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DNA Structure - in both strands of the double helix The...

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DNA Structure As proposed by Watson and Crick,  deoxyribonucleic acid (DNA)  consists of two long nucleotide  chains. The two nucleotide chains twist around one another to form a double helix, a shape  resembling a spiral staircase. Weak chemical bonds between the chains hold the two chains of  nucleotides to one another.  nucleotide  in the DNA chain consists of three parts: a nitrogenous base, a phosphate group, and  a molecule of deoxyribose. The  nitrogenous bases  of each nucleotide chain are of two major types:  purines  and  pyrimidines . Purine bases have two fused rings of carbon and nitrogen atoms, while  pyrimidines have only one ring. The two purine bases in DNA are adenine (A) and guanine (G). The  pyrimidine bases in DNA are cytosine (C) and thymine (T). Purines and pyrimidine bases are found 
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Unformatted text preview: in both strands of the double helix. The phosphate group of DNA is derived from a molecule of phosphoric acid. The phosphate group connects the deoxyribose molecules to one another in the nucleotide chain. Deoxyribose is a five-carbon carbohydrate. The purine and pyrimidine bases are attached to the deoxyribose molecules, and the purine and pyrimidine bases are opposite one another on the two nucleotide chains. Adenine is always opposite thymine and binds to thymine. Guanine is always opposite cytosine and binds to cytosine. Adenine and thymine are said to be complementary, as are guanine and cytosine This is known as the principle of complementary base pairing....
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