The size of a synthesized protein can be measured by the number of amino acids it contain and by its total molecular mass , which is normally reported in units of daltons ( synonymous with atomic mass units ) , or the derivative unit kilodalton ( kDa ) . Yeast proteins are on average 466 amino acids long and 53 kDa in mass . The largest known proteins are the titins , a component of the muscle sarcomere , with a molecular mass of almost 3 @,@ 000 kDa and a total length of almost 27 @,@ 000 amino acids .