Sentence:  In the thyroid gland it appears that <WSD>proteins</WSD> ( chiefly thyroglobulin ) are iodinated and that free tyrosine and thyronine are not iodinated . 
Meaning of the word marked with <WSD> tags:  any of a large group of nitrogenous organic compounds that are essential constituents of living cells; consist of polymers of amino acids; essential in the diet of animals for growth and for repair of tissues; can be obtained from meat and eggs and milk and legumes