Abstract
This chapter discusses proteins as molecular tools. These perform an astonishing variety of functions. In addition to serving as structural materials in all living organisms, proteins are involved in diverse functions as catalysis, metabolic regulation, transport, and defence. Proteins are composed of one or more polypeptides, unbranched polymers of 20 different amino acids. The chapter looks at the genomes of organisms which specify the amino acid sequences of thousands or tens of thousands of proteins. It describes proteins as a diverse group of macromolecules that are directly related to the combinatorial possibilities of the 20 amino acid monomers. Amino acids can be theoretically linked to form protein molecules in any imaginable size or sequence.
