Cellular compartments

The primary use of EIA when it was first developed was for histological labeling and localization of specific cell macromolecules. Eor example, enzymes labeled with peroxidase were used to locate specific cellular compartments and stmctures for microscopic examination. The flexibiUty of EIA was recognized quickly and it was adapted for use as a laboratory assay. 

An effective therapeutic agent must also have the abiUty to reach its target sequence m vivo. BioavailabiUty requires that the antisense oligonucleotide be able to pass through the cell membrane, and that it have a low affinity for nontarget cellular compartments and, in animal systems, nontarget organs. 

Golgi apparatus A system of flattened membrane-bounded vesicles often stacked into a complex. Numerous small vesicles are found peripheral to the Golgi and contain secretory material packaged by the Golgi. Involved in the packaging and processing of macromolecules for secretion and for delivery to other cellular compartments. 

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. 

AKAPs are a diverse family of about 75 scaffolding proteins. They are defined by the presence of a structurally conserved protein kinase A (PKA)-binding domain. AKAPs tether PKA and other signalling proteins to cellular compartments and thereby limit and integrate cellular signalling processes at specific sites. This compartmentalization of signalling by AKAPs contributes to the specificity of a cellular response to a given external stimulus (e.g. a particular hormone or neurotransmitter). 

In response to a rise up calcium, SI00 proteins interact with distinct target proteins and some members relocate to different cellular compartments and are implicated in multiple intracellular and extracellular activities. 

Very few post-translational modifications have been found on tropoelastin. However, hydroxylation of 25% of the proline residues is observed [10]. The enzymatic modification of proline to hydroxyproline (Hyp) is performed by prolyl hydroxylase [11]. The purpose of this hydroxylation remains unclear and it is even proposed that Hyps in tropoelastin are a by-product of collagen hydroxylation as this occurs in the same cellular compartment [8]. 

PROTEINS MOVE THROUGH CELLULAR COMPARTMENTS TO SPECIFIC DESTINATIONS... 

Found in various cellular compartments such as cytosol, mitochondria, and the lumen of the endoplasmic reticulum... 

Because the carotenoids favour hydrophobic domains they are generally localised in the membranes and lipoproteins of animal cells. In this location they can influence the oxidation of membrane lipids and prevent the passage of free radicals from one cellular compartment to another. Thus, DNA in the nucleus is protected from intracellularly generated ROS by (at least) the nuclear membrane and from extracellular ROS by a number of membranes. Should ROS reach the nucleus, base oxidation can occur. The base most susceptible to oxidation is guanine, although all other bases can also be affected. The cell has the ability to detect damaged bases, excise them. 

Asokan and Cho [83] reviewed the distribution of pH environments in the cell. Much of what is known in the physiological literature was determined using pH-sensitive fluorescent molecules and specific functional inhibitors. The physiological pH in the cytosol is maintained by plasma membrane-bound H+-ATPases, ion exchangers, as well as the Na+/K+-APTase pumps. Inside the organelles, pH microenvironments are maintained by a balance between ion pumps, leaks, and internal ionic equilibria. Table 2.1 lists the approximate pH values of the various cellular compartments. 

Several biochemical events occur posttranscriptionally that define the response of cells to stimuli. For instance, alternative splicing, posttrans-lational modifications, regulation of enzyme activities, distribution of metabolites between cellular compartments, necessitate analysis at the level of the proteome and the metabolome. 

The clay mineral montmorillonite, which is often used in different prebiotic syntheses, is probably now the most important mineral for experiments on prebiotic chemistry. It has shown its abilities in the area of simulation experiments on the formation of primitive cellular compartments montmorillonite accelerates the spontaneous conversion of fatty acid micelles to vesicles. Clay particles are often incorporated into the vesicle, just as is RNA, which is adsorbed at such clay particles. If the vesicles have been formed, they can continue to grow if fatty acids are fed to them via micelles. If the vesicles are pressed through 100 nm pore filters, they divide without dilution of their contents. 

Neither 79 nor 80 are detected in the intact tissue of the sponge implying that substrates and enzymes for the conversion are stored in different cellular compartments or different cell types. When isofistularin-3 (76) is the substrate, 77 is detected as a second cleavage product of this reaction. This wound-activated bioconversion is paralleled by a marked increase of biological activity of the products 79 and 80 compared to the isoxazolines. In feeding assays the aqueous... 

Here we must introduce a complication in the structures of cellular compartments. We have treated the small bacterial cells as one aqueous phase, the cytoplasm, within one containing membrane. Now there are many examples of the membrane inside the wall as a very convoluted structure with cristae reaching far... 

Both ADH and ALDH use NAD+ as cofactor in the oxidation of ethanol to acetaldehyde. The rate of alcohol metabolism is determined not only by the amount of ADH and ALDH2 enzyme in tissue and by their functional characteristics, but also by the concentrations of the cofactors NAD+ and NADH and of ethanol and acetaldehyde in the cellular compartments (i.e., cytosol and mitochondria). Environmental influences on elimination rate can occur through changes in the redox ratio of NAD+/NADH and through changes in hepatic blood flow. The equilib-... 

The fluorescence intensity of fluorescent proteins is pH dependent and most fluorescent proteins are less fluorescent at lower pH mainly because of a reduction in absorbance. Since the absorbance of the acceptor determines the FRET efficiency, changes in the acceptor absorbance spectrum due to pH variations can be wrongly interpreted as changes in FRET efficiency. Thus, a pKa well below physiological pH is recommended to prevent artifacts due to pH changes inside cells. This is especially challenging if the fluorescent proteins are to be targeted to acid cellular compartments, for example, endosomes, lysosomes, or plant vacuoles. 

Some allelochemicals such as sesquiterpene lactones or alkaloids penetrate into a cell, binding with various cellular compartments, and changing the cellular fluorescence excited by ultra-violet or violet light. This makes clear cellular mechanisms of actions for the allelochemicals. Sesquiterpene lactones azulene and proazulenes binds DNA-containing structures such as nuclei and chloroplasts, which fluoresce in blue (Roshchina, 2004). 

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