Hydrogen bonding plays a crucial role in maintaining the stability of the double helix structure of DNA. DNA, or deoxyribonucleic acid, is composed of two polynucleotide chains that coil around each other to form a double helix. Each polynucleotide chain consists of nucleotide units, which are composed of a sugar molecule deoxyribose , a phosphate group, and a nitrogenous base. There are four types of nitrogenous bases in DNA: adenine A , guanine G , cytosine C , and thymine T .The stability of the double helix structure is primarily due to the complementary base pairing between the two polynucleotide chains. The bases on one chain pair with the bases on the other chain through hydrogen bonds. Adenine pairs with thymine A-T and guanine pairs with cytosine G-C . This specific base pairing is known as Watson-Crick base pairing.The chemical structure of the nucleotide bases allows for this complementary base pairing and formation of base pairs through hydrogen bonding. Adenine and guanine are purines, which have a double-ring structure, while cytosine and thymine are pyrimidines, which have a single-ring structure. The hydrogen bonds formed between the bases are as follows:1. Adenine A forms two hydrogen bonds with thymine T .2. Guanine G forms three hydrogen bonds with cytosine C .These hydrogen bonds provide the specificity and stability required for the formation of base pairs. The purine-pyrimidine pairing ensures that the distance between the two polynucleotide chains remains constant, maintaining the uniform width of the DNA double helix.In summary, hydrogen bonding plays a vital role in maintaining the stability of the double helix structure of DNA by enabling the specific and complementary base pairing between the two polynucleotide chains. The chemical structure of nucleotide bases allows for the formation of base pairs through hydrogen bonds, ensuring the uniform width and overall stability of the DNA double helix.