The sugar will be one of two very similar pentose rings. Ribonucleic acids contain the sugar ribose. Deoxyribonucleic acids contain the sugar deoxyribose. The only difference between these two sugars is that deoxyribose contains one oxygen atom less than ribose. Pentose sugars are essential because they are involved in linking different nucleotides together by condensation reactions. The Nitrogen-Containing Bases
There are two types of bases found in nucleic acids. The purine bases have two nitrogen containing rings, while the pyrimidines have only one. In DNA the purines are adenine (A) and guanine (G) and the pyrimidines are cytosine (C) and thymine (T). In RNA the purine bases are the same as in DNA, but the pyrimidines are cytosine and uracil (U). These rings have the chemical property of being bases because of the nitrogen atoms they contain. Adenine always forms 2 hydrogen bonds with thymine.
Cytosine always forms 3 hydrogen bonds with guanine.
The phosphate group gives nucleotides, and the nucleic acids that they make up, their acidic character. The phosphate group is chemically reactive and allows new groups to be added by condensation reactions. More complex strands can be built up, and the nucleotides can be linked together to form a polynucleotide chain. These three components when joined form a nucleotide:
The three parts of a nucleotide monomer are joined by condensation reactions. Two molecules of water are removed in the process.