaryotic cells. Yale University Press, New Haven Martin W (2000) Primitive anaerobic protozoa the wrong host for mitochondria and hydrogenosomes Microbiology 146 1021-1022... 

The origin of eukaryotic cells and particularly mitochondria is an old but still hotly debated topic. The endosymbiotic model proposed the... 

Circular DNA is present in prokaryotes and in the mitochondria of eukaryotes. Collagen, a fibrous protein, and proteoglycans constitute the matrix in which cells are located. 

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. 

Globally speaking, photosynthesis takes place in the chloroplast and respiration takes place in the mitochondrion. Both chloroplasts and mitochondria are organelles of eukaryotic cells. They look in many respects like cells within the cell and... 

In addition to a distinction based on microhabitats, variation in symbiont-host relationships gives rise to different terminology. In a mutualism, both the host and the symbiont profit from their relationship. Mutualism, therefore, is defined as the cooperative interaction between different species. Virtually every higher organism is involved in mumal interactions because mitochondria and chloroplasts of eukaryotic cells are descendants of bacteria (see below). Other examples are plants associated... 

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