96 



UNITY AND DIVERSITY IN BIOCHEMISTRY 



polypeptide chains with the a-helical structure are arranged in parallel with 

 each other. In other proteins they are themselves associated in threads in 

 which the polypeptide chains are twisted together (Fig. 10). 



(b) Globular Proteins 



A profound study of the many globular proteins has been carried out 

 over the last few years, information being obtained from the study of osmo- 

 tic pressure, diffusion, viscosity, sedimentation, electrophoresis, light 



Fig. 9 (Pauling, Corey and Branson) — Portion 



of a-helix. 



N = nitrogen atom; R = side chain; black dots 



= hydrogen atoms ; blank circles = carbon atoms ; 



dotted circles = oxygen atoms; dotted lines = 



hydrogen bonds. 



diffraction, birefringence of flow, dielectric properties, infra-red absorption, 

 X-ray diffraction and by the use of the electron microscope. This imposing 

 array of techniques has provided an immense amount of data the systemiza- 

 tion of which remains almost impossible. Certain general conclusions, 

 however, may be drawn from these results. 



