the chief nitrogenous constituents of living organisms. They contain about 50% carbon, about 25% oxygen, about 15% nitrogen, about 7% hydrogen and some sulphur. They are formed from a mixture of amino-acids which they give on hydrolysis. Proteins are precipitated by alcohol, propanone and by strong solutions of salts. They give certain colour reactions which are caused by the presence of specific amino-acids in the molecule., ühest või mitmest peptiidahelast koosnev suuremolekuliline ühend ehk makromolekul (nt. ensüümid, struktuurivalgud)