Adenosine triphosphate (ATP) is a molecule generated during intracellular oxidation of glucose and which stores energy. By enzymatic transfer of phosphate, the energy is also transferred.

Cyclic adenosine monophosphate (cAMP) is generated from ATP by adenylate cyclase . Adenylate cyclase is, for example, stimulated by the hormone glucagon. Within the cell, cAMP has function a hormone has in the organism: it is a messenger. With hormones seen as primary messengers, cAMP is the prototype of second messengers. Other second messengers are cyclic guanosine monophosphate, diacyl glycerol , inositol trisphosphate, and nitrogen monoxide.

Enzymes are protein molecules performing chemical reactions.

A cell consists of amino acids, proteins, glycerol derivatives, fatty acids, lipids, large and small sugar molecules, deoxyribonucleic acid (DNA), ribonucleic acid (RNA), and a multitude of other substances, such as vitamins, salts, trace elements, and other organic compounds. To obtain information about all these substances, please consult a biochemistry textbook.

Nucleic acids are built with a chain where a sugar and a phosphate alternate. To each sugar a so-called base is linked, the sequence of the base determining genetic information. Two different sugars are used differing from each other by a single oxygen atom. Genetic information in all living cells from bacteria to plants to animals consists of DNA using deoxyribose with four bases—adenine, cytidine, guanine, and thymine. Within the cell, information from the cellular nucleus is transcribed into RNAs built with a ribose phosphate backbone and where together with adenine, cytidine and guanine, uracil is used instead of thymine. There are functionally different RNAs: messenger RNA (mRNA), ribosomal RNA, and transfer RNA (tRNA).

In viruses, genetic information consists of DNA or RNA.

Proteins are described in detail in Chap. 4