Double helix hydrogen bonds

Fic. 10.—Parallel packing arrangement of 6-fold, A-amylose (8) molecules, (a) A stereo side view of less than 2 turns of a pair of double helices 10.62 A (=al2) apart. The two strands in each helix are distinguished by open and filled bonds, and the helix axis is also drawn, for convenience. Note that atom 0-6 mediates both intra- and inter-double helix hydrogen bonds. 

Fig. 30. — Packing arrangement of 4-fold antiparallel double helices of potassium hyaluronate (32). (a) Stereo view of a unit cell approximately normal to the line of separation of the two helices. The two chains in each duplex, drawn in open and filled bonds for distinction, are linked by not only direct hydrogen bonds, but also water bridges. Inter double-helix hydrogen bonds are mediated between hydroxymethyl and iV-acetyl groups. Potassium ions (crossed circles) at special positions have only a passive role in the association of hyaluronate chains.

Figure 6. Molecular drawings of the best arrangement of two anti-parallel double-helices, a) Projection perpendicular to the chain axis, b) Projection along the chain axis. Inter double-helix hydrogen bonds are shown as dotted lines.

FIGURE 1 5.22 Complementary hydrogen bonding in the DNA double helix. Hydrogen bonds in the thymine-adenine (T—A) and cytosine-guanine (C—G) pairs stabilize the double helix. 

In a DNA double helix, hydrogen bonding occurs between... 

Fig. 10.23 Three examples of zipper type junction zones double helix, hydrogen-bonded ladder (with small loops), and eggbox junction. (Reprinted with permission from Ref. [67].)...

Figure 1. The four base pairs used to construct the double helix hydrogen bonds (IIIII).

Figure 7.24 The a-helix (a) the succession of carbon and nitrogen atoms along the backbone of an a-helix, hydrogen bonds form between O atoms on carbon and H atoms on nitrogen linked by dashed lines, R represents a general organic side-group and for clarity not all hydrogen atoms are shown (b) schematic depiction of the coiled a-helix, with four hydrogen bonds indicated by double headed arrows (c) cartoon depiction of an a-helix as a coiled ribbon...

Section 28 8 The most common form of DNA is B DNA which exists as a right handed double helix The carbohydrate-phosphate backbone lies on the outside the punne and pyrimidine bases on the inside The double helix IS stabilized by complementary hydrogen bonding (base pairing) between adenine (A) and thymine (T) and guanine (G) and cytosine (C)... 

Double helix (Section 28.8) The form in which DNA normally occurs in living systems. Two complementary strands of DNA are associated with each other by hydrogen bonds between their base pairs, and each DNA strand adopts a helical shape. 

FIGURE 1.5 The DNA double helix. Two complementary polynucleotide chains running in opposite directions can pair through hydrogen bonding between their nitrogenous bases. Their complementary nucleotide sequences give rise to structural complementarity. 

FIGURE 10.41 (a) Gramicidin forms a double helix in organic solvents a helical dimer is the preferred strnctnre in lipid bilayers. The strnctnre is a head-to-head, left-handed helix, with the carboxy-termini of the two monomers at the ends of the strnctnre. (b) The hydrogen-bonding pattern resembles that of a parallel /3-sheet. 

The DNA isolated from different cells and viruses characteristically consists of two polynucleotide strands wound together to form a long, slender, helical molecule, the DNA double helix. The strands run in opposite directions that is, they are antiparallel and are held together in the double helical structure through interchain hydrogen bonds (Eigure 11.19). These H bonds pair the bases of nucleotides in one chain to complementary bases in the other, a phenomenon called base pairing. 

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