Final answer:
The two strands of a DNA double helix are linked by hydrogen bonding between nitrogenous bases, with adenine pairing with thymine and guanine pairing with cytosine, while covalent phosphodiester bonds form the sugar-phosphate backbone.
Step-by-step explanation:
The two strands which make up a DNA double helix are linked to each other by hydrogen bonding between the nitrogenous bases. Each nucleotide in the DNA strand consists of a 5 carbon sugar known as deoxyribose, a phosphate group, and a nitrogenous base. The structure of DNA is characterized by two strands that twist around each other to form a right-handed helix, often likened to a twisted ladder. The nitrogenous bases of the two strands face each other and pair according to specific rules of complementary base pairing, where adenine (A) pairs with thymine (T) and forms two hydrogen bonds, and guanine (G) pairs with cytosine (C) creating three hydrogen bonds. These hydrogen bonds are crucial for the stability of the DNA double helix. Meanwhile, the sugar-phosphate backbones of the two strands, which contain the 5 carbon sugar deoxyribose and the phosphate group, are held together by phosphodiester bonds, a type of covalent bonds.
Covalent Bonds in the DNA Structure
In addition to the hydrogen bonds between the bases, it is important to note that the individual nucleotides within a single strand of DNA are connected by covalent bonds. Specifically, phosphodiester bonds link the 5' phosphate group of one nucleotide to the 3' hydroxyl group of the next nucleotide. This series of phosphodiester bonds forms the sugar-phosphate backbone of each strand, with a free phosphate group at the 5' end and a free hydroxyl group at the 3' end.