Membranes, cell Plasma membrane

Prokaryotic cells have only a single membrane, the plasma membrane or cell membrane. Because they have no other membranes, prokaryotic cells contain no nucleus or organelles. Nevertheless, they possess a distinct nuclear area where a single circular chromosome is localized, and some have an internal membranous structure called a mesosome that is derived from and continuous with the cell membrane. Reactions of cellular respiration are localized on these membranes. In photosynthetic prokaryotes such as the cyanobacteria,... 

Cholesterol is a principal component of animal cell plasma membranes, and much smaller amounts of cholesterol are found in the membranes of intracellular organelles. The relatively rigid fused ring system of cholesterol and the weakly polar alcohol group at the C-3 position have important consequences for the properties of plasma membranes. Cholesterol is also a component of lipoprotein complexes in the blood, and it is one of the constituents oiplaques that form on arterial walls in atherosclerosis. 

Cells make use of many different types of membranes. All cells have a cytoplasmic membrane, or plasma membrane, that functions (in part) to separate the cytoplasm from the surroundings. In the early days of biochemistry, the plasma membrane was not accorded many functions other than this one of partition. We now know that the plasma membrane is also responsible for (1) the exclusion of certain toxic ions and molecules from the cell, (2) the accumulation of cell nutrients, and (3) energy transduction. It functions in (4) cell locomotion, (5) reproduction, (6) signal transduction processes, and (7) interactions with molecules or other cells in the vicinity. 

Cholesterol is a widely distributed sterol found free or esterified to fatty acids. It is an important intermediate in the biosynthesis of steroid hormones and the principal component of cell plasma membranes and the membranes of intracellular organelles. 

Thus far, microtubules and actin filaments and their associated proteins have been discussed to advantage as independent cytoskeletal components. In actual fact, all of the components of the cytoskeleton (including intermediate filaments) are precisely integrated with one another (Langford, 1995), as well as with various cytoplasmic organelles, the nuclear membrane, the plasma membrane, and the extracellular matrix. In its totality the cytoskeleton subserves many coordinated and regulated functions in the cell ... 

It has been proposed " that the mechanism(s) of action of gymnemic acids and ziziphins is a biphasic, model-membrane penetration-process. The model suggested that the modifier molecules interact first with the receptor-cell plasma-membrane surface. It was postulated that this initial interaction involves a selective effect on taste perception, including the transduction and quality specification of the sweet stimuli, and selective depression of sweetness perception. Following the initial interaction, the modifier molecules interact with the membrane-lipid interior to produce a general disruption of membrane function and a nonselective effect on taste... 

Shynkar VV, Klymchenko AS, Duportial G et al (2005) Two-colour fluorescent probes for imaging the dipole potential of cell plasma membranes. Biochim Biophys Acta Biomem 1712 128-136... 

McNeil, P.L. and Ito, S. (1989) Gastrointestinal cell plasma membrane wounding and resealing in vivo. Gastroenterology 96, 1238-1248. 

Figure 12.2 Copper chaperone function, (a) Copper homeostasis in Enterococcus hirae is affected by the proteins encoded by the cop operon. CopA, Cu1+-import ATPase CopB, Cu1+-export ATPase CopY, Cu1+-responsive repressor copZ, chaperone for Cu1+ delivery to CopY. (b) The CTR family of proteins transports copper into yeast cells. Atxlp delivers copper to the CPx-type ATPases located in the post Golgi apparatus for the maturation of Fet3p. (c) Coxl7p delivers copper to the mitochondrial intermembrane space for incorporation into cytochrome c oxidase (CCO). (d) hCTR, a human homologue of CTR, mediates copper-ion uptake into human cells. CCS delivers copper to cytoplasmic Cu/Zn superoxide dismutase (SOD1). Abbreviations IMM, inner mitochondrial membrane OMM, outer mitochondrial membrane PM, plasma membrane PGV, post Golgi vessel. Reprinted from Harrison et al., 2000. Copyright (2000), with permission from Elsevier Science.

Kenworthy, A. K., Petranova, N. and Edidin, M. (2000). High resolution FRET microscopy of cholera toxin B-subunit and GPI-anchored proteins in cell plasma membranes. Mol. Biol. Cell 11, 1645-55. 

To reach the reductive step of the azo bond cleavage, due to the reaction between reduced electron carriers (flavins or hydroquinones) and azo dyes, either the reduced electron carrier or the azo compound should pass the cell plasma membrane barrier. Highly polar azo dyes, such as sulfonated compounds, cannot pass the plasma membrane barrier, as sulfonic acid substitution of the azo dye structure apparently blocks effective dye permeation [28], The removal of the block to the dye permeation by treatment with toluene of Bacillus cereus cells induced a significant increase of the uptake of sulfonated azo dyes and of their reduction rate [29]. Moreover, cell extracts usually show to be more active in anaerobic reduction of azo dyes than whole cells. Therefore, intracellular reductases activities are not the best way to reach sulfonated azo dyes reduction the biological systems in which the transport of redox mediators or of azo dye through the plasma membrane is not required are preferable to achieve their degradation [13]. 

