The diagrams demonstrate the basic form of the nucleotides with the bases. The compound structures are the basic building blocks of the double helix of the DNA molecule. Phosphate molecules, bonded to the deoxyribose pentose, create the outer structure.
Bonds form between the bases at the center of the helix.
Adenine and Guanine are Purine Bases. Thymine and Cytocine are Pyrimidine bases.