276 



UNITY AND DIVERSITY IN BIOCHEMISTRY 



Fig. 83 (Frey-Wyssling) — Types of link between neighbouring polypeptide chains. 



O = a water molecule. 



4. Homopolar valencies 



These can be formed in a variety of ways : by elimination of water 

 (formation of ester, glucoside or peptide linkages), by removal of hydrogen 

 (formation of disulphide bridges, methylene bridge, etc.), they are in- 

 fluenced by the oxido-reduction potential of the system. 



The theory of Frey-Wyssling postulates the existence of monomolecular 

 polypeptide filaments which must be about 20 A thick. However the 

 electron microscope has revealed the presence in the cytoplasm of an 

 endoplasmic reticulum made up of trabeculae 30 to 40 vayi in length, hollow 

 tubes joining together vesicles 100 to 300 nijx in diameter. Attached to this 

 system there are basophilic particles. In addition the cytoplasm contains 

 fibres either singly or in bundles, which make up the contractile material 

 of the cell and by means of a slow but continuous motion maintain the 

 various organelles suspended in the cellular fluid. 



Molecules such as the phosphatides can react with the protein side- 

 chains regardless of whether they are lipophilic or hydrophilic in nature, as 

 shovm in Fig. 84. 



Lecithia 



Polypeptide chain 

 Fig. 84 (Frey-Wyssling) — o = a water molecule. 



