15:3/ X-ray Analyses of Proteins and Nucleic Acids 277 



Amino Acid Structure 



Abbreviation 

 Molecular for residue 



weight in proteins 



H O 



I / 

 CH 2 — CH 2 — CH 2 — C— C 



17. Citrulline j 75 ~ t _ 



H 2 N— C— NH NH 2 OH 



O 



H 



H 

 -CH 2 — C — C 



18. Histidine HN^ ^^N NH 2 OH 155 — his- 



H 



19. Proline H 2 <^ — C 115 — pro- 



OH 



H OH 



H 2 

 20. Hydroxyproline \ /* 131 — hypro- 



H 



3. Nucleic Acids 



As recently as 1950, many scientists regarded proteins as the funda- 

 mental "stuff' 1 of life, controlling reactions, contracting, transmitting 

 genetic information, and reproducing themselves. This view has given 

 way to one which assigns proteins to a more restricted role but emphasizes 

 the importance of the nucleic acids in protein synthesis and genetic 

 transmission of information. The nucleic acids are high polymers, just 

 as are proteins, but are given a separate name because the monomers 

 from which nucleic acids are built are not amino acids. Consisting of 

 different structural units, the nucleic acids differ significantly from 

 proteins in their physicochemical properties, as well as in their biological 

 action. 



The monomers from which nucleic acids are polymerized are called 

 nucleotides. Each nucleotide consists of a nucleoside condensed by the 



