MACROMOLECULES 107 



polypeptide chains joined by disulphide bridges) of the insuhn molecule. 

 Table X shows the amino acid sequence, as determined by Sanger, in a 

 series of polypeptides separated from fraction B of insulin. Sanger has 

 demonstrated that the only possible sequence corresponding to these many 

 peptides is that shown at the bottom of the table. 



III. NUCLEOPROTEINS 



The nucleoproteins are macromolecules formed by the union of proteins 

 and nucleic acids. The nucleic acids themselves are polymers of nucleo- 

 tides. The complete hydrolysis of the nucleic acids separated from nucleo- 

 proteins gives phosphoric acid, purines and pyrimidines (six members of 

 these two groups have been identified up to the present time), and two 

 furanose sugars. These latter are, either D-ribose (ribonucleic acids) or 

 2-desoxy-D-ribose (desoxyribonucleic acids). They have either two or 

 three -OH groups available for esterification. The number of possible 

 nucleotides entering into the composition of nucleic acids is, therefore, very 

 great. The purines, adenine and guanine, enter into the composition of all 

 nucleic acids. Among the pyrimidines, cytosine is present in all the nucleic 

 acids. Besides these purines and the pyrimidine which are always present, 

 one finds uracil in ribonucleic acids, and thymine and 5-methylcytosine 

 in desoxyribonucleic acids. Analysis of the nucleic acids reveals that they 

 are polymers of nucleotides. However, we are still far from knowing the 

 nature of the complex mixture of polynucleotides which make up each 

 nucleic acid. The little that is known at the present time is due to a com- 

 bination of the results of chemical hydrolysis and step-wise degradation by 

 means of enzymes. 



A. Properties of the Two Types of NucLEit Acid 



(a) Ribonucleic Acids (RNA) 



These complex mixtures contain only four bases : adenine, guanine, 



cytosine and uracil. The relative proportion of each of these bases does not 



differ appreciably from unity. Considering that this is not the case for the 



REFERENCES 



Edsall, J. T. (1958). Aspects actuels de la biochimie des acides amins et desprotemes. 

 Masson, Paris. 



Fox, S. & Foster, J. F. (1957). Protein Chemistry. Wiley, New York. 



Neuberger, a. (1958). Syjnposiiim on Protein Structure. Methuen, London. 



Neurath, H. & Bailey, K. (1953-1955) The Proteins. Chemistry, Biological 

 Activity, and Methods. (A collaborative work by many specialists in this field, 

 it is both the most comprehensive and the most modem text book available.) 

 4 vols. Academic Press, New York. 



Springall, H. D. (1954). The Structural Chemistry of Proteins. (More concise 

 than the above, it gives a clear and constructive account of the methods and 

 results of the chemical study of protein structure.) Butterworths, London. 



