Amplification, signal

The highly variable nature of signaling pathways is also expressed by the fact that different receptors and signaling pathways can induce the same biochemical reaction in a cell. This is exemplified by the release of Ca, which can be regulated via different signaling pathways (see chapters 5-7). 

Signal pathways commonly amplify the initial signal received by the receptor during the course of the signal transduction (fig. 3.9). In many cases only a few molecules of a hormone are sufficient to initiate an enzymatic reaction in a cell, in which many substrate molecules are turned over. 

The extent of amplification, or amplification factor, varies greatly at the different levels of the signal transmission. 

An initial amplification often occurs at the level of the hormone-receptor complex. An activated receptor is capable of activating many downstream effector proteins. 

A number of stimuli are not sensed directly by the MCPs and, therefore, have somewhat modified signal transduction pathways. The most common examples follow. 

Aerotaxis is a type of energy taxis, in which bacteria respond to changes in the respiratory electron transport that result from changes in the 

therefore, seems that all the chemotactic responses, including those in which the stimuli are not sensed directly by the MCPs, are mediated by MCPs and they all share a common signal-transduction pathway. 

The life span of the hormone-receptor complex is controlled primarily by the dissociation rate of the bound hormone. 

An activated receptor can only transmit the signal further if it encounters an effector molecule. The frequency with which this occurs depends on the concentration and rate of diffusion of both components. 

The signal transmission by the hormone-receptor complex can be actively inhibited via covalent modifications (e.g., protein phosphorylation) which deactivate the hormone-receptor complex. Another mechanism for termination of signaling pathways is the internalization of the hormone-receptor complex. During internalization a section of the membrane, together with the proteins bound to it, is pinched off and transported into the interior of the cell. There the receptor can be returned to the cell membrane or be degraded. The internalization can affect the free receptor as well as the hormone-receptor complex. 

Dissolve 0.1 g calcium chloride in 100 ml distilled water and adjust pH to 7.8 with 0.1 M sodium hydroxide. Store at 37°C. 

Dissolve 0.1 g trypsin (Sigma Type II) in calcium chloride solution. 

Place sections in trypsin solution at 37°C and incubate for predetermined optimum time (approximately 20 30 min). 

The low-molecular-weight vitamin biotin is easily conjugated to antibodies and enzyme markers. Up to 150 biotin molecules can be attached to one antibody molecule, and the strong affinity of the biotin for the glycoprotein avidin allows its use as complex-ing secondary reagents. Biotin labeling of the primary (direct) or secondary (indirect) antibody can be used in the avidin-biotin methods. In the labeled avidin method the tracer is attached directly to the avidin molecule. In the avidin-biotin bridge method a biotinylated enzyme such as peroxidase is allowed to bind after attachment of avidin to the biotin-labeled antibody. 

In the avidin-biotin (ABC) method a complex of avidin and biotinylated tracer containing the free avidin binding sites is applied to the biotinylated antibody. As a high 

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It has been established, that both DN and Ibp form complex compounds with ions Eu(III), Sm(III), Tb(III) and Dy(III), possessing luminescent properties. The most intensive luminescence is observed for complex compounds with ion Tb(III). It has been shown, that complexation has place in low acidic and neutral water solutions at pH 6,4-7,0. From the data of luminescence intensity for the complex the ratio of component Tb Fig was established equal to 1 2 by the continuous variations method. Presence at a solution of organic bases 2,2 -bipyridil, (Bipy) and 1,10-phenanthroline (Phen) causes the analytical signal amplification up to 250 (75) times as a result of the Bipy (Phen) inclusion in inner coordination sphere and formation of different ligands complexes with component ratio Tb Fig Bipy (Phen) = 1 2 1. 

Fleterocycles as chemosensors in molecular wire approach to sensory signal amplification 98ACR201. 

DC amplification and pulse counting (often inaccurately called photon counting ) are two types of signal amplifications often used. 

For the detection of weak Raman lines, high laser power, high signal amplification, long pen period, and very slow scanning speed should be... 

Fig. 3a, b. Schematic representation of (a) conventional fluorescent sensor and (b) fluorescent sensor with signal amplification. Open rhombi indicate coordination sites and black rhombi indicate metal ions. The curved arrows represent quenching processes. In the case of a den-drimer, the absorbed photon excites a single fluorophore component, which is quenched by the metal ion regardless of its position... 

It has been demonstrated that dendrimers can be used also as fluorescent sensors for metal ions. Poly(propylene amine) dendrimers functionalized with dansyl units at the periphery like 34 can coordinate metal ions by the aliphatic amine units contained in the interior of the dendrimer [80]. The advantage of a dendrimer for this kind of application is related to the fact that a single analyte can interact with a great number of fluorescent units, which results in signal amplification. For example, when a Co ion enters dendrimer 34, the fluorescence of all the 32 dansyl units is quenched with a 32-fold increase in sensitivity with respect to a normal dansyl sensor. This concept is illustrated in Fig. 3. 

Based on the photoelectric effect, electrons in evacuated tubes (photoelectrons) are released from a metal surface if it is irradiated with photons of sufficient quantum energy. These are simple photocells. Photomultipliers are more sophisticated and used in modem spectrophotometers where, via high voltage, the photoelectrons are accelerated to another electrode (dynode) where one electron releases several electrons more, and by repetition up to more than ten times a signal amplification on the order of 10 can be obtained. This means that one photon finally achieves the release of 10 electrons from the anode, which easily can be measured as an electric current. The sensitivity of such a photomultiplier resembles the sensitivity of the human eye adapted to darkness. The devices described are mainly used in laboratory-bound spectrophotometers. 

Many nucleic acid detection strategies use target amplification, signal amplification or both. Invader, branched DNA (bDNA) and rolling circle amplification (RCA) are three approaches. 

The linear RCA method can use both target and signal amplification. A DNA circle (such as a plasmid, circular vims or circular chromosome) is amplified by polymerase extension of a complementary primer. Up to 10 tandemly repeated, concantemerized copies of the DNA circle are generated by each primer, resulting in one single-stranded, concantemerized product. ... 

BRANCHED DNA SIGNAL AMPLIFICATION FOR DIRECT QUANTITATION OF NUCLEIC ACID SEQUENCES IN CLINICAL SPECIMENS... 

Fig. I. Diagram of the first-generation bDNA signal amplification assay.

Both target and signal amplification systems have been successfully employed to detect and quantitate specific nucleic acid sequences in clinical specimens. Polymerase chain reaction (PCR), nucleic acid sequence-based amplification (NASBA), transcription-mediated amplification (TMA), strand displacement amplification (SDA), and ligase chain reaction (LCR) are all examples of enzyme-mediated, target amplification strategies that are capable of producing billions of... 

Chernoff, D. N., et al. (1997). Quantification of cytomegalovirus DNA in peripheral blood leukocytes by a branched-DNA signal amplification assay. J. Clin. Microbiol. 35,2740-2744. 

Collins, M. L et al. (1997). A branched DNA signal amplification assay for quantification of nucleic acid targets below 100 molecules/ml. Nucleic Acids Res. 25,2979-2984. 

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