Foods : their origin, composition and manufacture / by William Tibbles.

  • Tibbles, William, 1859-1928.
Date:
1912
Catalogue details

Licence: In copyright

Credit: Foods : their origin, composition and manufacture / by William Tibbles. Source: Wellcome Collection.

Provider: This material has been provided by The University of Leeds Library. The original may be consulted at The University of Leeds Library.

    32/972 page 20
    Still further substitution occurs in serin by hydroxyl replacing another atom of hydrogen, or in cystein by that atom being replaced by the ion SH. . The true proteids or albuminous substances exist in a livmg and a non-living form. The former are the most interesting substances known to the chemist, but our knowledge of them is practically nil. They consist of exceedingly complex molecules of a very unstable character, and in a state of constant change—i.e., of being built up and broken down by the physio-chemical processes of the living organism. At the moment of death, however, their character changes: they become more stable and are capable of being m- vestigated. In such a condition they are more properly called proteins. They undergo hydrolytic cleavage by means of reagents or enzymes, and the products of that cleavage chiefly include the amino-acids. We do not know how these are Imked together to form the protein molecule; but they are probably pined m the ether fashion—that is, by junction of the alkyl part of theu: alcohol r3,(3.1C3fls • Of the importance of amino-acids in the construction of proteins there can be no doubt whatever. Aspartic acid or asparagin (its derivative) and phenylalanin are present m most animal and vegetable proteins ; tyrosin and prolm, m all animal protems gllcocoU forms 25 per cent, of elastin ; leucm forms 10 per cent, of cS 15 per cent, of fibrin, 20 per cent, of serum a bumm, 21 per cent of elastin, and 29 per cent, of h^emoglobm ; glutammic acid f orms 8 per cent, of sen?m globulm, 8 per cent, of egg-albumm, 10 per cent of casein, and 30 per cent, of ghadm. The ad]ommg table chnw.; the Dercentage of araino-acids m various protems. The proS mokcule is not entirely composed of ammo-acids, for some proteins liave a carbohydrate group m their structure. TOs howewr!^ always an amino-sugar, usuaUy sluoo^a'™. ,;n£H to the protein in a glucoside-hke combmation Carbo- Wdrate cai be'^^Sed by fhe hydrolytic cleavage of protems inSl-fte-cS..7jt?^ lis?^i?ys^,?Str'pt^^^^^^ 1ra:fi5,?KS:j:^«cCund.^^^^^ chain together
    digitised image 1
    digitised image 2
    digitised image 3