Phosphate double helix

FIGURE 28 5 (a) Tube and (b) space filling models of a DNA double helix The carbohydrate-phosphate backbone is on the out side and can be roughly traced in (b) by the red oxygen atoms The blue atoms belong to the purine and pyrimidine bases and he on the inside The base pairing is more clearly seen in (a)... 

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)... 

Figure 7.1 Schematic drawing of B-DNA. Each atom of the sugar-phosphate backbones of the double helix is represented as connected circles within ribbons. The two sugar-phosphate backbones are highlighted by orange ribbons. The base pairs that are connected to the backbone are represented as blue planks.

DNA is made up ot two intertwined strands. A sugar-phosphate chain makes up the backbone of each, and the two strands are joined by way of hydrogen bonds betwen parrs of nucleotide bases, adenine, thymine, guanine and cytosine. Adenine may only pair with thymine and guanine with cytosine. The molecule adopts a helical structure (actually, a double helical stnrcture or double helix ). 

The first one consists of 11-12 water molecules per nucleotide unit, which are coordinated directly to sites of the DNA double helix. Two of these water molecules are bound very tightly to the ionic phosphate residue and cannot be removed without completely destroying the structure of DNA. There are four other water molecules... 

DNA consists of two strands of sugar-phosphate backbones wound around each other in a double helix. The two helices are connected by hydrogen bonds between the bases. 

The two complementary strands of the DNA double helix run in antiparallel directions (Fig. 4-1). The phosphodiester connection between individual deoxynucleotides is directional. It connects the 5 -hydroxyl group of one nucleotide with the 3 -hydroxyl group of the next nucleotide. Think of it as an arrow. If the top strand sequence is written with the 5 end on the left (this is the conventional way), the bottom strand will have a complementary sequence, and the phosphate backbone will run in the opposite direction the 3 end will be on the left. The antiparallel direc-... 

In forming the double-helix polymeric DNA structure, the two sugar-phosphate backbones twist around the central stack of base pairs, generating a major and minor groove. Several conformations, known as DNA polymorphs, are possible. 

Two examples of aquation/anation studies of chloro-platinum(II) complexes of possible medical relevance appeared in subsection 1 above 202,207). Aquation of cisplatin is slower in the presence of DNA but not in the presence of phosphate 220). DNA also inhibits substitution in [Pt(terpy)(py)]2+ and related complexes. For reaction of these charged complexes with iodide ion inhibition is attributable to electrostatic interactions - the complex is concentrated on the double helix and thus separated from the iodide, which distances itself from the helix. Intercalation of these complexes within the helix also serves to make nucleophilic approach by neutral reagents such as thiourea more difficult 221). 

Watson and Crick showed that the normal structure of DNA consists of a double helix made from two single oligonucleotide strands. The two sugar-phosphate strands of the helix run in opposite (anti-parallel) directions and the bases point... 

DNA is a double helix formed by base pairs attached to a sugar-phosphate backbone. 

Nucleotides are joined into a chain formation, as illustrated in Fig. A2.6a. In DNA, two nucleotide chains intertwine around each other in a double helix formation (Fig. A2.6b). The backbone of the two strands is the phosphate-sugar linkage. 

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