Mitochondrion and nucleus

Williams and Keeling 2002). We also suggest that this close association of the mitochondrion-like organelle and endomembrane system facilitates the assembly of cytosolic Rlil, the only known essential FeS protein for yeast viability (Iill et al. 2005 reviewed in Tachezy and Dolezal 2007). These data are consistent with previous hypotheses that the primary function of the mitochondrion-like organelle in C. parvum is the assembly of FeS clusters in order to provide mature FeS proteins to all cellular compartments, including the cytosol, mitochondrion, and nucleus. 

Although cross-talk between the mitochondrion and nucleus occius in all eukaryotes it is best understood in S. cerevisiae (56). In this organism, the mitochondrion can... 

Directly beneath the ceU wall is a membrane called the cytoplasmic membrane that surrounds the cytoplasm. In the eucaryotes, an organelle caUed mitochondrion, and, in the photosynthetic eucaryotes, an organeUe caUed chloroplast are the sites for the electron-tranport and the respiratory enzyme systems. The bacteria do not have the mitochondrion nor the chloroplast, but the functions of these organelles are embedded within the sites in the cytoplasmic membrane. The cytoplasm is the Uving material which the cell is composed of, minus the nucleus. 

Most proteins are synthesi2ed on ribosomes that float freely in the cytoplasm. After synthesis of the polypeptide chain, the completed protein dissociates from the ribosome and begins to function. Some of the proteins of the cytosol contain special sequences (or clusters) of amino acids that guide the entire protein into the mitochondrion or nucleus to perform functions specific to that organelle- Many other proteins are synthesized on ribosomes that are bound to the endoplasmic... 

Figure 4. Scheme showing sperm-egg interaction in the abalone. 1. The sperm binds to the egg VE by the plasma membrane at the tip of the AV (AG), (F, flagellum M, mitochondrion N, nucleus). 2. The sperm acrosome reacts releasing lysin and the 18K protein from its anterior tip. 3. Lysin disrupts the fibers of the VE and the 18K coats the extending acrosome process as it extends. 4. The sperm passes through the hole in the VE and the membrane covering the tip of the acrosomal process fuses with the egg (from Vacquier and Lee, 1993). 

The nucleus, mitochondrion, and chloroplast are bounded by two bIlayer membranes separated by an intermembrane space. All other organelles are surrounded by a single membrane. 

Three of the most important organelles in eukaryotic cells are the nucleus, the mitochondrion, and the chloroplast. Each is separated from the rest of the cell by a double membrane. The nucleus contains most of the DNA of the cell... 

Thin section of a Rhodosorus cell, showing the chloroplast and other organelles. Various views of the phycobilisomes can be seen due to the angles at which different thylakoids have been sectioned. Plug-like structures are visible in the inset (circle), c = chloroplast m = mitochondrion n = nucleus p = pyrenoid s= starch grain. 

Fig. 2.6 The moqjhological events of sporulation in Saccharomyces cerevisiae. (a) starved cell V, vacuole LG, lipid granule ER, endoplasmic reticulum CW, cell wall M, mitochondrion S, spindle pole SM, spindle microtubules N, nucleus NO, nucleolus, (b) Synaptonemal complex (SX) and development of polycomplex body (PB) along with division of spindle pole body in (c). (d) First meiotic division which is completed in (e). (f) Prepararation for meiosis II. (g) Enlargement of prospore wall, culminating in enclosure of separate haploid nuclei (h). (i) Spore coat (SC) materials produced and deposited, giving rise to the distinct outer spore coat (OSC) seen in the completed spores of the mature ascus (j). Reproduced from the review by Dickinson (1988) with permission from Blackwell Science Ltd.

Not all the cellular DNA is in the nucleus some is found in the mitochondria. In addition, mitochondria contain RNA as well as several enzymes used for protein synthesis. Interestingly, mitochond-rial RNA and DNA bear a closer resemblance to the nucleic acid of bacterial cells than they do to animal cells. For example, the rather small DNA molecule of the mitochondrion is circular and does not form nucleosomes. Its information is contained in approximately 16,500 nucleotides that func-tion in the synthesis of two ribosomal and 22 transfer RNAs (tRNAs). In addition, mitochondrial DNA codes for the synthesis of 13 proteins, all components of the respiratory chain and the oxidative phosphorylation system. Still, mitochondrial DNA does not contain sufficient information for the synthesis of all mitochondrial proteins most are coded by nuclear genes. Most mitochondrial proteins are synthesized in the cytosol from nuclear-derived messenger RNAs (mRNAs) and then transported into the mito-chondria, where they contribute to both the structural and the functional elements of this organelle. Because mitochondria are inherited cytoplasmically, an individual does not necessarily receive mitochondrial nucleic acid equally from each parent. In fact, mito-chondria are inherited maternally. 

In spite of the variety of appearances of eukaryotic cells, their intracellular structures are essentially the same. Because of their extensive internal membrane structure, however, the problem of precise protein sorting for eukaryotic cells becomes much more difficult than that for bacteria. Figure 4 schematically illustrates this situation. There are various membrane-bound compartments within the cell. Such compartments are called organelles. Besides the plasma membrane, a typical animal cell has the nucleus, the mitochondrion (which has two membranes see Fig. 6), the peroxisome, the ER, the Golgi apparatus, the lysosome, and the endosome, among others. As for the Golgi apparatus, there are more precise distinctions between the cis, medial, and trans cisternae, and the TGN trans Golgi network) (see Fig. 8). In typical plant cells, the chloroplast (which has three membranes see Fig. 7) and the cell wall are added, and the lysosome is replaced with the vacuole. 

Figure 11.1 Ultrastructure of the human lung alveolar barrier. The tissue specimen is obtained via lung resection surgery. (A) Section through a septal wall of an alveolus. The wall is lined by a thin cellular layer formed by alveolar epithelial type I cells (ATI). Connective tissues (ct) separate ATI cells from the capillary endothelium (en) within which an erythrocyte (er) and granulocyte (gc) can be seen. The minimal distance between the alveolar airspace (ai) and erythrocyte is about 800-900 nm. The endothelial nucleus is denoted as n. (B) Details of the lung alveolar epithelial and endothelial barriers. Numerous caveolae (arrows) are seen in the apical and basal plasma membranes of an ATI cell as well as endothelial cell (en) membranes. Caveolae may partake transport of some solutes (e.g., albumin). (C) ATII cells (ATII) are often localised in the comers of alveoli where septal walls branch off. (D) ATII cells are characterised by numerous multilamellar bodies (mlb) which contain components of surfactant. A mitochondrion is denoted as mi.

The cell organellae in woody plants are the nucleus, mitochondrion, rough-endoplasmic reticulum (r-ER), smooth endoplasmic reticulum (s-ER), Golgi-body, plastid, vacuole, microbody, etc. Their functions are very complicated, and some have definite roles in the biosynthesis of cell-wall components. Hence, changes in size of cell organellae are likely to occur, since cell-wall composition depends upon the stage of wall development. 

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. 

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