DNA Structure

The structure of DNA Deoxyribonucleic acid is a linear polymer of up to a hundred million monomer units (nucleotides). DNA contains only four different nucleotides. A nucleotide has only three parts, a phosphate group, 2-Deoxyribose, and an organic base. The structures of 2-Deoxyribose and of the bases are shown below. A purine has a pair of fused rings; a pyramidine has only one ring. Both purines and pyramidines are heterocyclic, i.e. the rings are …

…For example, the adenylate residues, if all are on one strand, in an A-T rich region of DNA, stack at a greater angle to the helix axis than the thymidylate residues on the opposite strand, leading to bending of the DNA. Bent DNA is important because it accommodates binding proteins. Cellular DNA molecules in eukaryotes are linear, but all bacterial and many viral DNAs are circular. Circular DNA is also found in mitochondria and chloroplasts.