THE SYNTHESIS OF PROTEINS 47 



tion of ammonia and hydrocyanic acid upon an aldehyde 

 a simple acid might be formed, thus: 



CH3COH + HCN + NH4OH = 



acetaldehyde ammonia 



CH3— CH— NH2— COOH + NH3 



"^ v^ ' ammonia 



alanin 



Such a synthesis may take place in leaves. During the 

 hours of daylight aldehyde formation may occur as a part 

 of the process of photosynthesis (see Chap. IV). At the 

 same time, a part of the ammonia derived from the ni- 

 trate and nitrite may be converted into hydrocyanic acid. 

 This may combine with the aldehyde which is being 

 formed at the same time. While this conjecture as to 

 the nature of the process may not prove to be correct in 

 all its details, it suggests a very promising line for 

 investigation. 



The Synthesis of Proteins from Amino- Acids. — 

 Proteins have actually been synthesized from amino- 

 acids and amino-acids are always found in food solutions 

 on their way to parts where protein is being stored or 

 protoplasm is being constructed, yet nothing or almost 

 nothing is known about the change which takes place 

 in the body of the plant. The amino-acids disappear 

 and the complex proteins appear instead. It is probable 

 that any normal plant cell can make the proteins which 

 it requires, if it receives suitable carbohydrates and 

 amino-acids for construction. There is no evidence to 

 show that protein-synthesis takes place more rapidly in 

 one part of the plant than another. The amino-acids 

 may be made chiefly in or near the chlorophyll-containing 

 cells in which the carbohydrates are formed in daylight, 

 though the formation of protein appears to be quite 

 independent of light. 



We may conceive the process of protein-synthesis from 

 amino-acids taking place along a series which starts with 

 glycerose (CaHeOa), lactic acid (also CaHcOa), and one 



