Stucture

Polymer, double helix of 2 polynucleotide strands bonded together by h bonds. Each nucleotide comprises of a phosphate group attached to a 5c deoxyribose sugar and an nitrogen-cotaining organic base. These bases can be either A, T, G, C. Adjacent nucleotides are joined by a condensation reaction to form the phosphate-sugar backbone of a polynucleotide strand. Two complementary strands then join by specific base pairing (A to T, C to G), which then wind together to form the double helix which provides strength and stability to the molecule. The information in DNA is encoded in the sequence of bases along the template strand. A gene is a sequence of bases on DNA that codes for the sequence of amino acids in a polypeptide chain. Proteins determine the functions and structures of cells, so DNA code controls all cell activities. Organisms of the same species carry the same genes at loci, but individuals carry different slightly different versions, alleles. Variation in these alleles results in intraspecific variation within a species.