Final answer:
DNA and RNA are composed of nucleotides, which include a phosphate group, a pentose sugar, and a nitrogenous base. DNA contains adenine, thymine, cytosine, and guanine, while RNA contains adenine, uracil, cytosine, and guanine. Adenine and guanine are purines; cytosine, thymine, and uracil are pyrimidines.
Step-by-step explanation:
DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are essential molecules in the biology of living organisms. The building blocks of these nucleic acids are nucleotides, each composed of three components: one or more phosphate groups, a pentose sugar (deoxyribose in DNA and ribose in RNA), and a nitrogen-containing base. There are five primary nitrogenous bases involved in the structure of nucleic acids. In DNA, the four bases are adenine (A), thymine (T), cytosine (C), and guanine (G). Conversely, RNA contains adenine (A), uracil (U) instead of thymine, cytosine (C), and guanine (G). These nitrogenous bases are classified into two categories: purines, which are adenine and guanine and have a double-ring structure, and pyrimidines, which are cytosine, thymine (DNA only), and uracil (RNA only), and have a single-ring structure.
Within the DNA double helix, these bases pair up through hydrogen bonds, with adenine pairing with thymine (A-T), and cytosine pairing with guanine (C-G). In RNA, adenine pairs with uracil (A-U). These complementary base pairs are an integral part of DNA replication and RNA transcription processes.