Basic Notions in Molecular Biology
Every living organism is a complex entity that is composed of cells. Each cell contains several compartments and many different molecular components with different roles. The functioning of a cell is an orchestrated sequence of events that are carried out to sustain life, respond to surrounding stimuli and communicate with other cells. Proteins are the molecules that form much of the functional machinery of each cell in every organism. Proteins include the enzymes that catalyze chemical reactions and regulate a variety of biochemical processes in the cell, as well as antibodies that defend the body against infections. Proteins that are evolutionarily related usually have the same core structure, but they may have very different loops. A protein family is a group of homologous proteins, and proteins that belong to the same family have the same or very similar biological function. Protein families that are distantly related through evolution are usually grouped into a protein superfamily.