Eukaryotic cell systems

Although the compounds were isolated in quantities of only a few milligrams per kilogram of cmde plant leaves, extensive work on a variety of animal tumor systems led to eventual clinical use of these bases, first alone and later in conjunction with other materials, in the treatment of Hodgkin s disease and acute lymphoblastic leukemia. Their main effect appears to be binding tightly to tubuHn, the basic component of microtubules found in eukaryotic cells, thus interfering with its polymerization and hence the formation of microtubules required for tumor proliferation (82). 

Without consulting chapter figures, sketch the characteristic prokaryotic and eukaryotic cell types and label their pertinent organelle and membrane systems. 

The processes of electron transport and oxidative phosphorylation are membrane-associated. Bacteria are the simplest life form, and bacterial cells typically consist of a single cellular compartment surrounded by a plasma membrane and a more rigid cell wall. In such a system, the conversion of energy from NADH and [FADHg] to the energy of ATP via electron transport and oxidative phosphorylation is carried out at (and across) the plasma membrane. In eukaryotic cells, electron transport and oxidative phosphorylation are localized in mitochondria, which are also the sites of TCA cycle activity and (as we shall see in Chapter 24) fatty acid oxidation. Mammalian cells contain from 800 to 2500 mitochondria other types of cells may have as few as one or two or as many as half a million mitochondria. Human erythrocytes, whose purpose is simply to transport oxygen to tissues, contain no mitochondria at all. The typical mitochondrion is about 0.5 0.3 microns in diameter and from 0.5 micron to several microns long its overall shape is sensitive to metabolic conditions in the cell. 

Most of the NADH used in electron transport is produced in the mitochondrial matrix space, an appropriate site because NADH is oxidized by Complex I on the matrix side of the inner membrane. Furthermore, the inner mitochondrial membrane is impermeable to NADH. Recall, however, that NADH is produced in glycolysis by glyceraldehyde-3-P dehydrogenase in the cytosol. If this NADH were not oxidized to regenerate NAD, the glycolytic pathway would cease to function due to NAD limitation. Eukaryotic cells have a number of shuttle systems that harvest the electrons of cytosolic NADH for delivery to mitochondria without actually transporting NADH across the inner membrane (Figures 21.33 and 21.34). 

Heterologous expression systems comprise prokaryotic organisms (e.g., E. coli) and eukaryotic cells (e.g., yeast, HEK293, Xenopus oocytes), which are used to functionally express foreign genes or cDNAs. 

Host system Prokaryotes Eukaryotes Cell- free systems... 

Additional studies were performed with eukaryotic cell systems (i.e. Chinese hamster ovary cells, rat bone mar-... 

Here, we discuss a solid-state 19F-NMR approach that has been developed for structural studies of MAPs in lipid bilayers, and how this can be translated to measurements in native biomembranes. We review the essentials of the methodology and discuss key objectives in the practice of 19F-labelling of peptides. Furthermore, the preparation of macroscopically oriented biomembranes on solid supports is discussed in the context of other membrane models. Two native biomembrane systems are presented as examples human erythrocyte ghosts as representatives of eukaryotic cell membranes, and protoplasts from Micrococcus luteus as membranes... 

GFP has also been proposed as a successor to the Ames and SOS chromotest. Billinton et al. [8] obtained a reporter system, employed as genotoxicity biosensor, that uses eukaryotic cells (the baker yeast Saccharomyces cerevisiae) instead of bacteria. The strain produces green fluorescent protein, codon optimized for yeast, when DNA damage has occurred. It was demonstrated that the reporter does not falsely respond to chemicals that delay mitosis, and responds appropriately to the genetic regulation of DNA repair. 

Eukaryotic cells have evolved a complex, intracellular membrane organization. This organization is partially achieved by compartmentalization of cellular processes within specialized membrane-bounded organelles. Each organelle has a unique protein and lipid composition. This internal membrane system allows cells to perform two essential functions to sort and deliver fully processed membrane proteins, lipids and carbohydrates to specific intracellular compartments, the plasma membrane and the cell exterior, and to uptake macromolecules from the cell exterior (reviewed in [1,2]). Both processes are highly developed in cells of the nervous system, playing critical roles in the function and even survival of neurons and glia. 

Eukaryotic cells utilize an efficient transport system that delivers macromolecules fast and secure to their destination. In the case of the small GTP binding proteins of the Ras family the modified C-terminus seems to be sufficient for addressing the polypeptide to its target membrane (in the case of Ras itself the plasma membrane). Lipopeptides with the C-terminal structure of N-Ras (either a pen-tamer with a C-terminal carboxymethylation and farnesylation or a heptapeptide with a palmitoyl thioester in addition) and a N-terminal 7-nitrobenz-2-oxa-l,3-diazolyl (NBD) fluorophore were microin-jected into NIH3T3 fibroblast cells and the distribution of the fluorophore was monitored by confocal laser fluorescence microscopy. Enrichment of the protein in the plasma membrane was efficient only for peptides with two hydrophobic modification sites, while the farnesylated but not palmitoylated peptide was distributed in the cytosol.1121... 

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