Living Cells and What They Are Made Of 



19 



more. Fig. 2 shows the comparative sizes of some protein molecules 

 and some of the larger particles we shall meet later. 



It is evident that the task of determining how the constituent 

 amino acids are arranged in molecules of this magnitude is a very 

 difficult one. Up to the present it has only been completely achieved 

 in the one case of insulin, which has been studied by Dr F. Sanger, of 

 Cambridge. Analysis showed that the molecule of insulin contained 



Foot and 

 mouth virus 



Tobacco mosaic virus (half-length) 15,000,000 to 20,000,000 I 



Hemocyanin molecule (6,000,000) 



mZD Hemoglobin molecule (63,000) 

 l^" Albumin molecule (40,000) 



— Amino acid chain -10 units (1,300) 



• Sugar molecule (350) 



• Single amino acid molecule (130) 



0.1 ;x=100 m^jL = jo^oo 

 of a millimeter 



FIG. 2. Relative sizes of molecules of simple substances and proteins 

 and of virus particles and bacteria 



fifty-one amino acids of fifteen different kinds. These were arranged 

 in two distinct chains, one containing twenty-one amino acids and 

 the other with thirty amino acids. The exact order of the amino acids 

 in both of these chains have been determined by Dr Sanger and is 

 shown in Fig. 3. The two chains are joined together in two places by 

 cystine, which contains sulphur, through which the junction is made. 

 Insulin is a protein which is extracted from the pancreas of 

 animals. It is of great importance because it is involved in the utiliza- 

 tion of sugar in the body. The human disease, diabetes — an inability 



