Structure of the Double Helix

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 ). 

Examine DNA. How many base pairs does it contain Starting from one end, write down the sequence of bases in one strand. Write down the sequence in the complementary strand. Is this a proper DNA fragment, or does it contain base-pair mismatches  

How many base pairs are required for a full (360°) turn of the helix Locate the minor and major grooves in the DNA fragment. Will a polycyclic aromatic hydrocarbon such as anthracene be able to fit into the major grove Examine space-filling models to tell. 

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Figure 2.5 (a) The structure of the double helix at the heart of DNA. The slender rods represent the hydrogen bonds that form between the organic bases situated on opposing strands of the helix, (b) Hydrogen bonds (the dotted lines) link adenine with thymine, and guanine with cytosine... 

Question The structure of the double helix shown in Fig. 7-3 is called the B form. What are the other forms, and do they have a biological role ... 

In this chapter, we will describe the coordination properties of nucleic acids, including the consequences on metal interactions of the polyanionic nature of oligonucleotides and the supra-molecular structure of the double-helix. Types of metal sites found in other structures such as G-quartets and complex RNA folds will be described. Small coordination compounds between metals and nucleotides, the monomeric units of polymeric DNA and RNA, have been widely studied and also are included in this review. While the majority of material included in the review is derived from X-ray crystallographic studies, some information from spectroscopy and other physical methods is included where illuminating. 

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