Eukaryotes organelles

Plant cells also contain all of these characteristic eukaryotic organelles, essentially in the form described for animal cells. 

ATP-dependent proteases are complex proteolytic machines. They are present in eubacteria, archaebacteria, in eukaryotic organelles and, as the 20S or 26S proteasome, in the eukaryotic cytosol and nucleoplasm. The activators of all known ATP-dependent proteases are related. They all contain an AAA(+) ATPase domain as a module (Neuwald et al. 1999) and are thought to assemble into hexameric particles or, in the case of 26S proteasomes, are present in six variants in the 19S activators (Glickman et al. 1999). Like the ATPases, the proteolytic components of the ATP-dependent proteases form higher order complexes, but unlike for the ATPases, the symmetry of the protease assemblies varies, and the folds of the subunits need not be related. ClpP is a serine protease, FtsH a metalloprotease, and HslV and the proteasomes from archaebacteria and eubacteria are threomne proteases. 

Knoblauch, M. et al. (1999). A galinstan expansion femotosyringe for microinjection of eukaryotic organelles and prokaryotes. Nat. Biotechnol. 17 906-909. 

Protein trafficking has been extensively studied in fungi and mammals, and a number of elaborate machines have been described that specifically import certain proteins into typical eukaryotic organelles such as the nucleus, the endoplasmic reticulum and the mitochondrion. 

Viale AM, Arakaki AK (1994) The chaperone connection to the origins of the eukaryotic organelles. FEBS Lett 341 146-151... 

Fig. 10.2. The phylogenetic distribution of mitochondrion-related organelles in eukaryotes. Organelle function is indicated as Hhydrogenosome, M mitosome or unknown...

Plant/fungal/bacterial peroxidases. Haem-containing peroxidases from plants, fungi and bacteria are structurally related and form a superfamily. All enzymes so far studied have mechanisms of the type illustrated in Fig. 2. They fall into three diverse classes [23,24], Class I are found in prokaryotes and some eukaryotic organelles. The best-characterised of these enzymes... 

Overmann J, van Gemerden H. Microbial interactions involving sulfur bacteria implications for the ecology and evolution of bacterial communities. FEMS Microbiol. Rev. 2000 24 591-599. Margulis L. Symbiotic theory of the origin of eukaryotic organelles criteria for proof. Symp. Soc. Exp. Biol. 1975 29 21-38. Smith DC, Bernays FA. Why do so few animals form endosymbiotic associations with photosynthetic microbes . Phil. Trans. R. Soc. Lond. B 1991 333 225-230. 

Whatever the explanation of the stem eukaryote, the eukaryote organelles, both mitochondria and chloroplasts, are best explained as symbiont bacteria. Explanations of the mitochondrial symbiosis mostly invoke an early Archean stem that incorporated a bacterial symbiont. One explanation of the mitochondrion is that the origin of the mitochondrion was simultaneous with the origin of the eukaryote nucleus (Grey et al, 1999). In the hydrogen hypothesis (Martin and Muller, 1998), the symbiosis is seen as the end product of a tight physical association between anaerobic... 

Golgi apparatus. Eukaryotic organelle that package cell products, such as enzymes and hormones, and coordinate their transport to the outside of the cell. 

Like the plasma membrane, the membrane surrounding each organelle in eukaryotic cells contains a unique set of proteins essential for its proper functioning. In the next section, we provide a brief overview of the main eukaryotic organelles. 

The endoplasmic reticulum is a eukaryotic organelle with many functions. The outer surface of the structure is often coated with ribosomes undergoing protein synthesis. Proteins to be processed in other ways, such as addition of sugars, are synthesized and transported into the endoplasmic reticulum. Many biological reactions on nonpolar lipid molecules occur in the endoplasmic reticulum. 

Michael Knoblauch, Julian M. Hibberd, John C. Gray and Aart J. E. van Bel, A galinstan expansion femtosysringe for micro-injection of eukaryotic organelles and prokaryotes. Nature Biotechnology, 17 (1999), 906-909. 

The nucleus is perhaps the most important eukaryotic organelle. A typical nucleus exhibits several important structural features (Figure 1.12). It is surrounded by a nuclear double membrane (usually called the nuclear envelope). One of its prominent features is the nucleolus, which is rich in RNA. The RNA... 

A second very important eukaryotic organelle is the mitochondrion, which, like the nucleus, has a double membrane (Figure 1.13). The outer membrane has a fairly smooth surface, but the inner membrane exhibits many folds called cristae. The space within the inner membrane is called the matrix. Oxidation processes that occur in mitochondria yield energy for the cell. Most of the enzymes responsible for these important reactions are associated with the inner mitochondrial membrane. Other enzymes needed for oxidation reactions, as well as DNA that differs from that found in the nucleus, are found in the internal mitochondrial matrix. Mitochondria also contain ribosomes similar to those found in bacteria. Mitochondria are approximately the size of many bacteria, typically about 1 pm in diameter and 2 to 8 pm in length. In theory, they may have arisen from the absorption of aerobic bacteria by larger host cells. 

It is unlikely that mitochondria would be found in bacteria. These eukaryotic organelles are enclosed by a double membrane, and bacteria do not have an internal membrane system. The mitochondria found in eukaryotic cells are about the same size as most bacteria. 

Margulis, Lynn (bom 1938) American biologist she is best known for her theory on the origin of eukaryotic organelles, and her contributions to the endosymbiotic theory. 

The eukaryotic DNA is organized in to one or more linear molecules, called chromosomes, which are associated with histone proteins. All chromosomal DNA is stored in the cell nucleus, separated from the cytoplasm by a membrane. Some eukaryotic organelles such as mitochondria also contain some DNA. Many eukaryotic cells are ciliated with primary cilia. Eukaryotes can move using motile cilia or flagella. 

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