The biosynthetic, secretory pathway is responsible for protein sorting and delivery and allows, among other functions, for cell-cell communication through secreted products. This delivery process starts at the endoplasmic reticulum (ER), to finish in the cell plasma membrane or, in some cases, in specific intracellular organelles. To accomplish this, specific proteins must be properly directed to the correct destination, while other proteins are retained as residents within specific organelles along the way. 

Vickers, S., Schiller, H. J., Hildreth, J. E., Bulkley, G. B., Immunoaffmity localization of the enzyme xanthine oxidase on the outside surface of endothelial cell plasma membrane. Surgery 124 (1998), p. 551-560... 

An anomaly associated with citrulline that became evident when detailed kinetic studies were made in the 1950s (R.B. Fisher and J.R. Bronk) was the irreproducibility of its catalytic activity in liver slices on the formation of urea, despite the clear evidence from Ratner and Petrack of its importance in arginine synthesis. Initially the discrepancy in catalytic activity between ornithine and citrulline was ascribed to the possible impermeability of the liver cell plasma membrane to the latter intermediate, a hypothesis which was rapidly disproved experimentally. Only recently has it been shown that ornithine transcarbamylase is clearly associated with the ornithine/... 

Most of the early work on membranes was based on experiments with erythrocytes. These cells were first described by Swammerdam in 1658 with a more detailed account being given by van Leeuwenhoek (1673). The existence of a cell (plasma) membrane with properties distinct from those of protoplasm followed from the work of Hamburger (1898) who showed that when placed in an isotonic solution of sodium chloride, erythrocytes behaved as osmometers with a semipermeable membrane. Hemolysis became a convenient indication of the penetration of solutes and water into the cell. From 1900 until the early 1960s studies on cell membranes fell into two main categories increasingly sophisticated kinetic analyses of solute translocation, and rather less satisfactory examinations of membrane composition and organization. 

The cell plasma membrane separates the cell cytoplasm from the external medium. The composition of the cytoplasm must be tightly controlled to optimize cellular processes, but the composition of the external medium is highly variable. The membrane is hydrophobic and impedes solute diffusion. But it also facilitates and regulates solute transfers as the cell absorbs nutrients, expels wastes and maintains turgour. 

Zhang, P., Johnson, P. S., Zollner, C., et al. (1999) Mutation of human mu opioid receptor extracellular disulfide cysteine residues alters hgand binding but does not prevent receptor targeting to the cell plasma membrane. Brain Res. Mol. Brain Res. 72, 195-204. 

Injury to cell plasma membrane can activate acid sphingomyelinase to break down membrane lipid sphingomyelin and generate the second messenger ceramide, a complex lipid, to initiate the apoptosis (HI). Ceramide, perhaps through intracellular mitogen-activated protein kinases (MAPK), can alter cellular susceptibility to TNF-a, FasL, and ionizing radiation-induced apoptosis (HI, Wll). 

Osmosis, water movement across a semipermeable membrane driven by differences in osmotic pressure, is an important factor in the life of most cells. Plasma membranes are more permeable to water than to most other small molecules, ions, and macromolecules. This permeability is due partly to simple diffusion of water through the lipid bilayer and partly to protein channels (aquaporins see Fig. 11-XX) in the membrane that selectively permit the passage of water. Solutions of equal osmolarity are said to be isotonic. Surrounded by an isotonic solution, a cell neither gains nor loses water (Fig. 2-13). In a hypertonic solution, one with higher... 

Chemical analyses of membranes isolated from various sources reveal certain common properties. Each kingdom, each species, each tissue or cell type, and the organelles of each cell type have a characteristic set of membrane lipids. Plasma membranes, for example, are enriched in cholesterol and contain no detectable cardiolipin (Fig. 11-2) in the inner mitochondrial membrane of the hepatocyte, this distribution is reversed very low cholesterol and high cardiolipin. Cardiolipin is essential to the function of certain proteins of the inner mitochondrial membrane. Cells clearly have mechanisms to control the kinds and amounts of membrane lipids they synthesize and to target specific lipids to particular organelles. In many cases, we can surmise the adaptive advantages of distinct combinations of membrane lipids in other cases, the functional significance of these combinations is as yet unknown. 

Eukaryotic cell plasma membranes Muscle sarcoplasmic reticulum Eukaryotic cell plasma membranes Stomach epithelial cell plasma membranes... 

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