Final answer:
DNA consists of two polynucleotide chains forming a double helix, with hydrogen bonds between complementary nitrogenous bases. Each nucleotide is made of a sugar, a phosphate group, and a nitrogenous base, with antiparallel strand orientation. Watson and Crick proposed the double helical model, fundamental for genetic information storage and transfer.
Step-by-step explanation:
The parent DNA molecule consists of two polynucleotide chains held together by hydrogen bonds between the complementary nitrogenous bases. DNA's structure is commonly referred to as a double helix, resembling a twisted ladder with the sugar-phosphate backbones as the sides and the complementary bases as the rungs. These complementary bases include adenine (A) pairing with thymine (T) and cytosine (C) pairing with guanine (G). The strands are oriented in what is known as an antiparallel fashion, meaning one strand runs in the 5' to 3' direction while the complementary strand runs from 3' to 5'. Each nucleotide is composed of a five-carbon sugar (deoxyribose), a phosphate group, and a nitrogenous base which can be either adenine, cytosine, guanine, or thymine. Covalent bonds connect the sugar of one nucleotide to the phosphate group of the next, forming the DNA strand's backbone. The specific pairing between the nitrogenous bases, facilitated by hydrogen bonding, is critical for the accurate replication and transcription processes. The double-helical shape of DNA was first proposed by James Watson and Francis Crick in 1953. This discovery was crucial in understanding how genetic information is stored and transferred within and between organisms. The sequence of the nitrogenous bases along the DNA strand forms the genetic code, which is the template for synthesizing proteins and is passed from parent to offspring during reproduction.