A Molecular Graphics companion to an Introductory Course in Biology or Biochemistry. Copyright 1995, Richard B. Hallick. Pyrimidine Bases Deoxyribose Sugar Nucleosides Nucleotides Base Pairs DNA Backbone DNA Double Helix DNA Helix Axis Components of DNA DNA is a polymer. There are four different types of nucleotides found in DNA, differing only in the nitrogenous base. The four nucleotides are given one letter abbreviations as shorthand for the four bases.
T is for thymine Purine Bases Adenine and guanine are purines.
All ring atoms lie in the same plane. Pyrimidine Bases Cytosine and thymine are pyrimidines. Like purines, all pyrimidine ring atoms lie in the same plane. The deoxyribose sugar of the DNA backbone has 5 carbons and 3 oxygens. The carbon atoms are numbered 1', 2', 3', 4', and 5' to distinguish from the numbering of the atoms of the purine and pyrmidine rings.