Final answer:
The DNA molecule is comprised of two antiparallel strands forming a double helix, with a backbone made of sugar and phosphate groups. Nucleotides, consisting of a 5-carbon sugar, phosphate, and nitrogenous base, pair through hydrogen bonds—adenine with thymine and cytosine with guanine—to stabilize the structure.
Step-by-step explanation:
Structure of DNA
DNA, or deoxyribonucleic acid, has a distinctive double-helical structure. This structure consists of two long strands of nucleotides that twist around each other like a twisted ladder. Each nucleotide is composed of three parts: a 5-carbon sugar (deoxyribose), a phosphate group, and a nitrogenous base. In DNA, there are four types of nitrogenous bases: adenine (A), thymine (T), cytosine (C), and guanine (G).
The sugar and phosphate groups of the nucleotides form the backbone of the DNA strand, with the phosphate of one nucleotide covalently bonded to the sugar of the next. These covalent bonds are called phosphodiester bonds. The two strands of DNA are oriented in opposite directions, known as antiparallel orientation. In this arrangement, the 5' end of one strand is aligned with the 3' end of the other, which is significant for DNA replication and function.
Inside the double helix, the nitrogenous bases from one strand hydrogen bond with the bases of the complementary strand. Adenine pairs with thymine via two hydrogen bonds, while cytosine pairs with guanine via three hydrogen bonds. These pairs are often referred to as base pairs and are like the rungs of a ladder. The hydrogen bonds are responsible for the specific pairing and the high-fidelity of DNA replication, contributing to the stability of the DNA molecule.
The DNA's double-helix structure is stabilized by the hydrogen bonds between complementary bases and the hydrophobic interactions between the bases in the center of the helix. The overall structure of DNA is such that the hydrophilic backbones face the external aqueous environment, while the hydrophobic bases are protected on the inside, contributing to the polar nature of the strands.