Reassociation

A graph of the fraction of single-stranded DNA reannealed c/cq) as a function of CqI on a semilogarithmic plot is referred to as a c t (pronounced cot ) curve (Figure 12.20). The rate of reassociation can be followed spectrophoto-metrically by the UV absorbance decrease as duplex DNA is formed. Note that... 

FIGURE 15.21 Hormone (H) binding to its receptor (R) creates a hormone receptor complex (H R) that catalyzes GDP-GTP exchange on the o -subunit of the heterotrimer G protein (G ), replacing GDP with GTP. The G -subunit with GTP bound dissociates from the /37-subunits and binds to adenylyl cyclase (AC). AC becomes active upon association with G GTP and catalyzes the formation of cAMP from ATP. With time, the intrinsic GTPase activity of the G -subunit hydrolyzes the bound GTP, forming GDP this leads to dissociation of G GDP from AC, reassociation of G with the /Sy subunits, and cessation of AC activity. AC and the hormone receptor H are integral plasma membrane proteins G and G are membrane-anchored proteins. 

A second metallacyclobutane [F] is formed via die reassociation of terminal olefin from discrete oligomers (or monomer) with the active methylidene, produced in [E] (see above). 

Two initiation factors, eIF-3 and elF-lA, bind to the newly dissociated 40S ribosomal subunit. This delays its reassociation with the 60S subunit and allows other translation initiation factors to associate with the 40S subunit. 

Hybridization The specific reassociation of complementary strands of nucleic acids (DNA with DNA, DNA with RNA, or RNA with RNA). 

K. Ritz, B. S. Griffiths, V. L. Torsvik, and N. B. Hendriksen, Analysis of soil and bacterioplankton community DNA by melting profiles and reassociation kinetics, FEMS Microbiol. Lett. 749 151 (1997). 

The terminal (y) phosphate of GTP is hydrolyzed by the GTPase activity of the G-protein a subunit, leaving GDP bound instead. This reverses the conformational change in step 5 and allows the a subunit to dissociate from the effector and reassociate with the py subunit. The reassociation will also reverse Py-effector interaction because Ga-GDP effectively competes with the effector for Py-binding. Though of fairly high affinity (e.g.,... 

The functional activity of G proteins involves their dissociation and reassociation in response to extracellular signals 337... 

The activity of G protein Py subunits is modulated by another protein termed phosducin [16]. Phosducin is a cytosolic protein enriched in retina and pineal gland but also expressed in brain and other tissues. Phosducin binds to G protein Py subunits with high affinity. The result is prevention of Py subunit reassociation with the a subunit. In this way, phosducin may sequester Py subunits, which initially may prolong the biological activity of the a subunit. However, eventually this sequestration may inhibit G protein activity by preventing the direct biological... 

The last section of this chapter includes in brief a procedure of McF adden (9) for in situ hybridization. In situ hybridization relies on the complementarity of the bases contained within DNA and RNA. In addition to the hybridization (reassociation) of complementary DNA strands, hybridization is possible between DNA and RNA strands that are complementary. Also, hybridization is possible between a synthetic sequence and a sequence of biological origin. In situ hybridization may be used to determine the location of a specific nucleic acid sequence within a cell. The procedure requires the use of a probe for the sequence of interest. The probe, in turn, must be complementary to the sequence of interest. The probe may be either single stranded or double stranded, DNA or RNA. There must exist a method by which to detect the probe. 

For complexation/dissociation reactions, ji corresponds with the average distance that M can travel following dissociation of ML (and prior to reassociation) [40,46]. Complexes are dynamic when M frequently changes from its free to complexed state during its diffusion time to the membrane surface or, in other words, if the first-order dissociation rate constant, k(, and the pseudo first-order formation rate constant, kf[L], are much larger than their effective diffusion rate constants (D/<52) [325,326]. Thus, for conditions of planar diffusion, complexes are labile if ... 

The addition of nitric oxide markedly increases280 the rate of N2Os decomposition. In terms of the accepted mechanism, NO removes NOa in the very rapid reaction (29), thereby preventing reassociation. The stoichiometric equation is now... 

Each cycle results in a doubling of the number of strands of DNA found at the previous step. After 20 PCR cycles, the two original strands of DNA will have been amplified a millionfold (220 = 1 million), while after 30 cycles the amplification will be a billionfold. However, after 30 PCR cycles the amplification reaction reaches a plateau, primarily because of the excess of DNA synthesized (substrate excess), competition by nonspecific products, and reassociation of product. Figure 3 is a diagrammatic representation of PCR. A few selected analytical variables affecting PCR need to be considered. First, the reannealing temperature is critical to the specificity of the amplification. Low temperatures of between... 

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