Double-hairpin

Two types of single-stranded, intramolecular triple helices of the type shown in Figure 12(d) are possible by double-hairpin formation [37]. This was demonstrated for the R RY motif by the design of suitable 18-mer sequences containing two G tracts to fold in an antiparallel fashion. The salient features of this intramolecular triplex motif are that (1) Mg2+ is not essential, (2) compared to the intermolecular version, a shorter triplex stem can be formed in a much lower DNA concentration, and (3) acidic conditions are not required as it is the R-RY motif. The evidence for triplex existence came from the observation that duplex-hairpin intercalator binders such as actinomycin D, chromomycin Aj and ethidium bromide bind poorly. 

The Ballestra group uses a combination of U-tube cooler and a shell-and-tube heat exchanger for the cooling of S02/air with ambient air. MM and Mazzoni supply a vertical double-hairpin heat exchanger (a so-called trombone cooler) with air cooling. 

Design a double hairpin ("trombone") cooler to cool the S02/air ex sulphur furnace to a temperature of 430with ambient air flowing counter-current through the jacket of the trombone cooler inlet cooling air temperature 30 "C, outlet 250 C. Mean SOi/air flow velocity in tube 25 m/s, mean cooling air velocity in jacket 20 m/s. 

Calculate the lagging of the double hairpin heat exchanger assuming a heat conductivity coefficient, k, of the glass wool insulation material of 0.15 W/m°C and a heat transfer coefficient ha (W/m C) from the Al-cladding to the ambient air of 25 W/m C. 

Make a sketch of the double hairpin cooler with expansion pieces. 

A pseudoknot is a double-hairpin structure with an extended quasi-continuous double-helical stem region (Fig. 1.15). It is formed when bases outside a hairpin structure pair with bases within the hairpin or internal loop (111,112). The pseudoknot is a potentially important tertiary structural motif of RNA and it has been identified in 16S rRNA, U2 snRNA, and some plant viral RNAs with tRNA-... 

TABLE 11-15 Double-Pipe Hairpin Section Data... 

Used by permission Bui. Application and Design Estimating of Double Pipe and Hairpin Exchangers. Brown Eintube Co., A Koch Engineering Co., Houston, Texas. 

Mrksich, M., M.E. Parks, and P.B. Dervan. Hairpin peptide motif A new class of oligopeptides for sequence-specific recognition in the minor-groove of double-helical DNA. J. Am. Chem. Soc. 1994, 116, 7983-7988. 

RNA exists as a single strand, whereas DNA exists as a double-stranded helical molecule. However, given the proper complementary base sequence with opposite polarity, the single strand of RNA—as demonstrated in Figure 35-7—is capable of folding back on itself like a hairpin and thus acquiring double-stranded characteristics. 

Hairpin A double-helical stretch formed by base pairing between neighboring complementary se-... 

In general for the C20 series, maximal activity is achieved with amides of arachidonic acid (1) [81], mead acid (199) [149], and dihomo-y-linoleic acid (200) [150] (see Table 6.18). Decreasing the unsaturation (201), (202), or abolishment of the n-pentyl chain (203) [150] led to less active or inactive compounds. Variable results were seen with longer chains. The C22 4 n-6 analogue (204) is as active as AEA (1) whereas the C22 6 n-3 analogue (205) is less active than the C20 5 n-3 analogue (203) [150]. Replacement of the double bonds with triple bonds (206) resulted in loss of activity [150] (see Table 6.18). Forcing the fatty acid chain into a hairpin conformation by cyclisation (207) also resulted in inactive compounds [151]. 

Incorporation of an artificial flavin nucleobase and of a cyclobutane pyrimidine dimer building block into DNA DNA double strands, DNArPNA hybrid duplexes, and DNA-hairpins, provided compelling evidence that an excess electron can hop through DNA to initiate dimer repair even at a remote site. The maximum excess electron transfer distance realised so far in these defined Donor-DNA-Acceptor systems is 24 A. New experiments are now in progress to clarify whether even larger transfer distances can be achieved. 

Stem A stretch of double-stranded RNA Loop A loop of RNA Hairpin loop A very short loop... 

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