Polymers such as proteins, polysaccharides and nucleic acids are formed when monomers link in long chains. The different types of bonds provide structure and stability to biomolecules and make them functional. Proteins are formed from amino acids when the carboxyl group of an amino acid reacts with the amino group of the next amino acid and form a peptide bond. This bond is formed due to dehydration. Polysaccharides are formed when several monosaccharides linked together by a glycosidic bond. This bond is also formed due to dehydration. The glycosidic bond connects carbohydrate molecules or a carbohydrate and a non-carbohydrate molecule. Nucleic acids are formed when a nitrogenous base, a phosphate group and a pentose sugar are linked to form a polynucleotide chain. Here, the three prime carbon atoms of one sugar of a nucleotide are linked to the five prime carbon atoms of the sugar of the succeeding nucleotide by a phosphate moiety. The phosphate and hydroxyl groups of sugar join to form an ester bond. The ester bonds formed by the phosphate group, between the third and fifth carbon atoms of adjacent pentose sugar rings, are called phosphodiester bonds. This bond links three prime carbon atoms of one sugar molecule with the five prime carbon atoms of an adjacent sugar molecule. The phosphodiester bond forms the backbone of the DNA strands.
The B-form of the DNA exists as a double helix, where two strands of polynucleotides are anti-parallel, that is, one strand runs in three prime to five prime and the other strand runs in five prime to three prime directions. The backbone of the DNA is formed by a sugar-phosphate-sugar chain. The four bases found in the DNA are adenine, cytosine, guanine and thymine. Adenine on one strand base pairs with thymine on the other strand by a double bond. Similarly, cytosine on one strand base pairs with guanine on the other strand by a triple bond. One full 360o turn of the helical strand would involve ten base pairs. The distance along one turn is known as a pitch, which is thirty-four angstroms. The distance between two base pairs is three-point four angstroms.