ORGANIC STRUCTURE : CHEMICAL 25 



And the characters of an amino-acid, from our present point 

 of view, are the presence of the groups of atoms — 



- NH, and - COOH. 



Amino-acids Hnk together by the '' condensation " of these 

 groups thus 



NH2 - CH2- COOH + NH2 - CH - CH3 - COOH. 



Glycine | Alanine 



OH2 



The parts of the two molecules enclosed in the dotted square 

 combine, at the same time eliminating the elements of water, 



^OHo, and the result is a dipeptide. The latter has, at its ends, 



the characteristic protein linking- groups, NH, and COOH, so 

 that it can still condense with one or more amino-acid molecules, 

 to form a tri- or /)o/)'- peptide. Thus we have the next higher 

 building stones. 



Polypeptides link together (how exactly we do not know) to 

 form protein molecules. Thus 



{Arginine^ j^Arginine^ 

 Serine )■ — - Protine — etc. 

 Arginine I (Arginine) 



The. primary building stones, or amino-acids, may themselves be 

 very complex. Thus tryptophan is 



NH< >C - CH2 - CH(XH2)COOH. 



And long chains, rings and perhaps spirals of linked amino-acids 

 form the polypeptides. Obviously the protein molecule is a 

 highly complex structure and the above suggestions only faintly 

 indicate the degree of such complexity. Characteristic of the 

 proteins are (relatively to the carbohydrates and fats) the presence 

 of nitrogen (and sulphur) in the amino-acid building stones. We 

 easily see how huge molecular weights can be attained. 



r 



Carbohydrates are chains of carbon-atoms — C — which read 



as though they contain characteristic groups in certain positions 

 in the chains, although recent research shows that they have an 

 oxide ring structure. 



