24.09.2026 15.13

DNA is a large molecule, often referred to as a giant molecule because it is composed of very, very many atoms. The building blocks of DNA are called nucleotides. Each nucleotide consists of a sugar molecule called deoxyribose, a phosphate group, and one of four organic bases. The four organic bases are adenine, thymine, cytosine, and guanine. Each organic base pairs with another in a complementary manner. This means they fit together like a key and a lock, forming a pair. The pairs are adenine and thymine, which are connected by two hydrogen bond bridges. The other pair is cytosine and guanine, which are connected by three hydrogen bond bridges. The DNA structure resembles a double helix, and the side of the helix is always alternating between sugar and phosphate groups. The strands of the DNA double helix are formed by the complementary base pairs, which are adenine and thymine, and the other cytosine and guanine.