Nucleic Acids

Nucleic Acid Bases

Adenine, cytosine, guanine, thymine, and uracil are the four main nucleic acid bases for RNA. Typically, a purine and a pyrimidine form a hydrogen bond as part of the base pair. In DNA, guanine pairs with cytosine, adenine with thymine, and uracil is substituted for thiamine.

The horizontal rods represent the pairs of bases binding the two phosphate-sugar chains together securely, while the two ribbons stand for the two phosphate-sugar chains. The fibre axis is indicated by the vertical line. The 5′ end of one strand is coupled with the 3′ end of its corresponding strand because the two strands of the helix run in the opposite directions.

Crystallography using X-rays

The triple helix