Tetracycline Repressor Acts as a Molecular Switch Regulated by Tetracycline Binding

Depending on their function, the biological macromolecules represented by proteins, nucleic acids (ribonucleic acid, RNA and deoxyribonucleic acid, DNA) and polysaccharides have globular or fibrous three-dimensional structures. The globular forms are mainly found for proteins and RNA (in transfer RNA and in the ribozymes) and may be considered as very complex supramolecules. Whereas proteins are composed of 20 different amino acids, RNA consists of only 4 nucleotide building blocks, and both form linear polymers several hundred to thousand units long. Proteins and RNA fold in well defined three-dimensional forms, and as such they exert their specific biological functions. The three-dimensional shape is mainly stabilized by hydrogen bonds, by van der Waals (hydrophobic) interactions and, for RNA, by stacking interactions between the 4 bases adenine, guanine, uracil, and cytosine.