Summary
Highlights
Nucleotides are monomers composed of a pentose sugar, a nitrogenous base, and a phosphate group. They join together via condensation reactions to form polynucleotides, releasing water and forming phosphodiester bonds, which create a sugar-phosphate backbone. Polynucleotides can be broken down through hydrolysis reactions.
DNA is a double helix with two polynucleotide strands. Each DNA nucleotide contains deoxyribose sugar, a phosphate group, and one of four nitrogenous bases: adenine, guanine (purines), cytosine, or thymine (pyrimidines). Complementary base pairing occurs, with adenine always pairing with thymine (two hydrogen bonds) and cytosine with guanine (three hydrogen bonds). The two strands run antiparallel to each other.
DNA primarily stores genetic information for protein synthesis and passes this information between generations. Its structure is well-suited for these roles: the sugar-phosphate backbone protects the bases, it's double-stranded for replication, it's a large molecule for information storage, the double helix makes it compact, complementary base pairing ensures accurate replication, and weak hydrogen bonds allow strands to separate easily for replication.
RNA's main function is to use information from DNA to synthesize proteins. While similar to DNA, RNA has several key differences: it contains ribose sugar instead of deoxyribose, uracil instead of thymine as a base, is typically single-stranded, and is generally much shorter than DNA molecules.