Human DNA, Double helix model Mounted on a base. Usage This model was made according to the technical index of 'Model of DNA Structure' published by National Education Department. It is a demonstration model for biology teaching in high school, can also be used for college students majoring in biology. Demonstration Contents 1, this model is a teaching demonstration model of a type B DNA molecule structure enlarged by 0.1 billion times. 2, DNA molecule is formed by two nucleotide chains right-hand helically coiling an axis. 3, The two nucleotide chains are parallel but have opposite directions. One is 5'→3'; another one is 3'→5'. 4, The main chains formed by phosphate radical and deoxyribose are outside of the helix.the basic groups are inside. The basic groups are almost vertical to the axis, while the deoxyribose is parallel to the axis. 5, The bases from the two chains form a group via hydrogen bonds. The two groups are A--T and G--C. There are 2 hydrogen bonds between a A--T group; 3 hydrogen bonds between a G--C group. Red pipes in the model indicate hydrogen bonds. 6, The surface of the helix has two obvious grooves; one is big and deep, another is small and shallow; they are called major groove and minor groove.