Final answer:
DNA is an organic double helix structure composed of nucleotides. Each nucleotide contains a nitrogenous base, deoxyribose sugar, and a phosphate group. These nucleotides pair via hydrogen bonds, A with T and C with G, resulting in the double helix structure responsible for genetic encoding.
Step-by-step explanation:
Structure of DNA and Nucleotide Composition
The structure of DNA is fundamental to the genetics of all living organisms. DNA, or deoxyribonucleic acid, is an organic molecule characterized by its double helix form. Nucleotides are the building blocks of DNA, comprising a nitrogenous base, a five-carbon sugar (deoxyribose), and a phosphate group. The DNA double helix is formed by two strands of DNA wound around each other, connected by hydrogen bonds between the nitrogenous bases. There are four types of nitrogenous bases in DNA: adenine (A), thymine (T), cytosine (C), and guanine (G). The backbone of each DNA strand is made of a repeating pattern of sugar and phosphate groups. During DNA replication, which occurs before a cell divides, each strand serves as a template for the creation of a new complementary strand, with adenine pairing with thymine and cytosine pairing with guanine, a principle known as base pairing. This process is referred to as semi-conservative because each new DNA molecule conserves one of the original strands and includes a new, complementary one. The composition and sequence of nucleotides in a DNA molecule determine the genetic instructions used in the development, functioning, and reproduction of organisms.