The flow of genetic information is usually DNA → RNA → protein, also known as the Central Dogma of Life. MicroRNAs (miRNAs) regulate the use of mRNA. RNA also differs from DNA in that it is single-stranded and has many forms, such as messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA) that all participate in the synthesis of proteins. In RNA, uracil replaces thymine to pair with adenine (U-A). In DNA, purines pair with pyrimidines: adenine pairs with thymine (A-T), and cytosine pairs with guanine (C-G).

DNA has a double-helical structure with the two strands running in opposite directions (antiparallel), connected by hydrogen bonds and complementary to each other. DNA carries the genetic blueprint of the cell that is passed from parent to offspring via cell division.

Nucleic acids are made up of nucleotides in turn, each nucleotide consists of a pentose sugar (deoxyribose in DNA and ribose in RNA), a nitrogenous base (adenine, cytosine, guanine, and thymine or uracil), and a phosphate group. As will be explored in more detail in Chapters 14-17, DNA contains the instructions for the synthesis of proteins by dictating the sequences of amino acids in polypeptides through processes known as transcription and translation. Conserved through evolution in all organisms, nucleic acids store and transmit hereditary information. Nucleic acids (DNA and RNA) comprise the fourth group of biological macromolecules and contain phosphorus (P) in addition to carbon, hydrogen, oxygen, and nitrogen. What is the structure and roles of RNA?.

What are the two types of nucleic acid?.In this section, you will investigate the following questions:

Store and transmit genetic information