ABSTRACT
Proteins: an overview Proteins are the most versatile macromolecules in living organisms and carry out a diverse array of functions. They transport and store other molecules (e.g. hemoglobin and myoglobin; Section B3), they provide mechanical support (e.g. collagen; Section B4), they generate movement (e.g. actin and myosin; Section B5), they provide immune protection (e.g. antibodies; Section B6), they act as catalysts (enzymes; Sections D1-D5), they are involved in cellular signaling (Section E5), and they transmit nerve impulses (Section E6). Each protein has a unique amino acid sequence that is genetically determined (Section H1). Most proteins contain between 50 and 2000 amino acids linked together via peptide bonds. With the average molecular weight of an amino acid being about 110 (Table 1 in Section B1), the molecular weights of most proteins are between 5500 and 220 000. We can also refer to the mass of a protein, which is expressed in units of Daltons, where one Dalton is equal to one atomic mass unit. Thus, a protein with a molecular weight of 25 000 has a mass of 25 000 daltons or 25 kDa.
