Sentence:  The unstained strips were then marked , using the stained ones as a guide , and cut transversely so as to separate the various <WSD>protein</WSD> bands . 
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